Chemistry Lesson Note For SS2 (Second Term) 2024

Chemistry lesson note for SS2 Second Term is now available for free. The State and Federal Ministry of Education has recommended unified lesson notes for all secondary schools in Nigeria, in other words, all private secondary schools in Nigeria must operate with the same lesson notes based on the scheme of work for Chemistry.

Chemistry lesson note for SS2  Second Term has been provided in detail here on schoolgist.ng

For prospective school owners, teachers, and assistant teachers, Chemistry lesson note is defined as a guideline that defines the contents and structure of Chemistry as a subject offered at SS level. The lesson note for Chemistry for SS stage maps out in clear terms, how the topics and subtopics for a particular subject, group works and practical, discussions and assessment strategies, tests, and homework ought to be structured in order to fit in perfectly, the approved academic activities for the session.

To further emphasize the importance of this document, the curriculum for Chemistry spells out the complete guide on all academic subjects in theory and practical. It is used to ensure that the learning purposes, aims, and objectives of the subject meant for that class are successfully achieved.

Chemistry Lesson note for SS2 carries the same aims and objectives but might be portrayed differently based on how it is written or based on how you structure your lesson note. Check how to write lesson notes as this would help make yours unique.

The SS2 Chemistry lesson note provided here is in line with the current scheme of work hence, would go a long way in not just helping the teachers in carefully breaking down the subject, topics, and subtopics but also, devising more practical ways of achieving the aim and objective of the subject.

The sudden increase in the search for SS2 Chemistry lesson note for Second Term is expected because every term, tutors are in need of a robust lesson note that carries all topics in the curriculum as this would go a long way in preparing students for the West African Secondary Examination.

This post is quite a lengthy one as it provides in full detail, the Chemistry-approved lesson note for all topics and sub-topics in Chemistry as a subject offered in SS2.

Please note that Chemistry lesson note for SS2 provided here for Second Term is approved by the Ministry of Education based on the scheme of work.

I made it free for tutors, parents, guardians, and students who want to read ahead of what is being taught in class.

SS2 Chemistry Lesson Note (Second Term) 2024

                                 SECOND TERM E-LEARNING NOTES

SUBJECT: CHEMISTRY                          CLASS: SS 2

SCHEME OF WORK

WEEK      TOPICS

1. Revision of last term’s work
2. Hydrogen: Configuration, possible oxidation, Isotopes of hydrogen and unique Position of hydrogen in the periodic table, Laboratory and Industrial preparation of hydrogen, Physical and Chemical Properties, compounds of hydrogen, Uses and Test of Hydrogen.
3.         Oxygen:  Laboratory and industrial preparation of oxygen, general properties of   

             oxygen- Physical and chemical properties of oxygen, Oxides of oxygen, Uses and   

             Test of oxygen

4.        Halogens: 1. Electronic Configuration of Halogens, Physical Properties of Halogens  

            and Gradation down the Group, Chemical properties of halogens and Gradation  

           down the group, Uses of halogens and their compounds.

5.       Halogens: Preparation of chlorine (Laboratory and Industrial), Properties of chlorine  

           (Physical and chemical), Hydrogen chloride gas: Laboratory preparation, Properties

           and uses, Test for HCl gas and Fountain experiment.

6.       Nitrogen: General properties of Nitrogen–group VA elements, Laboratory and

       Industrial preparation of Nitrogen, Properties and Uses of Nitrogen, Compound of nitrogen – Ammonia- Laboratory and Industrial Preparation, Properties and Uses, Test for Ammonia, Fountain experiment

7.       Mid-Term Break and Holiday ASSIGNMENT
8.       Nitrogen: Compounds of Nitrogen: Trioxonitrate(V) acid – Laboratory Preparation,  

           Properties and Uses, Trioxonitrate(V) salts- Action of heat, Test for trioxonitrate(V)    

           ions.

9.     Sulphur: General Properties of Group VIA Element, Allotropes and uses of sulphur,

         Compounds of sulphur- Trioxosulphate(IV) acids and its salts, Tetraoxosulphate(VI)

         acid: Industrial preparation, Reactions and uses.

10. Revision.

11 Examination.

WEEK 1:  Revision of last term’s work.

WEEK 2

TOPIC: HYDROGEN

CONTENT:

1. Configuration, possible oxidation, Isotopes of hydrogen and unique Position of hydrogen of hydrogen in periodic table,
2. Laboratory and Industrial preparation of hydrogen
3. Physical and chemical properties,
4. Compounds of hydrogen, Uses and test of hydrogen.

PERIOD 1: CONFIGURATION, POSSIBLE OXIDATION AND ISOTOPES OF HYDROGEN AND UNIQUE POSITION OF HYDROGEN OF HYDROGEN IN PERIODIC TABLE.

Hydrogen is the first element in the periodic table with nucleus and electron. It is a gas; diatomic molecule in which two atoms of hydrogen are covalently bonded. The atomic number of hydrogen is one. The electronic configuration of hydrogen is 1s¹. It has oxidation number of +1 and -1

ISOTOPES OF HYDROGEN

Hydrogen exhibits Isotope with Hydrogen or protium [₁¹H], Deuterium or heavy hydrogen [²₁H or D] and tritium [³₁H or T] as the Isotopes. These Isotopes have relative atomic masses of 1, 2 and 3 respectively.

HYDROGEN ISOTOPES

The Isotopes have similar chemical properties but different physical properties although tritium is radioactive.

UNIQUE POSITION OF HYDROGEN IN THE PERIODIC TABLE

It can lose this single electron to form positive ions[H⁺] just like the elements in groups [Li, Na, K, Rb, Cs and Fr] and based on the argument it can be considered to be placed in group 1 along with group 1 elements. However, the H⁺ ion is not stable like ions formed by group 1 elements. Most of the properties of H⁺ are not similar to the properties of group I elements.

 Hydrogen can also gain one electron to form hydride ion (H^–) similar to halogens (group 7 elements) forming halides ion. Thus hydrogen is unique and anomalous in being similar to two different groups of elements. With electro positive alkali and alkali-earth metals, hydrogen forms compounds like LiH, NaH, and CaH₂ etc. Similar to halogens form LiCl, Na, CaCl₂ etc. On being electrolysed these hydrides yield hydrogen or halogen at the anode showing the similarities between the two. The ionisation energy of hydrogen and halogen are comparable. While those of alkali- metal are very low. It is similar to halogen in been a non-metal, a bad conductor of heat and electricity and diatomic. Hydrogen form covalent compound like those of halogens.

EVALUATION

1. To which group does hydrogen belong?
2. What is the position of hydrogen in the periodic table?
3. Mention the existing Isotopes of hydrogen
4. Discuss the uniqueness of hydrogen

PERIOD 2: LABORATORY AND INDUSTRIAL PREPARATION OF HYDROGEN.

Laboratory preparation of hydrogen:

Hydrogen is liberated when active metals react with dilute mineral acid, water or steam.e.g action of zinc on H₂SO₄

Zn_(s) + H₂SO_4(aq)         ZnSO_4 (aq) +H_2 (g)

The hydrogen gas is dried by passing it through Calcium  chloride. The apparatus is set up as shown below.

Dilute hydrochloric acid can also be used in place of H₂SO_4. Magnesium and iron can be used in the place of zinc.

Zn_(s) + 2HCl _(aq)      ZnCl_{2 (aq)} + H_{2 (g)}

Mg_(s) + H₂SO_4 (aq)               MgSO_4(aq) + H_2 (g)

Dilute trioxonitrates (v) acid is never used in the preparation of hydrogen because of its  strong oxidizing property and it produces water instead of hydrogen on reaction with metals. However, very dilute trioxonitates (v) acid give out hydrogen on reaction with Magnesium.

Hydrogen can also be prepared in the laboratory in the following ways,

1. By the action of Sodium hydroxide on zinc metal or aluminium.

Zn_(s) + 2NaOH_(aq)              Na₂ZnO_2(s) + H_2(g)

2Al_(s) + 2NaOH_(aq) + 2H₂O_(l)          2NaAlO_2(s) + 3H_2 (g)

2. Action of steam on heated metals e.g. Iron, Magnesium.

3Fe_(s) + 4H₂O_(g)       →   2NaOH_(aq) + H_2(g)

PREPARATION OF DRY HYDROGEN

The hydrogen gas produced in the first method of flask containing concentrated tetraoxosulphate (vi) acid or anhydrous calcium (ii) chloride as d drying agents.

SUB TOPIC 2: INDUSRIAL PREPARATION OF HYDROGEN

Hydrogen can be prepared industrially by different methods. These methods are as follows;

From water gas; in this case, water gas and excess stream are passed over a catalyst such as Iron (III) oxide, Fe₂O₃ at a temperature of 723k. The products are hydrogen and carbon (iv) oxide as shown in the equation below.

CO_(g) + H_2 (g) + H₂O    ⇌        CO_2 (g) +2H_2 (g)

It is a reversible reaction. CO₂ is dissolved in water under pressure of 30atm or absorbed by caustic soda, leaving hydrogen in good yield. This is Bosch process.

H₂O_(l) + CO_{2( g)}           H₂CO_3(aq)

METHOD 2

From natural gas. E.g methane – when natural gas is heated to a temperature of 1000 [thermal cracking] hydrogen is produced as shown in the equation below

CH_4(g)    2H_2(g) + C_(s)

Methane [CH₄] is one of the main constituents of natural gas.

METHOS 3 – FROM HYDROCARBONS

When hydrocarbon e.g methane or propane mixed with steam it is heated to a temperature of 800 in the presence of nickel catalysts, CO(g) and H₂(g) are produced.

CH_4(g) + H₂O_(g)    CO_(g) + 3H_2(g)

The mixture of carbon (ii) oxide and hydrogen gas is called synthestic gas. The mixture of [CO_(g) + H_2(g) is reacted with more steam

CO_(g) + H_2(g) + H₂O_(g)   ⇋       CO_2(g) + 2H_2(g)

The CO_2(g) is removed by absorption in water or any alkali such as Sodium hydroxide [NaOH] solution.

METHOD 4 – FROM COAL

Here, steam is passed over red-hot coal to obtain water gas[CO + H₂]:

C_(s) + H₂O_(g)            CO_(g) + H_2(g)

The water gas [CO + H₂] is reacted with more steam in the presence of nickel or platinum catalyst to produce CO_(g) + H_2(g) + H₂O_(g)   ⇋       CO_2(g) + 2H_2(g)

METHOD 5- FROM ELECTROLYSIS OF BRINE

Hydrogen is obtained as a by- production in the electrolysis of brine for the large scale production of Sodium hydroxide and Chlorine H₂ can also be produced by electrolysis of acidified water

EVALUATION

1. What do you observe when a piece of sodium is placed on the surface of water?
2. With equations only, describe at least two more methods of laboratory preparation of hydrogen.
3. What the precaution that one must take while preparing Hydrogen.
4. With equations only describe the preparation of hydrogen from hydrocarbons.

PERIOD  3; PHYSICAL AND CHEMICAL PROPERTIES  OF HYDROGEN

PHYSICAL PROPERTIES

1. It is a colourless, odourless and tasteless gas which burns in air with a high pitch sound.
2. It is combustible and when it burns in the absence of gas, it burns quietly with pale blue flame.
3. It is the highest  known gas.
4. It is 14.4 times less than air.
5. It exists ad diatomic molecule [H₂ ]
6. At high pressure, hydrogen can be liquefy at a critical temperature of -235
7. It is neutral to litmus and is insoluble in water
8. It does not support combustion.

CHEMICAL PROPERTIES

The chemical reactions of hydrogen arise from the fact that it can donate its single electron to form a positive ion [H⁺]; it can accept electron [to give a dublet structure] to form a negative hydride ion [H^–] and it can share electron with another atom to form a covalent molecule.

1. Hydrides of hydrogen: An important reaction of hydrogen is the formation of hydride with metals and non-metals.

• Metallic hydrides: Hydrogen is slightly electro negative and forms ionic hydrides e.g. NaH (Na⁺+ H^-) with alkali metals which are strongly electro positive. These hydrides contain the hydride ion H^–

2Li + H₂   →  2LiH (Lithium hydride)

Ca + H₂           CaH₂[ Calcium hydride]

The hydrides react with water with the liberation of hydrogen.

CaH_2(s)  + 2H₂O_(l)             Ca[OH]_2(aq) + 2H_2(g)

(ii)   Non-metallic hydrides: Hydrogen forms mainly covalent compounds with less electropositive metals [e.g. aluminium] and with non-metals. These are covalent hydrides. The reaction is spontaneous as shown in the reaction with fluorine and chlorine.

F_2(g) + H_2(g)                  2HF    ——————-(1)

Cl_2(g) + H_2(g)               2HCl _(g) —————–(2)

The reaction with chlorine is explosive in the presence of sunlight. Reactions with oxygen, sulphur and nitrogen require the use of catalyst.

Hydrogen reacts with molten sulphur to form hydrogen sulphide which smells like a rotten egg and it also reacts with nitrogen to form ammonia.

H_2(g) + S_(s)          H₂S_(g) ————(3)

3H_2(g) + N_2(g)                2NH_{3(g)———(}4)

1. Hydrogen is strong reducing agent when it is passed over the heated oxides as shown below.

PbO_(s) + H_2(g)                  Pb_(s) + H₂O_(g)

FeO_4(s) + 4H_2(g)      ⇌          3Fe_(s) + 4H₂O_(g)

The reaction of tri-iron tetraoxide and hydrogen is a reversible reaction, other reduction reaction are

1. CuO_(s)+ H_2(g)               Cu_(s) + H₂O_(g)
2. ZnO_(s)+ H_2(g)              Zn_(s) + H₂O_(g)

• Fe₂O₃+ 3H_2(g)               2Fe(s) + 3H₂O_(g)

2. Hydrogen burns in air with pop sound and with formation of water [steam] as shown in the equation below.

2H_2(g) + O_2(g)             2H₂O_(g)

The reaction is explosive and gives out a large amount heat.

EVALUATION:

1. List three physical properties of hydrogen with equations where necessary.
2. With equations only represent the reaction of hydrogen with (i) non-metals (ii) metals.

PERIOD 4 : USES OF HYDROGEN AND COMPOUNDS OF HYDROGEN

1. It is used in the synthesis of ammonia as shown in the equation below

N_2(g) + 3H_{2(g)    ⇌}          2NH_3(g)

The ammonia formed is used in the manufacture of fertilizers, drugs, plastics, wares, dyes among others.

2. It is used in the hardening of vegetable and animal oils for the manufacture of Margarine, candles, soap among others. The hydrogenation reaction occurs at high pressure and in presence of catalyst.
3. It is used to inflate airships and balloons, but hydrogen is very flammable. The use of hydrogen in balloons, but hydrogen in very flammable. The use of hydrogen in balloons is due to its low density.
4. In oxy-hydrogen flames, small quantities of hydrogen are required to produce high temperature that can melt metals.
5. It is used in the synthesis of methanol and HCl(aq)
6. Hydrogen + powder coal + oil at high pressure and temperature when a mixture of hydrocarbon is called synthetic petroleum from petrol (gasoline) and lubricants are obtained.
7. Gaseous hydrogen is a constituent of coal gas and water gas, and liquid hydrogen is used as rocket fuel.

COMPOUNDS OF HYDROGEN

When hydrogen combines with other elements it forms hydrides

1. The hydrides of alkali and alkaline earth metals are crystalline solids with high melting points that conduct electricity when molten. They react with water to liberate hydrogen gas.

CaH₂ +   2H₂O      Ca(OH)₂   +   2H₂

2. Boron and aluminium form complex covalent hydrides which are important reducing agents especially in organic chemistry. Some of them are lithium tetrahydridoaluminate (iii) and sodium tetrahydridoborate (iii)

   TEST FOR HYDROGEN

If a lighted splint is plunged into a gas jar of hydrogen, it gives a pop sound.

EVALUATION

3. Enumerate five uses of hydrogen.
4. How can you test the presence of hydrogen in the laboratory?

GENERAL EVALUATION

OBJECTIVE TEST:

1. If the valency of hydrogen is one and that of oxygen is two the formula is ___________. (a) HO₂(b) H₂O (c) 2OH (d) H₂O₃
2. One of the Isotopes of hydrogen is _____________. (a) Ozone (b) Deuterium (c) diamond (d) graphite
3. Hydrogen is prepared in the laboratory by the action of dilute H₂SO₄on the following metals except (a) Zn (b) Na (c)Al (d)Fe
4. The gas given out when sodium reacts with water is ……….. (a) oxygen (b) hydrogen (c) nitrogen (d) Chlorine
5. On a large scale hydrogen is produced from ___________ (a) producer gas (b) water gas (c) coke (d) coal tar

ESSAY QUESTIONS

1. Describe how you can prepare a sample of hydrogen in the laboratory
2. Discuss the reducing properties of this gas
3. How do you test for hydrogen in the lab?
4. Enumerate five uses of hydrogen
5. Describe commercial preparation of hydrogen.

WEEKEND ASSIGNMENT

Read revised 2^nd Edition Comprehensive Certificate Chemistry by G.N.C Ohia, et al pages 245-253

PRE READING ASSIGNMENT

Read about oxygen and its properties.

WEEKEND ACTIVITY

Explain how oxygen can be prepare in the laboratory and in the industry

REFERENCE TEXTS

1. Revised 2^ndedition comprehensive certificate chemistry G.N.C Ohia, et al
2. New school chemistry for senior secondary by Osei Yaw Ababio.

WEEK 3

TOPIC: OXYGEN

CONTENTS:

1. GENERAL PROPERTIES OF OXYGEN, ELECTRONIC CONFIGURATION AND BONDING CAPACITY OF OXYGEN
2. LABORATORY AND INDUSTRIAL PREPARATION OF OXYGEN
3. PHYSICAL AND CHEMICAL PROPERTIES OF OXYGEN.
4. COMPOUNDS OF OXYGEN AND USES OF OXYGEN

PERIOD 1: GENERAL PROPERTIES OF OXYGEN

Oxygen is the most abundant element on earth. It is prepared in the laboratory by catalytic decomposition of Potassium trioxochlorate(V) or hydrogen peroxide. Industrially, it is prepared by the liquefaction of air followed by fractional distillation of liquefied air.

Oxygen, being strongly electronegative, is chemically very reactive. It reacts with most metals to form basic oxides which are ionic, they also reacts with most non- metals to form acidic oxides which are covalent molecules and they reacts with hydrocarbons,  fuels[to form CO₂ and H₂O. It rekindles a glowing splint to indicate its presence in any place.

The oxides of oxygen can be classified into basic, acidic, amphoteric and neutral oxides. Peroxide is prepared by the action of a dilute acid on the peroxides of certain metals. It is a strong oxidizing agent. However, in the presence of more powerful oxidizing agents, ozone, O₃, is an unstable allotrope of oxygen. The ozone layer in the atmosphere acts as a protective shield by preventing too much ultra-violet radiation from falling on earth and harming living organism.

Electronic Structure and Bonding Capacity Of Oxygen

Oxygen is an element in group (VIA) of the periodic table. Its atomic number is 8, and has an electronic configuration of 1_S² 2_S² 2_P⁴ ————-Electronic structure

Thus, oxygen forms a complete octet by either accepting two electrons from a donor to form O^2-in an ionic substance, or by sharing two electrons with other atoms to form a covalent substance. At room temperature and pressure, oxygen exists as a discrete gaseous diatomic molecule, O₂ the two toms are joined together by double covalent bond, O=O.

EVALUTION

1. What is the name of the most abundant element on earth?
2. Enumerate the main classes of oxides of oxygen
3. Oxygen belongs to which group in periodic table.
4. What is the atomic number of oxygen?
5. Write electronic structure of oxygen.

PERIOD 2: LABORATORY AND INDUSTRIAL PREPARATION OF OXYGEN

LABORATORY PREPARATION

There are two general and common methods for the laboratory preparation of oxygen

1. Thermal decomposition of salts containing anions rich in oxygen, e.g. Potassium trioxochlorate(v) KClO_3(s).

The equation for the reaction is given as shown below.

2KClO_3(s)                                      KCl_(s) + 3O_2(g)

2. Decomposition of hydrogen peroxide: In this case, no heat is applied to the decomposing substance, H₂O_2,but immediately, the MnO₂ touches H₂O_2, effervescence occurs releasing the gas oxygen as seen in the equation below.

2H₂O_(l)               2H₂O_(l) + O_2(g)

Dry oxygen gas is obtained by passing it through a woulf [wash] bottle containing conc. H2SO4; the gas is then collected by downward delivery (or upward displacement of air), since pure oxygen is slightly denser than air.

INDUSTRIAL PREPARATION

Oxygen is produced, in large quantity from the following sources.

1. From liquefied air: Oxygen is obtained industrially from atmospheric air by liquefaction, followed by fractional distillation of the liquefied air.

• Atmospheric air is purified by the removal of Carbon(IV) oxide, water vapour and dust.
• The purified air is compressed at a pressure of about 200 atmospheres, heated and then cooled. It is then allowed to expand suddenly, for further cooling.
• By successive heating and cooling, the pure air becomes liquefied at about -200[73k]. This process is called LIQUEFACTION.
• The liquefied air is then fractionated by boiling. Nitrogen, being more volatile, boils first at – 196[77k], leaving oxygen, which is about 99.5% pure. This separation technique is called FRACTIONAL DISTILLATION.

Liquefied oxygen is usually stored in cylinders for medical and industrial use.

2. By electrolysis: Oxygen, like hydrogen is obtained during the electrolysis of dilute H₂SO_4.

EVALUATION

1. Statetwo main processes involved in the manufacture of oxygen from air.
2. Outline industrial production of oxygen from air.

PERIOD 3: PHYSICAL AND CHEMICAL PROPERTIES OF OXYGEN

PHYSICAL PROPERTIES

1. Pure oxygen is colourless, odourless and tasteless.
2. It is slightly denser than air.
3. It is slightly soluble in water.
4. It is a diatomic (O₂) gas that is neutral to litmus paper.
5. It boils (turn to gas) at -183⁰C and solidifies at -225⁰C

CHEMICAL PROPERTIES

• Reaction with metals: Metals such as Na, K, Ca, Mg, Al, Zn burn brightly in oxygen. Metals such as silver, Gold and platinum do not react with oxygen. Oxides of metals are generally basic. e.g.

4Na_(s)+  O_2(g)               2Na₂O_(g)

• Reaction with non-metals: Some burning non-metals when lowered into a jar of oxygen, burn to form acidic oxides or acid anhydrides which when dissolved in water form acidic solutions. E.g.

CO_2(g) + H₂O_(l)       H₂CO_3(aq)

• Test for oxygen:Oxygen is identified by its ability to rekindle a glowing splint. Nitrogen (I) oxide does this as well but is distinguished from oxygen by its pleasant sickly smell while oxygen is odourless. Oxygen also reacts with nitrogen(II)0xide to give brown fumes of nitrogen(IV)oxide which nitrogen(I)oxide does not do.

NO _(g) + O_2(g)                   NO_2(g)

 Reaction of oxygen:

Oxidation and combustion:

Many compounds are oxidized when heated in oxygen (combustion). E.g. all hydrocarbons burn in oxygen to form carbon (iv) oxide and water, sulphides burn in oxygen to give sulphur (iv) oxides.

1. With carbon

C_(s) + O_2(g)                   CO_2(g)

2. With sulphur

S_(s) + O_2(g)                 SO_2(g)

3. With phosphorus

4P_(s) + 5O_2(g)                     P₄O_10(s)

4. Formation  of water: Hydrogen burns violently in oxygen with a pale –blue flame, to produce water.

2H_2(g) + O_2(g)                    2H₂O_(l)

5. Formation of Ozone: When a silent electric discharge is passed through oxygen, gaseous ozone, O₃, (trioxygen) is formed. The reaction is reversible:

3O₂(g)           ⇌          2O_3(g)

Ozone is an allotrope of oxygen. Allotropes are two or more different forms of the same element, in the same physical state. The phenomenon is called allotropy. Other elements that exhibits allotropy are sulphur, carbon and phosphorous.

EVALUATION

1. Write two equations for each, showing reaction of oxygen with metal and with non- metal.
2. Enumerate three physical properties of oxygen
3. List five chemical properties of oxygen.
4. Mention the allotropes of oxygen.

PERIOD 4:  COMPOUNDS OF OXYGEN

Binary Compounds of Oxygen- Classification of Oxides

Based on their acid –base properties, there are four classes of oxides of elements in Periods 2 and 3: acidic, basic, amphoteric and neutral.

Acid oxides: These are of non-metals which dissolve in water to form acidic solution. And react with base to form salt and water. Examples of acid oxides are P₅O₁₀, NO₂, SO₂, SiO₂ etc. They are called acid anhydride. E.g.

CO₂ +NaOH           Na₂CO₃   +   H₂O

SO₃ + 2KOH    K₂SO₄    +   H₂O

NOTE: SiO₂ is insoluble in water

Basic oxides: They are metallic oxides that are basic in nature because they react with acids to form salt and water only.  Examples are K₂O, MgO, CaO, Li₂O etc. Soluble basic oxides are called alkali. E.g.

Na₂O_(g)  +   H₂O_(l)         2NaOH_(aq)

Na₂O_(s) + 2HCl_(aq)         2NaCl_(aq)   +  H₂O_(l)

Amphoteric oxides: These are oxides that behave both like acidic and basic oxides. They react with both acid and base E.g. ZnO, Al₂O₃, PbO etc

ZnO(s) + H₂SO_4(aq)           ZnSO₄    +   H₂O_(l)

ZnO  +  2NaOH +   H₂O Na₂Zn(OH)₄

Neutral oxides: They are neither acidic nor basic in character. E.g. water, CO, N₂O

Peroxide oxides: These are higher oxides where O-O bond is present. They give hydrogen peroxide when reacted with a dilute acid. E.g. Barium peroxide BaO₂, Calcium peroxide CaO₂, Sodium peroxide Na₂O_2, Hydrogen peroxide H₂O₂ (most common).

USES OF OXYGEN

1. It is used in oxy-hydrogen for welding and cutting of metals. A mixture of hydrogen and oxygen can burn to produce a temperature of 2,500

2. In oxy- ethyne [oxy-acetylene] flame for welding and cutting of steel. The reaction is highly exothermic.

3. In respiration by plants and animals.

4. As breathing aids in hospitals, high altitude flying and sea- dividing.

5. In steel production by Linz- Donawitz [L-D] process.

6. Liquefied oxygen is used in explosives, and as a rocket fuel

The Ozone Layer and Green House Effect

The ozone layer or ozone shield is a region of Earth‘s stratosphere that absorbs most of the Sun‘s ultraviolet (UV) radiation. It contains high concentrations of ozone (O₃) in relation to other parts of the atmosphere, although still small in relation to other gases in the stratosphere. The ozone layer contains less than 10 parts per million of ozone, while the average ozone concentration in Earth’s atmosphere as a whole is about 0.3 parts per million. The ozone layer is mainly found in the lower portion of the stratosphere, from approximately 20 to 30 kilometres (12 to 19 mi) above Earth, although its thickness varies seasonally and geographically. It has been ascertained through observation from satellites, that the ozone layer has been depleted more over the Antartic and there is now the creation of ‘ozone hole’. This depletion or reduction in the levels of ozone in the ozone layer has caused worldwide changes in climate and sea levels caused by an increases warming of the atmosphere due to release of gases, principally, carbon(IV) oxide, CO₂, in what is termed ‘Green house effect’. Green house gases e.g. CO₂, water vapour, chlorofluorocarbons are transaparent to short wave radiation, but absorb radiation at certain long wavelengths. Thus, the gases form a blanket, trapping out-going heat, much as the glass or plastic does in a green house, thereby leading to rising sea levels and general atmospheric warming, as well as melting of ice and changes in vegetation. This has led to the problems of desertification and flooding.

EVALUATION

1. State three uses of oxygen.
2. Define four types of oxide with one example each.

GENERAL EVALUATION

OBJECTIVE TEST:

1. In which group is oxygen in the periodic table? (a) IV (b) VI (c) VII (d) IV
2. Which of the following is an allotrope form of oxygen? (a) oxide (b) Ozone (c) diamond (d) graphite
3. Oxygen is prepared by heating. (a) Na₂CO₃(b) KClO₃(c) K₂SO₄ (d) H₂S
4. The existence of two or more forms of the same element in the same physical state is known as. (a) Isotopic (b) allotropy (c) oxides (d) homologous.
5. Amphoteric oxides are oxides which (a) react with neither acids nor alkalis (b) react with both acids and alkalis (c) react with acid only (d) react base only.

ESSAY QUESTIONS

1. What is allotropy? Name an allotrope of oxygen.
2. Name the four classes of oxygen and give example of each class.
3. Describe the commercial preparation of oxygen.
4. Describe simple test to distinguish between oxygen and nitrogen(I)oxide
5. Name the product formed when the following are burnt in oxygen:

• Carbon (ii) sulphur (iii) phosphorous (iv) magnesium.

PRE READING ASSIGNMENT

Read about halogens.

WEEKEND ACTIVITY:

Describe the manufacturing of chlorine by the electrolysis of brine. State clearly the products liberated at the various electrodes and why these products were preferred.

WEEK 4

TOPIC: HALOGENS

CONTENT:

1. ELECTRONIC CONFIGURATION OF HALOGENS, PHYSICAL PROPERTIES OF HALOGENS  AND GRADATION DOWN THE GROUP.
2. CHEMICAL PROPERTIES OF HALOGENS AND GRADATION DOWN THE GROUP
3. USES OF HALOGENS AND THEIR COMPOUNDS.

PERIOD 1 AND 2: ELECTRONIC CONFIGURATION OF HALOGENS

Halogens are found in group (viii) of the periodic table and consist of fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I) and Astatine (At),.

The name halogen is of Greek origin meaning salt formers because they readily form salts from metals. Halogens are very reactive non- metals with remarkable similarities in properties. This is because each halogen atom has seven only one electron to attain the octet. They are strong oxidizing agents with varying oxidation Numbers. The halogens are highly electro negative elements. The halogens share electrons to form covalent compounds or accept electrons to form ionic compounds. It is the electronic configuration of halogens that accounts for their electronegative nature, oxidising ability and the fact that they form mainly single covalent bonds.

ELECTRO CONFIGURATION AND SOME PROPERTIES OF THE HALOGENS AND GRADATION OF THE PROPERTIES

PHYSICAL PROPERTIES OF THE HALOGENS

EVALUATION

1. What is the atomic number of chlorine?
2. With the knowledge of atomic number, draw the electronic configuration of chlorine.
3. What is the colour of chlorine gas?

PERIOD 3: CHEMICAL PROPERTIES AND GRADATION DOWN THE GROUP

The chemical reactivity of the halogens decreases down the group from fluorine to iodine. The halogens are good oxidising agents and their oxidising power decreases from fluorine to iodine. The halogens try to attain the stable noble gas configuration either by sharing electrons or by accepting electrons. The following reactions illustrate the reactivity trend among the halogens.

1. Halogens can react with metals as shown in the equations below

2Na_(s) + F_2(g)       2NaF_(s)

2. Halogens react with non-metals as shown below

C_(s) + 2F_2(g)         CF_4(s)

Xe+ 2F    XeF_4(s)

P_4(s) + 6I_2(s)           4PI_3(s)

P_4(s) + 6Cl_2(g)             4PCl_2(s)

P_4(s) + 10Cl_2(g)             4PCl_5(s)

H_2(g) + F_2(g)             2HF_(g)

H_2(g) + Cl_2(g)             2HC_l(g)

Br_2(g) + H_2(g)             2HBr_(g)

I_2(g) + H_2(g)               2HI_(g)

The order of reacting is F₂> Cl₂>Br₂>I₂. The acid strength of the hydrogen halides follow the order:

HI>HBr>HCl>HF

The stability of Hydrogen halides decreases from chlorine to iodine: HCl>HBr>HI.

Chlorine is now an electron acceptor and so are other halogens and in so doing acts as oxidising agents.

2Na_(s) + Cl_2(g)          2Na⁺Cl^–_(s)

The order of decreasing power as oxidising agents is F₂> Cl₂>Br₂>I₂.

2. More reactive halogen displaces the less reactive from aqueous solution

Cl₂ + 2Br^–            2Cl- + Br₂

Cl₂ + 2I^–           2Cl^– + I₂

Br₂ + 2I^–              2Br^–   + I₂

Iodine is a weak oxidizing agent.

4. Reaction with water.

2F_2(g) + 2H₂O_(l)           4HF_(g) + O₂

3F_2(g) + 3H₂O            6HF_(g) + O_3(g)

Cl_2(g) + H₂O_(l)              HCl_(aq) + HClO_(aq)

5. Reaction with Alkalis

Cl_2(g) + 2NaOH_(aq)            NaOCl_(aq) + NaCl + H₂O

3Cl_2(aq) + 6NaOH_(aq)          NaClO_3(aq) + 5NaCl + 3H₂O_(l)

Bromine and iodine react in a similar manner to form the oxobromate(v) and iodated(v) ions.

3Br_2(aq) + 6KOH_(aq)             KBrO_3(aq)

3I_2(aq) + 6KOH_(aq)             KIO_3(aq) +5KI_(aq) + 3H₂O_(l)

EVALUATION

1. Give one for each equation of reaction to demonstrate the reaction of Cl₂, Br₂, I₂and F₂

PERIOD 4: USES OF HALOGENS AND THEIR COMPOUNDS

1. Fluorine is used in rocket propulsion and in making Uranium(iv) fluoride. It is also used in making fluorocarbon compounds which are used as refrigerant, aerosol propellant, anaesthetics and fire extinguisher and fluids. The flouoro- carbons contain only carbon and fluorine and are extremely inert and also are used as polytetrafluoroethene[PTFE] with the trade name Teflon in making valves, seals, gaskets, electrical insulators among others.
2. CHLORINE: is used as oxidant in the manufacture of bromine and as bleach and germicide in treatment of water. Chlorine is used in production of HCl (hydrogen chloride) in commercial quantity, in the production of fabrics and papers and also insecticides. (e.g DDT)(3) Iodine dissolved in alcohol or potassium iodide [KI] is used as antiseptic for cuts and scratches.
3. HYDROCHLORIC ACID which is one of the most laboratory acid, is used to remove rust from steel sheet before galvanizing.
4. SODIUM OXOCHLORATE (I) [NaCLO] is used as disinfectant and for bleaching in laundries.
5. SODIUM OXOCHLORATE (1) decomposes on warming to sodium oxochlorate(v), NaCLO3 which is used as weed killer.
6. Tetrachloromethan and trichloroethene are degreasing solvents.
7. Polychloroethene is used in making plastics
8. Dettol is used as disinfectant and antiseptics.
9. Dichlorodiphenyltrichloroethane (DDT) and benezehexachloride are used as pesticides
10. Bromine finds application in the manufacture of dyestuffs and in making silver bromide used in photographic materials.

EVALUATION

Enumerate five uses of halogens you know

GENERAL EVALUATION

OBJECTIVE TEST:

1. What is the atomic number of chlorine? A. 35 B. 53 C. 82 D. 17
2. 2, 8,18,7 is the electronic configuration of    A. F B. Cl C. Br D. I
3. Why is the preparation of halogens carried out in a fume cupboard? A. they are odourless B. they are poisonous C. They are colourless D. They are harmless.
4. In halogens the order of decreasing power as oxidising agents is
5. F₂>Cl₂>Br₂>I₂B .Cl₂>F₂>Br₂>I₂C. Br₂>F₂>I₂>Cl₂ D. Br₂>Cl₂>F₂>I₂
6. In halogens, melting points and boiling points increase with an increase in A. Molecular mass B. Valence C. oxidation number D. Atomic number

ESSAY QUESTIONS

1. Name two natural compounds of halogens.
2. State the similarities in chemical properties of halogens giving balanced reactions.
3. Write on the following giving balanced reaction examples. Halogen reaction with

(i) water (ii) iron (iii) alkali

4. (a) What is the atomic number of chlorine? (b) Why is the preparation of halogens carried out in a fumed cupboard?
5. What are the chemical properties of halogens?

WEEKEND ASSIGNMENT

1. Read 2^ndedition comprehensive certificate chemistry by by G.N.C Ohia, et al, pages 272-284

PRE READING ASSIGNMENT

Read about the uses of halogens and laboratory and chemical preparation of chlorine

WEEKEND ACTIVITY

1. Write the formulae of the following.

(i) Chloroform (ii) iodoform   (iii) Carbon tetrachloride   (iv) fluorine molecule

2. What are the uses of Carbon tetrachloride?

REFERENCES

1. 2^ndEdition Comprehensive Certificate Chemistry By By G.N.C Ohia, et al.
2. New school chemistry for senior secondary schools by Osai Yaw Ababio reversed by L.E.S Akpanisi Herbert Igwe.

WEEK 5

TOPIC: HALOGENS

CONTENT:

1. PREPARATION OF CHLORINE (LABORATORY AND INDUSTRIAL)
2. PROPERTIES OF CHLORINE (PHYSICAL AND CHEMICAL)
3. HYDROGEN CHLORIDE GAS: LABORATORY PREPARATION PROPERTIES AND USES,
4. TEST FOR HCL GAS AND FOUNTAIN EXPERIMENT.

PERIOD1: PREPARATION OF CHLORINE (LABORATORY AND INDUSTRIAL)

In the laboratory chlorine is prepared by the oxidation of concentrated hydrochloric acid with manganese (IV) oxide. The mixture is heated to obtain a greenish- yellow gas (chlorine).

MnO_2(s) + 4HCl _(aq)   MnCl_2(aq) + 2H₂O + Cl₂

Chlorine is prepared industrial by the electrolysis of brine and molten metallic chlorides

EVALUATION

Describe the laboratory preparation of chlorine

PERIOD 2: PHYSICAL PROPERTIES OF CHLORINE

1. It is a greenish-yellow gas with an unpleasant choking smell.
2. It is denser than air.
3. It is slightly soluble in water.
4. It is poisonous.

The chemical properties od chlorine have been discussed under the general properties of halogens. Let’s discuss the oxidizing properties of chlorine.

1. Chlorine oxidizes hydrogen sulphide to yellow sulphur.

Cl₂  +  H₂S     2HCl  +  S

2. Bleaching property of chlorine

Chlorine bleaches by oxidation. When chlorine dissolves in water, it forms hydrochloric acid and oxochlorate (i) acid (chlorine water).

Cl2  +  H2O       HCl  +  HOCl

In bleaching oxochlorate (i) acid gives out oxygen atom. The oxygen atom then bleach the material by oxidation. This bleaching action is permanent because the material cannot be re-oxidize by atmospheric oxygen.

EVALUATION:

1. State four physical properties of chlorine.
2. Describe the bleaching action of chlorine.

PERIOD 3: HYDROGEN CHLORIDE GAS-PREPARATION, PROPERTIES AND USES.

Hydrogen chloride is prepared in the laboratory by the action of concentrated tetraoxosuphate (vi) acid on sodium chloride. The gas is dried by passing it through concentrated tetraoxosulphate (vi) acid and collected by downward displacement of air.

NaCl_(s)  +  H₂SO_4(aq)   Na₂SO_4(aq)  +  HCl_(g).

Dissolution of hydrogen chloride in water gives hydrochloric acid.

PHYSICAL PROPERTIES OF HYDROGEN CHLORIDE

1. It is a colourless gas with sharp irritating smell.
2. It is denser than air.
3. It is very soluble in water.
4. It turns moist blue litmus paper red.
5. It is soluble in non-polar solvent like methylbenzene. It solution in methylbenzene cannot conduct electricity because it does not undergo ionization when dissolved in methylbenzene. But when dissolved in water, it undergoes ionization and so conduct electricity becase of the presence of free mobile ions.

CHEMICAL PROPERTIES OF HYDROGEN CHLORIDE

1. It reacts with active metals to liberate hydrogen gas e.g

Zn_(s)   +  2HCl_(g)    ZnCl_2(s)  +  H_2(g)

2. It reacts with ammonia to form a dense white fume of ammonium chloride.

HCl_(g)  +  NH_3(g)    NH₄Cl_(s)

3. Hydrochloric acid (obtained when hydrogen chloride dissolved in water) reacts with metallic trioxocarbonate (iv) or metallic hydrogentrioxocarbonate (iv) to liberate carbon (iv) oxide.

2HCl_(aq)  +  Na₂CO_3(s)    2NaCl_(aq) +  H₂O_(l)  +  CO_2(g)

4. Hydrochloric acid (obtained when hydrogen chloride dissolved in water) precipitates silver chloride from solution.

AgNO_3(aq)  +  HCl_(aq)    AgCl_(s)  +  HNO_3(aq)

USES OF HYDROGEN CHLORIDE GAS AND HYDROCHLORIC ACID

1. It is used for the synthesis of vinyl chloride which is used for the manufacture of plastics.
2. Hydrochloric acid is used for pickling of metals prior electroplating.
3. Hydrochloric acid is for the synthesis and analysis of many compounds.

EVALUATION:

1. State three physical properties of hydrogen chloride.
2. Mention three chemical properties of hydrochloric acid.
3. State four uses of hydrogen chloride.

PERIOD 4: TEST FOR HCL GAS AND FOUNTAIN EXPERIMENT. 

WEEK 6

TOPIC: NITROGEN

CONTENTS:

1. GENERAL PROPERTIES OF NITROGEN–GROUP VA ELEMENTS, LABORATORY AND INDUSTRIAL PREPARATION OF NITROGEN,
2. PROPERTIES AND USES OF NITROGEN
3. COMPOUND OF NITROGEN – AMMONIA- LABORATORY AND INDUSTRIAL PREPARATION
4. PROPERTIES AND USES, TEST FOR AMMONIA, FOUNTAIN EXPERIMENT

PERIOD  1: GENERAL PROPERTIES OF NITROGEN – GROUP V ELEMENTS

Nitrogen and other group VA elements are non-metals and show two common valences of 3 and 5. They are electron acceptors and both form several acidic oxides. They also form similar hydrides and chloride e.g. Nitrogen and phosphorus form N₂O₃ and P₄O₆, N₂O₅ and P₄O₁₀, NH₃, PH₃, NCl₃ and PCl₃

Properties of VA elements

W = white, gr = grey, p = 28 atmospheres, r = red, s = sublimes

  LABORATORY AND INDUSTRIAL PREPARATION OF NITROGEN

• Laboratory preparation of nitrogen from air

Atmospheric air is passed through aqueous NaOH, in order to absorb carbon (iv) oxide.

2NaOH_(aq) + CO_2(g)             Na₂CO_3(aq) + H₂O

It is then passed over red-hot copper metal in a combustion tube in order to remove oxygen.

Cu(s) + O_2(g)               2CuO_(s)

The residual gas collected over water is Nitrogen contaminated with small quantity of noble gases. Other methods of preparing nitrogen in the laboratory include:

Preparation from Ammonia gas.

CuO_(s) + NH_3(g)               3Cu_(s) + H₂O_(g) + N_2(g)

From ammoniumdioxonitrate (iii)

NaNO_2(aq) + NH₄Cl_(aq)            NH₄NO_2(aq) + NaCl_(aq)

• Industrial preparation of nitrogen

Nitrogen is produced commercially from fractional distillation of liquefied air.

PROCEDURE: Carbon (iv) oxide is removed from air. This air is liquefied by subjecting it to succession compression and cooling processes.

Nitrogen is collected first after distillation before oxygen because it has a lower boiling point than oxygen.

Nitrogen is stored in steel in steel cylinders and sold as liquid nitrogen or as the compressed gas.

EVALUATION

1. Describe how nitrogen can be obtained from ammonia.
2. Name the reagents necessary for the laboratory preparation of nitrogen from air.
3. How is nitrogen obtained commercially?

PERIOD 2 :  PROPERTIES  AND USES OF NITROGEN

PHYSICAL PROPERTIES

• Pure nitrogen is colourless, odourless and tasteless
• It is insoluble in water
• It is lighter than air.
• It has no effect on litmus paper

CHEMICAL PROPERTIES

1. Combustion: Nitrogen gas is generally unreactive at ordinary temperatures and pressures. It does not burn and does not support burning. It extinguishes a lighted splint.
2. Reaction with metals. Magnesium ribbon burns in air to produce a mixture of magnesium oxide and magnesium nitricide, a white solid.

2Mg_(s) + O_2(g)                   MgO_(s)

3Mg_(s) + N_2(g)                Mg₃N_2(s)

Magnesium nitride decomposes on  addition of water to liberate ammonia gas

Mg₃N_2(s) + 6H₂O_(l)               3Mg(OH)_2(aq) + 2NH_3(g)

3. (a) Reaction with non-metals: (a) under conditions of high temperatures and pressures, and in the presence of finely divided iron as catalyst, nitrogen combines with hydrogen, to produce ammonia. The reaction in reversible.

N_2(g) + 3H_2(g)                2NH_3(g)

(b) Nitrogen combines with oxygen at high temperature and pressure to produce Nitrogen (ii) oxide, an unstable colourless and odourless gas. The reaction is reversible.

N_2(g) + O_2(g)       ⇌          2NO_(g)

 USES OF NITROGEN

1. In the Haber process in production of ammonia.
2. Liquid nitrogen is used as a refrigerant.
3. Due to its inertness and because it does not support combustion it is used for the following purposes:

(a)  For prevention of fire

(b) As a diluents: to reduce combustion (nitrogen is responsible for the low heating value of producer gas, and the low combustion rate of atmospheric oxygen.

(c) Nitrogen provides inert atmosphere for food processing and packaging, and during some chemical reactions.

NITROGEN CYCLE

The continuous circulation of nitrogen between the free gaseous nitrogen in the atmosphere and the combined nitrogen in the proteins of the living tissues is known as the Nitrogen circle.

Nitrogen is an essential element in the formation of proteins in plants and animals. Unfortunately, it cannot be used directly in its free gaseous state, except in the form of trioxonitrate (v) salts (Nitrate). There are various processes through which atmospheric nitrogen is converted into trioxonitrate (v) salts in the soil, the process are called FIXATION OF FIXING OF NITROGEN.

1. When there is a thunder storm or lightning electric discharges are produced, during which atmospheric nitrogen and oxygen combine to form unstable and colourless nitrogen (ii) oxide

N_2(g) + O_2(g)          2NO_(g)

The nitrogen (II) oxide readily combines with more oxygen, to form brown fumes of nitrogen (iv) oxide.

2NO_(g) + O_2(g)          2NO_(g)

The nitrogen (iv) oxide dissolves in rain water in the presence of oxygen, to produce a very dilute solution of trioxonitrate (v)   acid, HNO₃, which falls as acid rain.

4NO_2(g) + 0_2(g)         2NO_2(g)

2. Plants absorb trioxnitrate (v) salts through the roots for the formation of flesh, and the excess is excreted as urea-in urine and faeces. When plants and animal die and decay, the bacteria in the soil decompose the proteins into organic compounds of nitrogen which are then converted into ammonia and ammonium salts, by PUTREFYING bacteria. A portion of the ammonium salts, in alkali medium, is oxidized into trioxonitrate(v) salt by NITRIFYING bacteria, while the remaining portion in acidic medium is oxidized to nitrogen, by DENTRIFYING bacteria. The nitrogen eventually goes back into the atmosphere. This is the process that usually compensate for the lost of atmospheric nitrogen.
3. Manure and nitrogeneous fertilizers are being added to the soil periodically, in order to replace nitrogen that has been used up by crops or plants. The nitrogen cycle operates in nature such that the percentage of nitrogen in the atmosphere remains constant.

 THE NITROGEN CYCLE

EVALUATION

1. Name one process, which converts atmospheric nitrogen to nitrate (v) in the soil.
2. Explain the formation of trioxonitrate (v) acid in the nitrogen cycle.

PERIOD 3: COMPOUNDS OF NITROGEN-AMMONIA LABORATORY AND INDUSTRIAL PREPARATION

 OXIDES OF NITROGEN

The common oxides of nitrogen are:-Dinitrogen(i) oxide, N₂O- Nitrogen (ii) oxide, NO. Nitrogen (iv) oxide, NO₂, others are dinitrogen(iii) oxide, N₂O_3, a pale blue liquid at room temperature and dinitrogen(iv) oxide, N₂O₄, a yellow liquid below the room temperature and dinitrogen(v) oxide N₂O₅ that exists as an unusual white solid at room temperature.

 AMMONIA

 INDUSTRIAL PRODUCTION OF AMMONIA

 The Haber process: Ammonia is manufactured from its constituent elements by a process devised by a German chemist, Fritz Haber (1914). The raw materials used are: nitrogen (obtained from water gas or natural gas).A mixture of dried nitrogen and hydrogen in the ratio 1:3  by volume is subjected to a high pressure of 200 – 250 atmosphere, at about 450 and in the presence of finely divided iron as the catalyst; the reaction is exothermic and reversible

N_2(g) + 3H_2(g)        2NH_3(g)

Under these conditions, about 20% ammonia is produced.

Successive heating and cooling under pressure liquefy the ammonia gas produced and the uncombined nitrogen and hydrogen are recycled. The flow chart for the production of ammonia is shown

LABORATORY PREPARATION OF AMMONIA:

Ammonia is prepared in the laboratory by heating a mixture of ammonium salt and non-volatile base. Calcium hydroxide is preferred to sodium hydroxide because calcium hydroxide is cheap and non-deliquescent. Heating a mixture of ammonium chloride and calcium hydroxide produces ammonia gas. The drying agent for ammonia is calcium oxide (quick lime). Concentrated tetraoxosulphate (vi) acid and calcium chloride are not used to dry ammonia because they react with ammonia to form salts

NH₄Cl  +  Ca(OH)₂     CaCl₂  +  H₂O  +  NH₃

 EVALUATION

1. State the type of chemical bond between nitrogen and hydrogen atoms in a molecule of ammonia.
2. In the industrial production of ammonia.

• What name is given to the process?
• State one source of each of the starting material.
• What are the operating temperature and pressure?

PERIOD 4: PROPERTIES AND USES, TEST FOR AMMONIA, FOUNTAIN EXPERIMENT

PHYSICAL PROPERTIES OF AMMONIA:

1. It is a colourless gas with choking smell.
2. It is very soluble in water.
3. In large quantities, ammonia is poisonous.
4. It is 1.7 times less dense than air
5. It turns moist red litmus paper red.

CHEMICAL PROPERTIES OF AMMONIA

1. Ammonia burns in oxygen producing steam and nitrogen

4NH₃ + 3O₂    2N₂ + 6H₂O

Ammonia reacts with platinium- rhodium catalyst to form nitrogen (ii) oxide.

4NH₃ + 5O₂      4NO + 6H₂O

2. Ammonia reduces copper (ii) oxide

2NH₃ + 3CuO    3Cu + 3H₂O + N₂

3. Ammonium precipitates many metallic ions from solution as insoluble hydroxides.

FeSO_4(aq) + 2NH_3(aq) + 2H₂O_(l)   Fe(OH)_2(s) +   (NH₄)₂SO_4(aq)

                                                            ^{green  ppt}

USES OF AMMONIA

1. Ammonia is used in refrigeration, since it can be liquefied easily.
2. In softening water used in laundry, to prevent wastage of soap.
3. As a domestic cleaner- to neutralize as in sweat.
4. In treating insect stings- to neutralize methanoic acid injected by the insects
5. In the production of plastics by polymerization
6. In the production of ammonium salts. Fertilizer and trioxonitrate(v) acid.
7. As a precipitating regent for the identification of cations in solutions.

TEST FOR AMMONIA GAS

Place any ammonia salt in a test tube, add any alkali and heat the mixture. A colourless gas with choking smell is given off. The gas turns moist red litmus paper to blue and produces dense white fumes with hydrogen chloride gas (from concentrated HCl reagent bottle. The gas is ammonia

EVALUATION:

1. State four physical properties of ammonia
2. With chemical equation, describe how ammonia is used to precipitate Pb²⁺and Zn²⁺

GENERAL EVALUATION

 OBJECTIVE TEST:

1. Which of the following contains the highest number of molecules  at s.t.p?(Avogadro’s constant)= 6.02 × 10²³mol^-1(a) 1.0g of H₂ (H₂=2)  (b) 4.0g of N₂(N₂ = 28) (c) 8.0g of O₂ (O₂=32)  (d) 16.0g of O₃ (O₃= 48)
2. The laboratory preparation of nitrogen from air requires the removal of   (a) carbon(iv)oxide (b) water vapour (c) oxygen and carbon (iv)oxide (d) carbon (iv) oxide, oxygen and water vapour
3. Nitrogen combines reversibly with hydrogen under (a) catalyst (b) high voltage electric spark (c) the presence of traces of NO₂(d) platinium
4. Nitrogen combines directly with metals except. (a) Cu (b) Mg (c) Ca (d) Al
5. Oxidation of Nitrogen in Mg₃N₂is (a) -3 (b) +3 (c) -2 (d) +2

ESSAY QUESTIONS

1. Outline the laboratory preparation of Nitrogen from atmospheric air.
2. (a) State two physical properties of Nitrogen (b) Name the process used in the commercial production of nitrogen.
3. Describe the laboratory preparation of nitrogen with the following (i) magnesium (ii) oxygen
4. (i) What is the percentage by volume of nitrogen in air? (ii) Calculate the amount, in mole of magnesium nitride that can be obtained from 3.0g of magnesium (Mg =24)
5. (a) State how nitrogen resemble or differ from NH₃. (b) How does nitrogen resemble or differ from CO₂in its reaction with each of the following (i) litmus (ii) A burning candle (iii) burning magnesium

WEEK 8 TOPIC

1. NITROGEN: COMPOUNDS OF NITROGEN: TRIOXONITRATE(V) ACID –   

LABORATORY   PREPARATION AND PHYSICAL PROPERTIES

2. CHEMICAL PROPERTIES OF  TRIOXONITRATE (V) ACID  
3.  USES OF TRIOXONITRATE (V) ACID
4. TRIOXONITRATE(V) SALTS- ACTION OF HEAT, TEST FOR TRIOXONITRATE(V)   

IONS.

PERIOD 1: NITROGEN: COMPOUNDS OF NITROGEN: TRIOXONITRATE(V) ACID –   

LABORATORY PREPARATION AND PHYSICAL PROPERTIES       

LABORATORY PREPARATION OF TRIOXONITRATE (V) ACID

Trioxonitrate (v) acid is prepared by heating solid sodium trioxonitrate (v) with concentrated tetraoxosulphate (vi) acid.

NaNO₃ + H₂SO₄  HNO₃ + NaHSO₄

The apparatus used is completely made of glass because rubber and cork are attack by trioxonitrate (v) acid. The trioxonitrate (v) acid produced in this case is yellow in colour due to the slight decomposition of the acid by heat to produce reddish-brown gas (nitrogen (iv))   which then dissolve in the acid to impart the yellow colour.

4HNO₃  H₂O + 4NO₂ + O₂

PHYSICAL PROPERTIES OF TRIOXONITRATE (V) ACID

1. It is corrosive and readily destroys organic materials.
2. It turns blue litmus paper red.
3. It is a colourless liquid which fumes in air on exposure.

EVALUATION:

1. Explain why trioxonitrate (v) acid produced in the laboratory is yellow in colour.
2. Why is all-glass apparatus used in the preparation of trioxonitrate (v0 acid.
3. State three physical properties of trioxonitrate (v0 acid.

PERIOD 2: CHEMICAL PPROPERTIES OF TRIOXONITRATE (V) ACID

1. Reaction as an acid:

(a) It reacts with base to form salt and water

HNO₃ + NaOH   NaNO₃ + H₂O

(b) It reacts with trioxonitrate (v) to liberate carbon (iv) oxide

HNO₃ + CaCO₃   Ca(NO₃)₂ + H₂O + CO₂

2. As an oxidizing agent:

(a) with metals: Trioxonitraye (v0 acid is a strong oxidizing agent and the oxidizing power of trioxonitrate (v) acid depends on its concentration. In concentrated form, it oxidizes certain metal to trioxonitrate (v) while the acid is reduced to nitrogen (iv) oxide and in moderately concentrated form it reduced to nitrogen (ii) oxide.

Cu + 4HNO₃  Cu(NO₃)₂ + 2H₂O + 2NO₂

3Cu  +  8HNO₃  3Cu(NO₃)₂ + 4H₂O + 2NO

Lead, mercury and silver react in similar way to copper with the metal

Magnesium, zinc nad iron react with dilute trioxonitrate (v) acid to give ammonium trioxonitrate (v0 or nitrogen (i) e.g

4Zn + 10HNO₃  4Zn(NO₃)₂ + 3H₂O + NH₄NO₃

Aluminium and iron do not react with concentrated HNO₃ due to initial formation of an oxide coating on the metal, which prevent further reaction.

(b) With non-metals: Hot concentrated tetraoxosulphate (vi) acid oxidizes non-metals to their oxides, which may dissolve in water to for the corresponding acids.

C + 4HNO₃  CO₂ + 2H₂O + 4NO₂

S + 6HNO₃   H₂SO₄ + 2H₂O + 6NO₂

P + 5HNO3    H₃PO₄ + H₂O + 5NO₂

I₂ + 10HNO₃     2HIO₃ + 4H₂O + 10NO₂

EVALUATION:

1. Explain why metals can displace hydrogen from trioxonitrate (v0 acid.
2. State three chemical properties of trioxonitrate (v0 acid

PERIOD 3: USES OF TRIOXONITRATE (V) ACID

1. It is an important raw material for the manufacture of many useful trioxonitrate (v0 salts and organic nitro-compounds such as those used for making dyes. Explosives, fertilizers and drugs.
2. It is used for making of nylon and terylene.
3. It is useful oxidizing agent for many purposes in the laboratory.

EVALUATION:

State  four uses of trioxonitrate (v0 acid.

PERIOD 4: TRIOXONITRATE(V) SALTS- ACTION OF HEAT, TEST FOR TRIOXONITRATE(V)   

IONS.

All trioxonitrate (v) salts are decomposed by heat.

(a) Trioxonitrate (v0 of sodium and potassium are decomposed to the dioxonitrate (iii) compound and oxygen.

NaNO₃  NaNO₂ + O₂

(b) Trioxonitrate (v) of Zn, Cu, Fe, Mg, Ca, Pb and Al are decomposed to the oxide of the metal, nitrogen (iv) oxide and oxygen.

2Pb(NO₃)₂   2PbO + 4NO₂ + O₂

(c) Trioxonitrate (v) of Hg and Ag are decomposed to the metal, oxygen and nitrogen (iv0 oxide because the metal oxides are unstable to heat

2AgNO₃     2Ag + 2NO₂ + O₂

TEST FOR TRIOXONITRATE (V0 IONS

BROWN RING TEST

Acidify an unkwon solution with dilute tetraoxosulphate (vi) acid, then add some freshly prepared iron (ii) tetraoxosulphate (vi) and shake. Then keep the test tube in a slanting position and carefully add some concentrated tetraoxosulphate (vi) acid down the side of the test tube. A brown ring will be formed ar the junction of the two liquid layers. This shows that the unknown contains trioxonitrate (v) ions. the brown ring is FeSO₄.NO

GENERAL EVALUATION:

OBJECTIVE TEST

1. Nitrogen combines directly with metals except (a) Ca (b) Mg (c) Cu (d) Al
2. Oxidation number of nitrogen in Mg₃N₂is (a) -3 (b) +3 (c) -2 (d) +2
3. Hydride of nitrogen which is capable of turningred litmus blue make nitrogen to have an oxidation state of (a) +2 (b) -2 (c) +3 (d) -3
4. Pyre trioxonitrate (v0 acid is colourless but the product of its laboratory preparation is yellow because of the presence of dissolved (a) sulphur (b) sulphur (iv) oxide (c) nitrogen (iv) oxide (d) nitrogen (ii) oxide
5. Which of the following will not leave a solid residue when decomposed by heat? (a) (NH₄)₂SO₄(b) NaNO₃(c) Ca(NO₃)₂ (d) KNO₃

ESSAY

1. Explain what is observed when lead (ii) trioxonitrate (v) is heated.
2. Explain why iron (ii) tetraoxosulphate (vi) is always prepared freshly whenever is to be used for analysis.
3. Explain why trioxonitrate (v) acid is not used to acidify KMnO₄solution.

PRE READING ASSIGNMENT

Read about allotropes of sulphur on page 381 of New School chemistry by Osei Yaw Ababio

WEEK ACTIVITY

Draw the nitrogen cycle in New School chemistry by Osei Yaw Ababio

WEEK 9

TOPIC: SULPHUR

CONTENTS:

1. GENERAL PROPERTIES OF GROUP VIA ELEMENT
2.  ALLOTROPES AND USES OF SULPHUR
3. COMPOUNDS OF SULPHUR- TRIOXOSULPHATE (IV) ACIDS AND ITS SALTS
4. TETRAOXOSULPHATE (VI) ACID: INDUSTRIAL PREPARATION, REACTIONS AND USES.

PERIOD 1: GENERAL PROPERTIES OF GROUP VIA ELEMENT

Group VIA elements usually called oxygen family have the following properties

• They are made up of oxygen (O), sulphur (S), Selenium (Se) Tellurium (Te) and Polonium (Po)
• Oxygen gas is the first member of the group
• Sulphur comes as the second member of the group and it is a solid, followed by other members.
• They have six valence electrons.
• They gain two electrons usually from group I and II metals to attain octet structure or form negative divalent ions e.g. S₂, O₂
• They form covalent compounds with non-metals e.g. H  —–O——–H in water and H—-S—–H , hydrogen sulphide
• Their oxidation states range from -2 in its compounds except peroxides like H₂O₂and K₂O₂ where oxygent has -1

 ELECTRON STRUCTURE OF SULPHUR

Sulphur is represented with a symbol S, it has 16 atomic numbers. The electronic configuration is 2, 8,6. It is a P block element. Thus have its valence electrons in the p orbital Is² 2s² 2p⁶ 3s²3p⁴

The distribution of electrons into shell is given in the figure below:

Electronic configuration of sulphur

EVALUATION

1. Enumerate any five (5) general properties of group VIA elements.
2. Explain briefly the electron structure of sulphur

PERIOD 2: ALLOTROPES AND USES OF SULPHUR

Sulphur exhibits the phenomenon of allotropy. Allotropy is the existence of an element in two or more different forms in the same physical state. The various forms are known as allotropes. The allotropes of sulphur are Rhombic (or  – sulphur), Monoclinic or prismatic – sulphur), Amorphous sulphur (S- sulphur), Plastic sulphur

Rhombic and monoclinic sulphur are crystalline in nature and are actually the important allotropes.

• Rhombic sulphur (α- sulphur): free sulphur exists as allotrope at below 96. It has octahedral structure made up of S₈ The colour is brightly yellow and has a melting point of 113and density of 2.08gcm^-3

PREPARATION

Rhombic sulphur is prepared by allowing a saturated solution of sulphur in carbon (IV) sulphide (carbon disulphide) in a test tube kept   below C to evaporate slowly. Octahedral crystals will gradually deposit. This preparation should be done in a fume cupboard because of the poisonous and flammability of carbon disulphide

• Monoclinic sulphur (β– sulphur): It is the only stable allotrope between 96and 119 and consists of long, thin and needle shaped. The colour is amber. At room temperature it changes to rhombic sulphur crystals. Monoclinic sulphur has a melting point of 119^oC and density of 1.98gcm^-3

PREPARATION

Monoclinic sulphur is obtained by cooling molten sulphur. Powdered sulphur is heated in a crucible till it melts into amber -coloured liquid. More sulphur is added, heated and stirred at the same time. This process is repeated until the crucible is filled with molten sulphur. It is then allowed to cool while a hard crust formed at the top. Piercing one or two holes through the crust and pouring off the remaining molten sulphur reveals a needle shaped crystals of monoclinic sulphur deposited on the sides of the crucible.

Rhombic sulphur                   monoclinic sulphur

1. Amorphous sulphur: it is pale – yellow in colour and has no regular crystalline shape. It is prepared as a deposit when hydrogen sulphide is bubbled through water for a long time and the saturation exposed to air. It can also be prepared by the action of dilute HCl acid on trioxothiosulphate (v) solution

H₂S _(g) + O_2(g)         →    2H₂O_(g) + S_(g)

S₂O₃^2-_(aq) +2H⁺_{(aq)    →}     2H₂O_(l) + SO_2(g) + S_(s)

1. Plastic sulphur: this is prepared by heating yellow sulphur until it boils in a test tube. The boiling sulphur is poured into cold water is seen to roll up into yellow ribbons which look like a plastic. It changes to rhombic sulphur after sometime. It is therefore said to be unstable.

EVALUATION

1. (a) What is allotropy? (b)(i) Name two allotropes of sulphur (ii) State two differences between them.
2. Explain briefly, how Rhombic and monoclinic sulphur are obtained.
3. Describe the formation of plastic sulphur and amorphous sulphur.

PROPERTIES OF SULPHUR

PHYSICSL PROPERTIES

1. Sulphur is a yellow solid existing in crystalline or amorphous
2. It is non-metallic and exhibits allotropy.
3. It sublimes to give flowers of sulphur.
4. It is a non-conductor of heat and electricity.
5. When heated in the absence of air, roll sulphur undergoes the following changes:

• at 115⁰C it forms amber – coloured liquid.
• at about 115⁰C the liquid becomes dark and discourse.
• near its boiling point, becomes mobile again and reddish brown in colour.
• at its boiling point of 44⁰C it gives off a brown vapour, condensing this vapour on a cold surface gives flowers sulphur.

CHEMICAL PROPERTIES

(i) Combustion in air: sulphur burns in air with a blue flame to produce sulphur (iv) oxide.

S_(s) + O_2(g) →   SO_2(g)

(ii) Reaction with metals: sulphur combines directly with metals to give the corresponding anhydrous sulphides

Fe_(s) + S_{(s )  →} FeS_(s)

2Cu_(s) + S_{(s)   →}   Cu₂S_(s)

(iii) Reaction with non- metals:  sulphur reacts with coke in the furnace to produce carbon (IV) sulphide

C_(s) +2S_{(s)    →}   CS_2(l)

(iv).  As a reducing agent: when powdered sulphur is warmed with concentrated H₂SO₄, it is oxidized to SO₂, while its acid is reduced to SO₂.

S_(s)   +   H₂SO_4(aq)   → 2H₂O_(l) + 3SO_2(g)

 USES OF SULPHUR

1.  Used in the production of tetraxosulphate (VI) acid.
2.  Used in vulcanizing rubber. It makes raw rubber to become hard, tough and elastic and hence, suitable for making tyres
3.  Used in the production of carbon (iv) sulphide used as a solvent and insecticides
4. It is used in gun powder and matches, dyes tuffs fungicides, ointment and germicides
5. Also used in the production of calcium hydrogen trioxosulphate (iv), Ca(HSO₃)₂used in bleaching wood pulp for making news prints

EVALUATIONs

1. (a) What is flower of sulphur (b) what are the products of reaction of sulphur with it concentrated H₂SO₄acid
2. Mention three(3) physical and four (4) chemical properties of sulphur
3. Itemize the uses of sulphur

PERIOD 3: COMPOUNDS OF SULPHUR- TRIOXOSULPHATE (IV) ACIDS AND ITS SALTS

Trioxosulphate (IV) acid is a dibasic acid which is obtained by dissolving sulphur (IV) oxide in water.

LABORATRY PREPARATION OF TRIOXOSULPHATE (IV) ACID

It is prepared by the action of dilute hydrochloric acid on heated sodium trioxosulphate (iv) to produce sulphur (iv) oxide which is then dissolved in water.

Equations of the reactions

(a) Na₂SO_3(s)    + 2HCl_(aq)  → 2NaCl_(qg)  + SO_2 (g) + H₂O_(l)

(a) SO_2 (g) + H₂O _(l) → H₂SO_{3 (aq)}

Sulphur (IV) oxide is the acidic hydride of trioxosulphate (IV) acid.

PHYSICAL PROPERTIES OF TRIOXOSULPHATE (IV) ACID

1. It isa colourless liquid, which smells strongly of SO₂.
2. 2. It turns blue litmus paper red.
3. It mixed readily with water.
4. It has an irritating and choking smell.

CHEMICAL PROPERTIES OF TRIOXOSULPHATE (IV) ACID

1. Trioxosulphate (iv) acid is a weak dibasic acid. In the presence of a limited amount of sodium hydroxide an acid salt, sodium hydrogen trioxosulphate (IV) is formed.

2NaOH _(aq) + H₂SO_{3 (aq)} → Na₂SO_{3 (aq )} + 2H₂O_(l)

However, when the alkali, sodium hydroxide, is in excess, the normal salt sodium trioxosulphate (IV) is produced. That is, complete neutralisation takes place.

NaOH _{(aq )}+ H2SO3_(aq)→ NaHSO3_(aq), + H2O_(l)

2. It is oxidized in air t tetraoxosulphate (VI)acid.                                                                                                                H₂SO_4(aq)+ O_2(g) →2H₂SO_4(aq)
3. Reducing properties

It is a strong reducing agent. It decolourises the purple colour potassium tetraoxomanganate (vii) solution, and changes the colour of potassium heptaoxodichromate (VI) from orange to green.

4. Bleaching properties:dyes are bleached by aqueous solution of trioxosulphate (IV) acid. It bleaches by reduction. Material bleached by trioxosulphate(iv) acid and sulphur (iv) oxide temporal, it can be re-oxidized by atmospheric oxygen.

USES OF TRIOXOSULPHATE (IV) ACID

1. It is used for bleaching.
2.  It is also used as a germicide.

TRIOXOSULPHATE (IV) SALTS

Trioxosulphates (IV) are the salts of trioxosulphate (IV) acid.

LABORATORY PREPARATION OF TRIOXOSULPHATE (IV) SALTS

1. By the action of trioxosulphate (iv) on excess alkali. Sodium hydroxide is used.

H₂SO_{3 (aq)} + NaOH _(aq) →  Na₂SO_3(aq) + 2H₂O_(l)

This is a neutralization reaction.

2. Precipitation of an insoluble trioxosulphate (IV) from the solution of its metallic salt by sulphur (iv) oxide.

SO_{2 (g)} +2H₂O _(l) +ZNNO_{3 (ag)} → ZnSO_3(s) +HNO_{3 (l)}

PHYSICAL PROPERTIES OF TRIOXOSULPHATE (IV) SALTS

Most of the trioxosulphates (IV) are insoluble in water but the trioxosulphate (IV) of calcium; ammonium, potassium and sodium are soluble in water.

CHEMICAL PROPERTIES OF TRIOXOSULPHATE (IV) SALTS

1. They liberate sulphur (IV) oxide on reaction with aqueous hydrochloric acid e.g. Na₂CO₃,

Na₂CO_{3 (aq)} + 2HCl _(aq)   → 2NaCl _(aq) + H₂O _(l) +SO_{2 (g)}  

2. When exposed to air trioxosulphate (IV) salts are slowly oxidised to tetraoxosulphate (VI) salts.
3. On addition of barium chloride solution into solution of trioxosulphate (IV) white precipitate of barium trioxosulphate (IV) which is soluble in dilute hydrogen chloride (HCl) is formed.

BaCl_2 (aq) + Na₂SO_{3 (aq)} → BaSO_3(s) + 2NaCl _(aq)

TEST FOR TRIOXOSULPHATE (IV) SALT

1. On warming with dilute hydrochloric acid sulphur (IV) oxide is given off.
2. Add solution of barium chloride to the solution of the substance suspected to be trioxosulphate (IV). Any white precipitate (barium trioxosulphate (IV)), soluble in dilute hydrochloric acid confirms the presence of a trioxosulphate (IV) ion e.g. Na₂SO_3.

BaCl_2 (aq) + Na₂SO_{3 (aq)} → 2NaCl _(aq) + BaSO_3(s)

DIFFERENTIATING TRIOXOSULPHATE (IV) AND TETRAOXOSULPHATE (VI) IONS

For trioxosulphate (IV), the white precipitate (barium trioxosulphate (IV)) is soluble in dilute hydrochloric acid, while the precipitate from tetraoxosulphates (VI) is insoluble in dilute hydrochloric acid.

PERIOD 4: TETRAOXOSULPHATE (VI) ACID: – INDUSTRIAL PREPARATION, REACTIONS AND USES.

Tetraoxosulphate (VI) Acid is a chemical compound with the formula H₂SO₄.

INDUSTRIAL PREPARATION OF TETRAOXOSULPHATE (VI) ACID – H₂SO₄

The industrial or commercial production of H₂SO₄ is through a process known as the contact process. The process involves:

1. The oxidation of sulphur (IV) oxide by air to sulphur (VI) oxide using a catalyst such as vanadium (V) oxide, V₂O₅.

SO₂ is produced by burning sulphur or by burning pyrite, FeS₂ in air.

S + O₂     SO₂

2SO_2(g) + O₂      2SO_3(g)

2. The absorption of sulphur (VI) oxide, SO₃ in conc. H₂SO₄to form a fuming liquid called ‘Oleum’- heptaoxosulphate (VI) acid.

H₂SO_4(aq)+ SO_3(g)→ H₂S₂O_7(aq)– oleum

3. The oleum is diluted with correct amount of water to produce the conc. H₂SO₄.

H₂S₂O_7(aq)+ H₂O_(l)→ 2H₂SO_4(aq)

Note: a direct absorption of SO₃ in water is not done – the reaction is violently exothermic, the heat evolved will cause the acid to boil producing a mist of fine drops of di H₂SO₄ which will fill the environment.

PROPERTIES OF H₂SO₄

1. As an acid – H₂SO₄is dibasic and ionizes almost completely in solution, this makes it a strong acid. Due to it being dibasic, it forms two kinds of salts with alkalis.

2NaOH_(aq)+ H₂SO_4(aq)→ Na₂SO_4(aq)+ 2H₂O_(l) and

NaOH_(aq)+ H₂SO_4(aq)→ NaHSO_4(aq)+ H₂O_(l)

2. Action of dilute H₂SO₄on metals Reactive metals would displace hydrogen from dilute tetraoxosulphate(VI) acid.

Zn_(s)+ H₂SO_4(aq)→ ZnSO_4(aq)+ H_2(g)

Note:* Less reactive metals such as copper will not displace hydrogen from dilute acid.* Cold concentrated H₂SO₄ is not attacked by any metal in the complete absence of water.

3. Action on trioxocarbonate(IV) ,Carbon(IV) oxide is liberated when H₂SO₄is added onto a trioxocarbonate(IV).

Na₂CO_3(aq)+ H₂SO_4(aq)→ Na₂SO_4(aq)+ H₂O_(l)+ CO_2(g) On a piece of marble, which has the chemical formula CaCO₃, the reaction obtained is prematurely stopped due to the formation of the sparingly soluble salt, CaSO₄, which forms a deposit on the surface of the marble.

4. Conc. H₂SO₄as an oxidizing agent When hot and concentrated, the acid accepts electrons from reducing agents such as Cu or Zn. It also oxidizes non-metals, such as carbon and sulphur, and is reduced to SO₂in the process.

S_(s)+ 2H₂SO_4(aq)→ 2H₂O_(l)+ 3SO_2(g)

C_(s)+ 2H₂SO_4(aq)→ 2H₂O_(l)+ 2SO_2(g)+ CO_2(g)

The SO₂ given off is detected using a strip of filter paper moistened with potassium heptaoxodichromate (VI) solution which turns orange to green – this is one of the tests for SO₂ discussed earlier.

5. As a dehydrating agent Tetraoxosulphate (VI) acid has a strong affinity for water. The addition of the acid to water (conc. acid should always be gradually added to water, with stirring of the liquid as the acid is added – to prevent the acid from forming a lower layer) produces a great amount of heat, hence the addition is not a physical change, but a chemical change.H₂SO₄is hygroscopic, that is, it absorbs water from the air and becomes dilute. When conc. H₂SO₄is added to many compounds, it decomposes them by removing elements water  from them, that is, it dehydrates them. An example is the removal of rust from iron, and the dehydration of sugar. The sugar becomes a black mass of carbon. Dehydration is the removal of elements of water from a substance and the chemical composition of the substance is changed.

C₁₂H₂₂O_11(s)  +  nH₂SO_4(l)→ 12C_(s)+  11H₂O_(l)+ nH₂SO_4(aq))

In a similar way, conc. H₂SO₄ acts on the skin and cloth.

TEST FOR TETRAOXOSULPHATE (VI) ION

The characteristic test for any soluble tetraoxosulphate(VI) is the formation of white precipitate (barium sulphate) when a solution of barium chloride, acidified with dilute HCl, or when a solution of barium trioxonitrate (v), acidified with dilute trioxonitrate (v) acid is reacted with it.

BaCl_2(aq)+ Na₂SO_4(aq)→ 2NaCl_(aq)+ BaSO_4(s)

Ba(NO₃)_2(aq)+ Na₂SO_4(aq)→ 2NaNO_3(aq)+ BaSO_4(s)– white precipitate

Ionically, it represented thus

USES OF TETRAOXOSULPHATE (VI) ACID

Below are some of the uses of H₂SO₄

1. for the manufacture of fertilizer, such as ammonium tetraoxosulphate (VI), (NH₄)₂SO₄, and superphosphates.
2. for the manufacture of paints and pigments.
3. for the manufacture of artificial and natural fibre.
4. for the manufacture of metallic tetraoxosulphate (VI), HCl, HNO₃, HF, and plastics.
5. for the manufacture of detergents, dyes, explosives and drugs.
6. for the extraction of metals, example, in pickling (cleaning) iron and steel before plating them with tin or zinc.
7. as electrolyte in lead-acid storage battery.
8. In petroleum refining, where to is used to wash impurities out of gasoline and other refinery products

GENERAL EVALUATION

OBJECTIVE TEST:

1. If sulphur is dissolved in carbon(iv) sulphide and the solution is allowed to evaporate, the allotrope of sulphur formed is (a) plastic sulphur (b) amorphous sulphur (c) Rhombic sulphur (d) monoclinic sulphur (e) colloidal sulphur
2. Sulphur is used for the following except. (a) Coating of steel to prevent rusting (b) vulcanization of rubber (c) prevention of growth of fungi (d) manufacture of dyes (e) manufacture of H₂SO₄acid
3. Mono clinic and Rhombic are allotropes of (a) carbon (b) oxygen (c)  Neon (d) Polonium (e) sulphur
4. The crystalline allotrope of sulphur that is stable at room temperature is (a) plastic sulphur (b) amorphous sulphur (c) rhombic sulphur (d) colloidal sulphur (e) monoclinic sulphur
5. Which of the following is the boiling point of sulphur (a) 115(b) 160 (c) 240 (d) 444 (e) 119

ESSAY QUESTIONS

1. State three properties of the element sulphur and outline three uses of sulphur
2. Monoclinic sulphur and rhombic sulphur are the allotropes of sulphur, (i) what are allotropes (ii) name another element which has allotropes
3. Describe what happens when sulphur is heated (i) in the absence of air (ii) in air and the product is dissolved in water. Give the equation of ll reactions involved.
4. (a) What is the atomic number of sulphur (b) name four forms in which sulphur is found in nature?
5. Briefly describe any three allotropes of sulphur (b) put down in tabular form the difference the main difference between rhombic sulphur and monoclinic sulphur.

WEEKEND ASSIGNMENT

Read New School Chemistry for Senior Secondary Schools by Osei Yaw Ababio. Pages 381 -403

PRE READING ASSIGNMENT

Read up compounds of sulphur

WEEKEND ACTIVITY

Describe the stages in the manufacture of H₂SO₄ acid by contact process.

9. Revision.
10. Examination.

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