SECOND TERM E-LEARNING NOTES SUBJECT: CHEMISTRY CLASS: SS 2 SCHEME OF WORK

SECOND TERM E-LEARNING NOTES

SUBJECT: CHEMISTRY CLASS: SS 2

SCHEME OF WORK

WEEK TOPICS

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.[mediator_tech]

WEEK 1: Revision of last term’s work.

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 H₂O₂ and 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 2p⁶3s²3p⁴

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

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Electronic configuration of sulphur

EVALUATION

Enumerate any five (5) general properties of group VIA elements.
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.

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

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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 96 and 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

c. 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)

d. 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

(a) What is allotropy? (b)(i) Name two allotropes of sulphur (ii) State two differences between them.

Explain briefly, how Rhombic and monoclinic sulphur are obtained.
Describe the formation of plastic sulphur and amorphous sulphur.

PROPERTIES OF SULPHUR

PHYSICSL PROPERTIES

Sulphur is a yellow solid existing in crystalline or amorphous
It is non-metallic and exhibits allotropy.

It sublimes to give flowers of sulphur.
It is a non-conductor of heat and electricity.
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

Used in the production of tetraxosulphate (VI) acid.
Used in vulcanizing rubber. It makes raw rubber to become hard, tough and elastic and hence, suitable for making tyres
Used in the production of carbon (iv) sulphide used as a solvent and insecticides

It is used in gun powder and matches, dyes tuffs fungicides, ointment and germicides
Also used in the production of calcium hydrogen trioxosulphate (iv), Ca(HSO₃)₂ used in bleaching wood pulp for making news prints

EVALUATIONs

(a) What is flower of sulphur (b) what are the products of reaction of sulphur with it concentrated H₂SO₄ acid
Mention three(3) physical and four (4) chemical properties of sulphur
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) + SO₂ _(g) + H₂O_(l)

(a) SO₂ _(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 is a colourless liquid, which smells strongly of SO₂.

2. It turns blue litmus paper red.

It mixed readily with water.

It has an irritating and choking smell.

CHEMICAL PROPERTIES OF TRIOXOSULPHATE (IV) ACID

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)

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

It is used for bleaching.

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

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.[mediator_tech]

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

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)}

When exposed to air trioxosulphate (IV) salts are slowly oxidised to tetraoxosulphate (VI) salts.

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.

BaCl₂ _(aq) + Na₂SO_{3 (aq)}→ BaSO_3(s) + 2NaCl _(aq)

TEST FOR TRIOXOSULPHATE (IV) SALT

On warming with dilute hydrochloric acid sulphur (IV) oxide is given off.
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.

BaCl₂ _(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:

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)

The absorption of sulphur (VI) oxide, SO₃in conc. H₂SO₄ to form a fuming liquid called ‘Oleum’- heptaoxosulphate (VI) acid.

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

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

As an acid – H₂SO₄ is 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)

Action of dilute H₂SO₄ on 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.

Action on trioxocarbonate(IV) ,Carbon(IV) oxide is liberated when H₂SO₄ is 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.

Conc. H₂SO₄ as 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 SO₂ in 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.

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.H₂SO₄ is hygroscopic, that is, it absorbs water from the air and becomes dilute. When conc. H₂SO₄ is 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

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

GENERAL EVALUATION

OBJECTIVE TEST:

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[mediator_tech]
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 H₂SO₄ acid
Mono clinic and Rhombic are allotropes of (a) carbon (b) oxygen (c) Neon (d) Polonium (e) sulphur
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
Which of the following is the boiling point of sulphur (a) 115 (b) 160 (c) 240 (d) 444 (e) 119

ESSAY QUESTIONS

State three properties of the element sulphur and outline three uses of sulphur
Monoclinic sulphur and rhombic sulphur are the allotropes of sulphur, (i) what are allotropes (ii) name another element which has allotropes
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.
(a) What is the atomic number of sulphur (b) name four forms in which sulphur is found in nature?
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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