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
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
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
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 2p6 3s23p4
The distribution of electrons into shell is given in the figure below:
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.
- 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
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 119oC 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) + O2(g) → 2H2O(g) + S(g)
S2O32-(aq) +2H+(aq) → 2H2O(l) + SO2(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) + O2(g) → SO2(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) → CS2(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) + H2SO4(aq) → 2H2O(l) + 3SO2(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) Na2SO3(s) + 2HCl(aq) → 2NaCl(qg) + SO2 (g) + H2O(l)
(a) SO2 (g) + H2O (l) → H2SO3 (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) + H2SO3 (aq) → Na2SO3 (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. H2SO4(aq) + O2(g) →2H2SO4(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.
H2SO3 (aq) + NaOH (aq) → Na2SO3(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.
SO2 (g) +2H2O (l) +ZNNO3 (ag) → ZnSO3(s) +HNO3 (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,
Na2CO3 (aq) + 2HCl (aq) → 2NaCl (aq) + H2O (l) +SO2 (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) + Na2SO3 (aq) → BaSO3(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. Na2SO3.
BaCl2 (aq) + Na2SO3 (aq) → 2NaCl (aq) + BaSO3(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
2SO2(g) + O2 2SO3(g)
- The absorption of sulphur (VI) oxide, SO3 in conc. H2SO4 to form a fuming liquid called ‘Oleum’- heptaoxosulphate (VI) acid.
H2SO4(aq)+ SO3(g)→ H2S2O7(aq)– oleum
- The oleum is diluted with correct amount of water to produce the conc. H2SO4.
H2S2O7(aq)+ H2O(l)→ 2H2SO4(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)+ H2SO4(aq)→ Na2SO4(aq)+ 2H2O(l) and
NaOH(aq)+ H2SO4(aq)→ NaHSO4(aq)+ H2O(l)
- Action of dilute H2SO4 on metals Reactive metals would displace hydrogen from dilute tetraoxosulphate(VI) acid.
Zn(s)+ H2SO4(aq)→ ZnSO4(aq)+ H2(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).
Na2CO3(aq)+ H2SO4(aq)→ Na2SO4(aq)+ H2O(l)+ CO2(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)+ 2H2SO4(aq)→ 2H2O(l)+ 3SO2(g)
C(s)+ 2H2SO4(aq)→ 2H2O(l)+ 2SO2(g)+ CO2(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.
C12H22O11(s) + nH2SO4(l)→ 12C(s)+ 11H2O(l)+ nH2SO4(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.
BaCl2(aq)+ Na2SO4(aq)→ 2NaCl(aq)+ BaSO4(s)
Ba(NO3)2(aq)+ Na2SO4(aq)→ 2NaNO3(aq)+ BaSO4(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.