(a)(i) State the two types of hardness in water.
(ii) Name a salt that causes each type of hardness.
(ii) Write a balanced equation for the removal of each type of hardness.
(iv) State one effect of hard water on soap.
(b)(i) State whether the pH of each of the following is less than, equal to, or greater than 7.
I. Glucose solution II. Chlroine water III. Lime water IV. Sour milk
(ii) Give the difference between the following compounds: I. an acidic oxide and an amphoteric oxide; II. concentrated acid and a dilute acid; Ill. a normal salt and an acid salt
(c)(i) Iron reacts with H\(_2\)SO\(_4\) according to the equation: Fe\(_{(s)}\) + H\(_2\)SO\(_{4(aq)}\) ---> FeSO\(_{4(aq)}\) + H\(_{2(g)}\)
Calculate the mass of FeSO\(_4\) that would be produced by 0.5 mole of Fe. [H = 1, S = 32, Fe = 56]
(ii) List two allotropes of sulphur
(d)(i) State what would La observed when a damp starch-iodide paper is dropped into a gas jar of chloride
(ii) Explain your ansv.er in (d)(i) above.
(iii) State the products formed when ammonia reacts with excess chlorine.
(a) Hardness of water
- (i) Temporary hardness and permanent hardness.
- (ii) Temporary hardness: calcium hydrogen trioxocarbonate (IV), Ca(HCO3)2. Permanent hardness: calcium tetraoxosulphate (VI), CaSO4.
- (iii) Removal of temporary hardness (by boiling):
Ca(HCO3)2(aq) → CaCO3(s) + H2O(l) + CO2(g)
Removal of permanent hardness (by adding washing soda):
CaSO4(aq) + Na2CO3(aq) → CaCO3(s) + Na2SO4(aq) - (iv) Hard water forms an insoluble scum with soap and does not readily form a lather, so it wastes soap.
(b)(i) pH values
- I. Glucose solution: equal to 7.
- II. Chlorine water: less than 7.
- III. Lime water: greater than 7.
- IV. Sour milk: less than 7.
(b)(ii) Differences
- I. An acidic oxide reacts with bases only to form salt and water, while an amphoteric oxide reacts with both acids and bases to form salt and water.
- II. A concentrated acid contains little or no water (a high proportion of acid), while a dilute acid contains a large amount of water (a low proportion of acid).
- III. In a normal salt all the ionizable hydrogen of the acid has been replaced by a metal, while in an acid salt only part of the ionizable hydrogen has been replaced (it still contains replaceable hydrogen).
(c)(i) Mass of FeSO4 from 0.5 mole of Fe
From Fe + H2SO4 → FeSO4 + H2, the mole ratio Fe : FeSO4 is 1 : 1, so moles of FeSO4 = 0.5 mol.
Molar mass of FeSO4 = 56 + 32 + 64 = 152 g mol-1.
Mass = 0.5 × 152 = 76 g.
(c)(ii) Rhombic sulphur and monoclinic sulphur.
(d)(i) The damp starch-iodide paper turns blue-black.
(d)(ii) Chlorine is a stronger oxidizing agent than iodine; it oxidizes the iodide ions on the paper to iodine, and the liberated iodine turns the starch blue-black.
(d)(iii) With excess chlorine, ammonia gives nitrogen trichloride (NCl3) and hydrogen chloride: NH3 + 3Cl2 → NCl3 + 3HCl.
(a) Hardness of water
- (i) Temporary hardness and permanent hardness.
- (ii) Temporary hardness: calcium hydrogen trioxocarbonate (IV), Ca(HCO3)2. Permanent hardness: calcium tetraoxosulphate (VI), CaSO4.
- (iii) Removal of temporary hardness (by boiling):
Ca(HCO3)2(aq) → CaCO3(s) + H2O(l) + CO2(g)
Removal of permanent hardness (by adding washing soda):
CaSO4(aq) + Na2CO3(aq) → CaCO3(s) + Na2SO4(aq) - (iv) Hard water forms an insoluble scum with soap and does not readily form a lather, so it wastes soap.
(b)(i) pH values
- I. Glucose solution: equal to 7.
- II. Chlorine water: less than 7.
- III. Lime water: greater than 7.
- IV. Sour milk: less than 7.
(b)(ii) Differences
- I. An acidic oxide reacts with bases only to form salt and water, while an amphoteric oxide reacts with both acids and bases to form salt and water.
- II. A concentrated acid contains little or no water (a high proportion of acid), while a dilute acid contains a large amount of water (a low proportion of acid).
- III. In a normal salt all the ionizable hydrogen of the acid has been replaced by a metal, while in an acid salt only part of the ionizable hydrogen has been replaced (it still contains replaceable hydrogen).
(c)(i) Mass of FeSO4 from 0.5 mole of Fe
From Fe + H2SO4 → FeSO4 + H2, the mole ratio Fe : FeSO4 is 1 : 1, so moles of FeSO4 = 0.5 mol.
Molar mass of FeSO4 = 56 + 32 + 64 = 152 g mol-1.
Mass = 0.5 × 152 = 76 g.
(c)(ii) Rhombic sulphur and monoclinic sulphur.
(d)(i) The damp starch-iodide paper turns blue-black.
(d)(ii) Chlorine is a stronger oxidizing agent than iodine; it oxidizes the iodide ions on the paper to iodine, and the liberated iodine turns the starch blue-black.
(d)(iii) With excess chlorine, ammonia gives nitrogen trichloride (NCl3) and hydrogen chloride: NH3 + 3Cl2 → NCl3 + 3HCl.
