(a)(i) State one physical method and one chemical method in each case by which the following can be removed:
I. Permanent hardness in water
II. A suspension of CaCO\(_3\) in water.
(ii) Give one disadvantage of hard water.
(b) Explain the following observations: (i) Crystals of washing soda become powdery on exposure to air for a long time
(ii) The concentration of chloride ions in 0.02 mol dm\(^{-3}\) calcium chloride solution is not the same s in 0.02 mol dm\(^{-3}\) sodium chloride solution.
(iii) Iron filings corrode faster than iron nails of the same mass.
(c)(i) Classify each of the following oxides as acidic, basic, neutral or amphoteric. I. ZnO II. CO III. NO\(_2\)
(ii) Give the formula of the acid anhydride of each of the following: I. H\(_2\)CO\(_3\) II. H\(_2\)SO\(_4\)
(iii) Give the IUPAC name of the following salts: I. COCl\(_2\) II. Mg(NO\(_3\))\(_2\).
(d)(i) Mention one pollutant associated with depletion of ozone layer in the atmosphere
(ii) Calculate the volume occupied by 0.125 mole of oxygen at 27°C and a pressure of 2.02 x 105 Nm\(^{-2}\) [I mole of gas occupies 22.4 dm\(^3\) at s.t.p; standard pressure = 1.01 x 105 Nm\(^{-2}\)]
(iii) State one process used for the industrial preparation of oxygen.
(a)(i)
- I. Permanent hardness: physical - distillation (or use of an ion-exchange resin/permutit); chemical - add sodium trioxocarbonate(IV) (washing soda), which precipitates the Ca2+ and Mg2+ ions.
- II. Suspension of CaCO3: physical - filtration (or sedimentation and decantation); chemical - add dilute hydrochloric acid, which dissolves it (\(CaCO_3 + 2HCl \rightarrow CaCl_2 + H_2O + CO_2\)).
(ii) Disadvantage of hard water: it wastes soap (does not lather easily), and it deposits scale (fur) in kettles and boilers.
(b)(i) Crystals of washing soda (Na2CO3·10H2O) lose their water of crystallization to the air on long exposure and become powdery. This is efflorescence.
(ii) Each CaCl2 gives 2 chloride ions while each NaCl gives only 1, so 0.02 mol dm-3 CaCl2 has \([Cl^-] = 0.04\) mol dm-3 whereas 0.02 mol dm-3 NaCl has \([Cl^-] = 0.02\) mol dm-3 - twice as concentrated in chloride.
(iii) Iron filings have a much larger surface area exposed to air and moisture than nails of the same mass, so they rust (corrode) faster.
(c)(i) I. ZnO - amphoteric; II. CO - neutral; III. NO2 - acidic.
(ii) Acid anhydride: I. H2CO3 → CO2; II. H2SO4 → SO3.
(iii) IUPAC names: I. CoCl2 - cobalt(II) chloride; II. Mg(NO3)2 - magnesium trioxonitrate(V).
(d)(i) Pollutant depleting the ozone layer: chlorofluorocarbons (CFCs).
(ii) At s.t.p. 0.125 mol of O2 occupies \(0.125 \times 22.4 = 2.8\ \text{dm}^3\).
\[V_2 = V_1 \times \frac{P_1}{P_2} \times \frac{T_2}{T_1} = 2.8 \times \frac{1.01 \times 10^5}{2.02 \times 10^5} \times \frac{300}{273}\]
\[V_2 = 2.8 \times 0.5 \times 1.099 = 1.54\ \text{dm}^3\]
(iii) Industrial preparation of oxygen: fractional distillation of liquefied air.
(a)(i)
- I. Permanent hardness: physical - distillation (or use of an ion-exchange resin/permutit); chemical - add sodium trioxocarbonate(IV) (washing soda), which precipitates the Ca2+ and Mg2+ ions.
- II. Suspension of CaCO3: physical - filtration (or sedimentation and decantation); chemical - add dilute hydrochloric acid, which dissolves it (\(CaCO_3 + 2HCl \rightarrow CaCl_2 + H_2O + CO_2\)).
(ii) Disadvantage of hard water: it wastes soap (does not lather easily), and it deposits scale (fur) in kettles and boilers.
(b)(i) Crystals of washing soda (Na2CO3·10H2O) lose their water of crystallization to the air on long exposure and become powdery. This is efflorescence.
(ii) Each CaCl2 gives 2 chloride ions while each NaCl gives only 1, so 0.02 mol dm-3 CaCl2 has \([Cl^-] = 0.04\) mol dm-3 whereas 0.02 mol dm-3 NaCl has \([Cl^-] = 0.02\) mol dm-3 - twice as concentrated in chloride.
(iii) Iron filings have a much larger surface area exposed to air and moisture than nails of the same mass, so they rust (corrode) faster.
(c)(i) I. ZnO - amphoteric; II. CO - neutral; III. NO2 - acidic.
(ii) Acid anhydride: I. H2CO3 → CO2; II. H2SO4 → SO3.
(iii) IUPAC names: I. CoCl2 - cobalt(II) chloride; II. Mg(NO3)2 - magnesium trioxonitrate(V).
(d)(i) Pollutant depleting the ozone layer: chlorofluorocarbons (CFCs).
(ii) At s.t.p. 0.125 mol of O2 occupies \(0.125 \times 22.4 = 2.8\ \text{dm}^3\).
\[V_2 = V_1 \times \frac{P_1}{P_2} \times \frac{T_2}{T_1} = 2.8 \times \frac{1.01 \times 10^5}{2.02 \times 10^5} \times \frac{300}{273}\]
\[V_2 = 2.8 \times 0.5 \times 1.099 = 1.54\ \text{dm}^3\]
(iii) Industrial preparation of oxygen: fractional distillation of liquefied air.
