(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.
Explanation
(a) Removal of permament hardness in water (i) Physical method - by distillation. Chemical method - addition of washing soda and the use of ion-exchange resin. (ii) Removal of CaCO\(_3\) Physical method ---Filtration. Chemical method - Bubbling CO\(_2\) into the mixture for a long time or addition of an acid. (ii) Disadvantages of hard water - Waste soap - causes furring in pans and kettles - results in burst pipe narrow tubes in boilers.
(b)(i) The crystals lose their water of crystallization to the atmosphere. (ii) Each mole of CaCl\(_2\) ionizes to give two moles of Cl\(^-\) - whereas one mole of NaCl produces one mole of CL\(^-\) on ionization. (iii) With the iron filings, a greater surface area is exposed than in the nails and since raa increases with increase in surface area.
(c)(i) (i) Amphoteric oxides - ZnO (ii) Neutral oxide - CO (iii) Adidic oxide - NO\(_2\) (ii) (i) Acid Anhydride (H\(_2\)CO\(_3\)) is CO\(_2\) (ii) Acid Anhydride (H\(_2\)SO\(_4\)) is SO\(_3\) (iii) COCl\(_2\) is cobalt (II) chloride Mg(NO\(_3\))\(_2\) is magnesium trioxonitrate (V)
(d)(i) Chlorofluorocarbon are aerosols etc. (ii) 1 mole of O\(_2\) occupies 22.4 dm\(^3\) at s.t.p; 0.125 mole O\(_2\) occupies (22.4 x 0.125) dm\(^3\) at s.t.p. from \(\frac{P_1V_1}{T_1}\) = \(\frac{P_2V_2}{T_2}\) = 28 dm\(^3\) = \(\frac{28 \times 1.01 \times 10^5}{273}\) = \(\frac{v^2 \times 2.02 \times 10^5}{300}\) \(v^2 = \frac{2.8 \times 1.01 \times 300}{273 + 2.02} = 154dm^3\)
(iii) Fractional distillation of liquid air or electrolysis of water
