(a)(i) Determine the oxidation number of sulphur in Na\(_2\)S\(_2\)O\(_3\)
(ii) Name the allotropes of sulphur.
(iii) State two ways in which the structure of graphite and diamond are similar.
(b)(i) Name two green-house gases.
(ii) State one effect of an increased level of green-house gases on the environment.
(iii) State one source from which nitrogen (I) oxide is released into the environment.
(iv) Write a chemical equation to show the effect of heat on each of the following compounds: I. KNO\(_{3(s)}\) II. AgNO\(_{3(s)}\)
(C)(i)Describe briefly how pure crystals of calcium chloride could be obtained from a solution of calcium chloride
ii) Explain briefly each of the following observations:
I. ammonia gas is highly soluble in water;
II. boiling ploint of chlorine is lower than that of iodine
(d) Consider the reaction represented by the following equation:- 2NaCl + H\(_2\)SO\(_{4(s)}\) \(\to\) Na\(_2\)SO\(_{4(s)}\) + 2HCl\(_{(g)}\)
Calculate the volume of HCl gas that can be obtained at s.t.p. from 5.85 g of sodium. chloride. [ Na = 23.0, Cl = 35.5, Molar volume of gas at s.t.p. = 22.4 dm\(^3\)]
Explanation
(a) (i) let x = oxidation number of sulphur 2(1) + 2 + 3(-2) = 0
x = +2
(ii) Allotropes of sulphur are: – rhombic / alpha sulphur. – monoclinic / Beta / prismatic sulphur. – amorphous / delta sulphur. – plastic sulphur
(iii) – Macromolecule / giant molecule /3 dimensional. – carbon atoms are covalently bonded. – crystalline in nature.
(b) (i) Carbon(IV)oxide. – methane. – nitrogen(I)oxide. –water vapour – ozone – chlorofluorocarbons.
(ii) – Global warming / climate change.
(iii) – Ammonium trioxonitrate (V) /aerosol (accept ammonium nitrate). – Combustion of fuel at high temperature.
(iv)
(I) 2KNO\(_3\) --> 2KNO\(_2\) + O\(_2\)
(II) 2AgNO\(_{_3(s)}\) ---> 2Ag\(_s\) + 2NO\(_{2(g)}\) + O\(_2\)
(c) (i) – Heat the solution to concentrate it or leave in a warm place.
- partially evaporate solution and allow to cool filter off crystals.
- pick out crystals
- Dry crystals with filter paper.
(ii)(1) Ammonia readily associates with water molecules through hydrogen bonding.
(II) Chlorine molecules are smaller or chlorine molecules have fewer number of electrons and the strength of van der waals forces between molecules are weaker as compared to that of iodine OR iodine molecules are higher and the wander waal's forces between molecules are stronger as compared to that of chlorine.
(d) Mr(NaCl) = 23.0 + 35.5 = 58.5g/mol\(^1\)
Mass of NaCl = 5.85g
Molar mass of NaCl= 58.5g/mol\(^1\)
Amount of NaCl in 85g = \(\frac{5.85g}{58.5gmol^{-1}}\) = 0.1mol
1 mol of NaCI = 22.4dm\(^3\) of HCI
:. 0.1 mol = \(\frac{0.1}{1}\) x 22.4 = 2.24dm\(^3\)
OR
Molar mass NaCl = 23.0 + 35.5 = 58.5gg/mol\(^1\)
58.5g of NaCl = 22.4dm\(^3\) HCl
58.5g = \(\frac{22.4}{58.5}\) x 5.85
= 2.24dm\(^3\)