1 The reaction is as follows: Mg(s) + H2SO4(aq) → MgSOâ€‹4(aq) + H2(g) 1 mole of Mg gives 1 mole H2 2 Moles of H2 obtained: 24000 cc is the volume of 1 mole of gas at STP 1 cc is the volume of 124000 mole of gas 298 6 cc is 124000×298 6=0 012 moles of H2 3 0 012 moles of H2=0 012 moles of Mg mass of Mg = number of moles×molar mass=0 012×24 3 =0 319 4 Percent purity = 0 3191×100=31 99%

11

11 IAns. 8 molesl 4. Zinc blende 17.nSl is roasted in air. Calculate : al the number of moles of sulphur dioxide liberated by 776 g of 7.nS and b,' The weight of ZnSrequired to produce 22.4 at s.t.p, Is-32, zn-65, 0-161 tAns.97g.1 5. Ammonia reacts with sulphuric acid to give the fertilizer ammonium sulphate. Calculate thevolume oi ammonia lat s. t.p.J used to form 59 g of ammonium sulphate. [ N-14. 1--1-1, S-32, 0-161. 6. Heaton lead nitrate gives yellow lead (Ill oxide, nitrogen dioxide & oxygen. Calculatethetotal volume of N02 & 02 produced on heating 8.5 of lead nitrate. [T'b 207, N = 14. O = 161. IAns. 1.15 of N02 & 0.287 of 02 (1.437 Its.)l • 7. +302; Calculate the amount of KC103 which on thermal decOmposition gives 'X' vol. of 02,' which is the volume required for combustion of 24 . of carbon. .163.33g.1 [K = 39, Cl = 35.5, 0=16, C = 12]. 8. Calculate the weight of ammonia gas. al Required for reacting with sulphuric acid to give 78 g. of fertilizer ammonium sulphate. bl Obtained when 32.6 g. of ammonium chloride reacts with calcium hydroxide during the laboratory preparation of ammonia. [2NH4Cl + CaC12 + 2H20 + 2NH31 [Ans.a) 20.09 g. b) 10.36 g.l [N = 14, H = 1, 16, s = 32, Cl = 35.51. 9. Sodium carbonate reacts with dil. H2S04 to give the respective salt, water and carbon dioxide. Calculate the mass of pure salt formed when 300 g. of Na2C03 of 80% purity reacts with dil. H2S04. [Ans. 321.51 g.l 12, 16, H = 321. 10. Sulphur burns in oxygen to give sulphur dioxide. If 16 g. of sulphur burns in 'x' cc. of oxygen, calculate the amount of potassium nitrate which must be heated to produce 'x' cc. of oxygen. [S -32, K = 39, N =14, 0=16]. [Ans. 1018.1 'I. Sample of impure magnesium is reacted with dilute sulphuric acid to give the respective salt and hydrogen. If 1 g. of the impure sample gave 298.6 cc. of hydrogen at s.t.p. Calculate the % purity of the sample. [Mg = 24, H = 11. (Ans. 31.990/01 96

1. The reaction is as follows:

Mg(s) + H₂SO₄(aq)

\to

MgSO₄(aq) + H₂(g)

1 mole of Mg gives 1 mole H₂

2. Moles of H₂ obtained:

24000 cc is the volume of 1 mole of gas at STP
1 cc is the volume of

\frac{1}{24000}

mole of gas
298.6 cc is

\frac{1}{24000} \times 298.6 = 0.012 m o l e s

of H₂

3. 0.012 moles of H₂=0.012 moles of Mg
mass of Mg =

n u m b e r o f m o l e s \times m o l a r m a s s = 0.012 \times 24.3

=0.319

4. Percent purity =

\frac{0.319}{1} \times 100 = 31.99 %

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