7- State in words and by writing equations how you would obtain: (a) Ferric 

 chloride from ferrous chloride; (b) ferrous chloride from ferric chloride; 

 (c) sodium carbonate from sodium hydroxide; (d) sodium hydroxide from 

 sodium carbonate; (e) oxygen from ozone; (/) ozone from ox^'gen. 



8. How would you prove, by chemical means, the presence in air of each of the 



following components: (a) water, (b) carbon dioxide, (c) oxygen, (d) nitro- 

 gen? 



9. a) Arrange the names of ten common elements in natural groups. 



b) Write the formula for one oxide of each and state what acid or base can 

 be formed from each of these oxides. 



Group B 



(Answer two questions from this group.) 



10. a) A compound has the following composition: carbon, 54.67 per cent; 



hydrogen, 9. 11 per cent; oxygen, 36.22 per cent. Find the simplest 

 formula for the substance. (C = i2, 0=i6, H=i.) 

 b) A body of air at constant pressure occupies a volume of 500 c.c. at 20° C. 

 At what temperature will its volume become 1,000 c.c. ? 



11. How many liters of ammonia gas, measured under standard conditions, can 



be obtained when 20 gm. of sodium hydroxide react with an excess of 

 ammonium sulphate? (Xa = 23, 0=i6, H = i, N=i4, 8 = 32.) 

 Note. — A liter of ammonia gas at o°C. and 760 mm. weighs 0.772 gm. 



12. What experimental evidence can be cited to show (a) that chloride ions are 



not molecules of chlorine ? {b) that chloride ions are charged with nega- 

 tive electricity ? 



13. Write a reversible chemical reaction and explain how it may be made to go 



to completion in either direction. 



Group C 

 {Answer one question from this group.) 



14. a) Make a diagram of an acetylene generator. With the aid of an equation, 



explain its operation. 



b) Write the equation for the complete combustion of acetylene. 



c) Why does acetylene burn with a flame which is more luminous than 



that of methane ? 



15. Answer any two of the following questions: 



c) Mention a necessary property that must be possessed by an oil (i) for 

 soap-making, (2) for mixing with paint, (3) for a lubricant. Name as 

 an example some particular oil for each use. 



b) What are the physical and chemical differences between cast iron and 



steel ? 



c) Why does iron, in the course of time, turn completely into rust, while 



aluminium and zinc tarnish only slightly ? 



41 



