7. a) Name two elements which are liquid at ordinary temperatures, {h) Name 



the common allotropic forms of each of four elements, (c) Name two 

 elements having exceptionally high melting-points, and state how this 

 property is put to practical use in case of each. 



8. a) Describe briefly an experiment to determine the percentage of oxygen in 



air. {h) State as fully as possible the composition of air. (c) Give 

 three proofs that air is a mixture and not a compound. 



9. a) State one point of resemblance and one point of difference between solu- 



tions and compounds. 



b) Define precipitation and crystallization; illustrate each by means of an 



example. 



c) How are the freezing-point and the boiling-point of a solvent affected by 



dissolved substances ? Give a practical application of one of these facts. 



10. a) Distinguish between chemically pure water and spring water, {h) How 



may water be purified on a small scale for household use ? How is it 

 purified on a large scale for a city supply? (c) Name one impurity 

 which renders water unfit for use in laundries and outline a practical 

 method for removing it. 



11. a) Define the terms hydroxide, anhydrous, and water of hydration (crystal- 



hzation). 

 h) Show that hydration is a reversible reaction by discussing the commercial 

 manufacture and use of plaster of Paris. 



12. a) Describe the manufacture of sulphuric acid by the contact process. 



b) Show how sulphuric acid is used to produce another acid, and state the 



principle involved. 



c) Write the ionic equation for neutralizing barium hydroxide with sulphuric 



acid. 



13. Make a list of five gases which would be dangerous to life if contained in air 



to the extent of a small per cent, and suggest a method of eliminatmg 

 each gas. Only a single impurity is assumed present in any one of the 

 given samples of air. 



14. a) How may crude copper be refined ? {b) State the physical and chemical 



properties of copper. Write an equation showing the action of hot, 

 concentrated sulphuric acid upon the metal, (c) Name the elements 

 present in important alloys of copper. 



15. State one locality in which each of the following substances, respectively, is 



found in relative abundance: iron ore, diamond, petroleum, sodium nitrate, 

 sulphur, gold, copper ores, phosphate rock, coal, radium compounds. 



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