QUESTIONS AND PROBLEMS 45 



Oxygen Gas. 



19. Of the red oxides of iron, lead and mercury and the black oxide of 



copper, which yield oxygen on heating, and what are the residues 

 left when oxygen ceases to be evolved ? 



20. Fully describe a method for preparing a bottle of pure oxygen gas. 



Illustrate your description by a drawing of the apparatus used. 



2 1 . Compare the properties of oxygen and nitrogen. 



22. Describe the combustion of phosphorus, sulphur, charcoal, and iron 



in oxygen gas. Of each product describe the appearance and 

 smell. Is it a solid or a gas ? Is it soluble in water and is the solu- 

 tion acid in reaction ? 



23. Judging from the examples dealt with so far, what appears to be the 



relation of heat towards (i) chemical change in general, (2) chemical 

 combination, and (3) chemical decomposition ? 



24. Describe minutely how the composition of red oxide of mercury by 



weight may be determined, and state the amount of oxygen existing 

 in this compound combined with 100 grams of mercury. 



^25. Identify the metallic oxide (red oxide of iron, red oxide of mercury or 

 red lead). 



*26. Prepare a bottle full of oxygen gas. 



Carbonic Acid Gas. 



27. In what proportion does carbonic acid gas exist in the air? How may 



its presence be demonstrated, and to what is it due ? 



28. Describe a method for preparing carbonic acid gas. 



29. Give the properties of the gas. Does it support combustion ? Is it 



soluble in water, and if so, what is the action of the solution on 

 litmus? Is the gas heavier or lighter than air, and how does it 

 behave to lime water and solution of potash ? 



30. Fully describe the method of determining the composition of carbonic 



acid gas, and state in what proportions carbon and oxygen are 

 combined in this compound. 



31. Why should the ventilation of rooms be necessary? In your reply 



state to what the vitiation of air is due, to what extent may the 

 composition of air in rooms be altered, and what is the effect upon 

 the health of breathing vitiated air. 



32. State what you know about the diffusion of gases. How may this 



principle be utilised in ventilation ? 



33. What is the effect of heat upon the volume of a gas, and how may this 



effect be utilised in promoting ventilation ? 

 *34. Identify the gas (oxygen, nitrogen, carbonic acid gas, or air). 



