QUESTIONS AND PROBLEMS 49 



Hydrogen Gas. 



75. Describe two methods for preparing hydrogen gas. 



76. Compare the properties of hydrogen, in respect to combustibihiy, 



smell, colour, solubility and density, with oxygen, nitrogen, and 

 carbonic acid gas. 



77. Give an account of the method for determining the relative density of 



hydrogen. 



78. Calculate the relative density of a gas (hydrogen = i) from the 



following data : — 

 Capacity of flask = 980 c.c» 



Weight of flask and air at 15° C. and 760 m.m. = 88.303. 

 Weight of flask and gas at the same temperature and 



pressure = 88.407. 

 A liter of air at 15° C. and 760 m.m. weighs 1.226 grams. 

 The relative density of hydrogen (air = 1) is .069. 



79. To what extent do gases expand when heated ? What would 10 c.c. 



of a gas at 0° C. measure at 100° C, and what would 15 c.c of a 

 gas at 15° C. measure at - 5° C. ? 



80. To what extent do gases expand or contract under variations of 



pressure ? What would a liter of air under the normal atmospheric 

 pressure measure under a pressure of 90 inches of mercury (3 

 atmospheres) ? 



81. What weight of air would a liter flask hold at a temperature of 20° C. 



and a pressure of 29 inches of mercury ? 



82. Give an account of the determination of the composition of water by 



weight, and illustrate by a drawing the apparatus used. Refer 

 especially to all the precautions that must be taken to obtain a 

 correct result. 

 *%'}i' Prepare a bottle full of pure hydrogen gas. 



Conclusions. 



84. Distinguish between the sciences of physics and chemistry. Give 



examples of physical and chemical change. 



85. Distinguish between the two kinds of chemical change, and illustrate 



each kind by examples. Point out how in the action of steam on 

 heated iron, and of hydrogen on heated copper oxide, both kinds of 

 chemical change take place simultaneously. 



86. Discuss the relation of heat to chemical change. 



%"]. What are the two available methods for investigating the composition 

 of matter ? 



