The Chemical Relations of Water 305 



QUESTIONS 



1. A jar of gas is supplied to you. By what tests would you 

 attempt to find out whether the gas was one of the following : 

 hydrogen, carbon dioxide, oxygen ? 



2. A reducing agent may be briefly defined as a substance 

 which readily combines with the oxygen of a compound, leaving 

 another substance with a lesser proportion of oxygen. Give reasons 

 for considering hydrogen to be a reducing agent. 



3. Describe any experiments you know which illustrate the 

 energetic nature of the combination of hydrogen and oxygen. 



4. Briefly describe the experiments necessary to distinguish 

 clearly between distilled water, river water, and sea water. 



5. How may the composition of water by weight be deter- 

 mined ? What weight of water would contain 67 '9 g. of oxygen ? 



6. Why do lakes and rivers not become frozen solid during long 

 spells of frosty weather ? 



7. A certain liquid leaves no residue on evaporation to dryness. 

 What further evidence would you require to be presented before 

 deciding whether it is water ? 



8. Describe a method of obtaining oxygen from the air by a 

 process not involving chemical change. 



9. 15*6 c.c. of oxygen are mixed with 8'75 c.c. of hydrogen 

 in the tube of the eudiometer, and a spark is passed through the 

 mixture. What volume of gas is left, and what is its nature? 



10. What alterations of volume occur during the change of 

 a quantity of ice at 5 into steam at 105 ? 



11. For what reason is it necessary to dry the hydrogen used 

 in Experiment 134 ? 



12. Describe all that is seen when a lighted taper is thrust 

 upward into a dry jar of hydrogen. 



13. What is a reversible reaction ? Describe experiments which 

 show that the oxidation of mercury is of this character. Specify 

 clearly the conditions requisite for each phase of the action to take 

 place. 



H. D. s. 20 



