QUESTIONS AND ANSWERS 13 



39 -f- 35 + 48 = 122, the molecular weight of KCIO3. 



48 ~ 122 = .393, the percentage composition of oxygen. 

 10 grammes of KCIO^ would contain 3.93 grammes of oxygen. 

 Calculate the weight of carbonic acid gas that can be obtained from 



one pound of marble. Write the equation. [Atomic wt. 



of Ca = 40, of O = 16, of C = 12.J 

 CaCOj + heat = CaO + CO^. 



40 + 12 + 48 = 100, the molecular weight of calcium carbonate 

 (marble). 12 + 32 = 44, the molecular weight of carbon dioxide 

 (carbonic acid gas). Therefore .44 is the percentage composition 

 of CO2. From one pound of marble, .44 of a pound of CO^ could 

 be obtained. 



Under standard conditions how many litres of hydrochloric acid will 



result from the action of sulphuric acid on 117 grammes of 



common salt? [Na = 23, CI = 35.5.] 



2NaCl + H,SO, = Na^SO, + 2HC1. The molecular weight of 



NaCl = 58.5. The molecular weight of HCl = 36.5. 58.5 : 36.5 = 



117 : X. X = 73g. One litre of hydrogen weighs 0.0899 gramme 



under standard conditions. 73 -^ 0.0899 = 812 litres. 



How much chlorine can be derived from 50 grammes of NaCl? 

 [Atomic weight of Na = 23, of CI = 35.5.] 

 23 + 35.5 = 58.5, the molecular weight of NaCl. 35.5 : 58.5 = 

 X : 50. X = 30.34 grammes. 



HYDROGEN 



What are the physical and chemical properties of hydrogen? 



Hydrogen, the lightest of all elements, is a colorless, odorless, 

 tasteless gas ; combustible, burning with a colorless flame, but is not 

 a supporter of combustion. The resulting compound of its com- 

 bustion in air is water. It is only slightly soluble in water, is 

 electropositive and capable of combining with many elements. 



Give details of the preparation of hydrogen by the action of an acid 

 on a metal. Write the equation. 



Place a quantity of granulated zinc in a glass flask and cover 

 it with dilute hydrochloric acid. Adjust a piece of glass tubing in 

 the stopper of the flask and after the air of the flask is expelled, 

 hydrogen will pass from the tubing. Zn -j- 2HC1 = ZnClg + 2H. 



Give (a) the symbol, (b) valence, (c) atomic weight, and (d) a method 

 of preparation of hydrogen. 



(a) H, (b) 1, (e) 1, (d) see answer to preceding question (Iron 



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