HYDROCHLORIC ACID. CALCULATIONS 137 



Observe that the atomic weights are multiplied by the sub-num- 

 bers, so that, for example, Fe s = 3 X 55.84. Observe also that 

 the formula weights are multiplied by the coefficients, when such 

 occur, in front of the formula, so that, for example, 4H 2 = 4 

 X 18.016. 



The proportion 231.52 : 8.064 :: 45 : x (= 1.57) supplies the 

 answer, 1.57 grams of hydrogen. 



Using the alternative plan (p. 130): If 231.52 g. of magnetic 

 oxide are reduced by 8.064 g. of hydrogen, 1 g. will be reduced 



8.064 

 by ' g. ( = 0.035 g.) of hydrogen. Hence, if 1 g. of magnetic 



ZoL.oZ 



oxide is reduced by 0.035 g. of hydrogen, 45 g. will be reduced by 

 45 X 0.035 g. (= 1.57 g.) of hydrogen. 



Exercises. 1. Complete the equation ZnCl 2 + H 2 S0 4 > 

 ZnSO 4 + , and attach the name of the substance to each for- 

 mula in it. 



2. Point out the differences in physical properties between 

 oxygen and hydrogen chloride. 



3. Make equations for the displacement of hydrogen from 

 hydrochloric acid by zinc and by sodium (pp. 51 and 52). 



4. Give additional examples of the four varieties of chemical 

 change (p. 132). 



5. Classify (p. 132) the following actions: (a) the action of 

 steam on iron (p. 51); (b) the rusting of iron; (c) the electrolysis 

 of dilute hydrochloric acid (p. 55); (d) the effect of heating the 

 hydrate of cupric sulphate (p. 68). 



6. Is the decomposition of mercuric oxide a case of: (a) dis- 

 sociation, or (b) oxidation or reduction? 



7. What is the proportion of: (a) sodium to one part of chlorine 

 in salt; (b) one part of hydrogen to nitrogen in nitric acid (HN0 3 )? 



8. Calculate the percentage composition of: (a) sulphuric 

 acid; (b) acetylene C 2 H 2 . 



9. What weight of hydrogen is displaced by the action of 100 g. 

 of zinc upon an excess of hydrochloric acid (ZnCl2 is formed)? 



