QUESTIONS AND PROBLEMS 121 



51. State whether sulphur is found in the free state in nature and where. 



Mention some native metallic sulphides. What is meant by a 

 "double" sulphide? 



52. When iron is treated with dilute acid, hydrogen gas is evolved. 



When sulphide of iron is treated in the same way, what gas is then 

 produced ? What is the composition of this gas by weight ? 

 Express by a formula. 



53. When organic matter containing sulphur decays, what is the product 



of decomposition ? To what is the smell of Harrogate water due ? 



54. What is meant by saying that one element can " replace" another in 



a chemical compound ? Give examples. 



55. What is the product of the combustion of sulphur? Express its 



composition by a formula. W^hen dissolved in water, what com- 

 pound is produced ? 



56. What evidence is there that sulphurous acid becomes changed into 



sulphuric acid by atmospheric oxidation ? 



57. Under what conditions does sulphurous anhydride combine with 



oxygen to form sulphuric anhydride? Illustrate your answer by 

 a drawing of the apparatus that may be used, and express the 

 reaction by an equation. Explain the term "contact action." 



58. Would you regard sulphurous acid as a "stable" or an "unstable" 



compound, and why ? 

 •■59. Distinguish the metal from the metallic sulphide. (Iron and sulphide 



of iron.) 

 ^60. Identify the powders. (Sulphur and quicklime.) 



Sulphuric Acid. 



61. In what proportion does sulphuric anhydride combine with water 



forming sulphuric acid ? Is the oil of vitriol of comn-.erce pure 

 sulphuric acid ? 



62. What evidence is there that sulphuric acid itself combines with water ? 



What practical use is made of this ? 



63. Describe fully the method of determining the proportions in which 



caustic soda and sulphuric acid react to form a neutral salt. 

 What is the result obtained ? 



64. Express the neutralisation of caustic soda and sulphuric acid by an 



equation, and state how it was proved that water was set free in 

 quantity corresponding with the equation. 

 *(i<i. Determine the strength of the sulphuric acid solution by means of 

 caustic soda or caustic potash. 



