1 30 CHE MIS TR V FOR A GRIC UL TCRA L S TUDENTS 



175. Mention some of the important metallic carbonates occurring in 



nature. In what geological forms does carbonate of calcium 

 exist, and how is lime obtained from them on the large scale ? 



1 76. What is meant by dissociation ? Illustrate your answer by examples, 



and give examples of chemical decomposition which are not 

 cases of dissociation ? 



177. What is mortar, and why does it "set"? What are "hydraulic" 



cements, and what is the cause of the " setting " of these ? 



1 78. Express the composition of carbonate aud bicarbonate of sodium by 



formulae. State whether the carbonates of the alkali metals 

 (including ammonium) are soluble in water, and whether any 

 other metallic carbonates are soluble. State also whether the 

 alkaline carbonates can be dissociated by heat, and whether 

 carbonates of other classes of metals resist dissociation. 



1 79. What evidence is there for the existence of carbonic acid ? Has it 



ever been obtained in the pure state ? What other unstable acids 

 does carbonic acid resemble in composition and properties ? 



180. What would be the effect of mixing together the soluble phosphate 



of calcium and chalk ? Illustrate by an equation. 



181. When carbonic acid gas is passed into water containing suspended 



chalk, the chalk dissolves. To what is this due ? What happens 

 when the liquid is boiled or mixed with an alkali ? 



182. To what is the hardness of spring water due ? Why is the hardness 



sometimes called "temporary," sometimes "permanent"? How 

 may water, both temporarily and permanently hard, be softened ? 

 Illustrate by equations. 



183. Describe the properties of carbonate of ammonium. What occurs 



when solutions of carbonate of ammonium and gypsum are mixed 

 together, and when dry sulphate of ammonium and chalk are 

 warmed together ? Explain the reason of the occurrence of both 

 reactions. 



*i84. By titrating with standardised sulphuric acid, determine whether the 

 salt is carbonate of potassium or carbonate of sodium. 



^185. Determine the percentage of carbonate in the bicarbonate by 

 strongly heating a weighed quantity till no further loss in weight 

 occurs. 



*i86. Estimate the carbonates in the tap water by means of standardised 

 sulphuric acid. Express the result as milligrams of calcium 

 carbonate per liter. 



*i87. Identify the salts of calcium. (Calcium sulphate, bleaching powder, 

 calcium phosphate, calcium dihydrogen phosphate, calcium car- 

 bonate, calcium silicate, calcium choride.) 



