176 JUNIOR GRADE SCIENCE 



138. How is chalk distinguished from lime ? Name the elements present 

 in chalk. If you are provided with these elements how would you prepare 

 a sample of pure chalk ? 



139. A stream of carbonic acid gas is passed through lime-water ; what 

 is the first effect observed, and what is the effect of the continued action of 

 the gas ? How do you account for these different effects ? 



140. Water is carefully added to weighed specimens of quicklime and 

 chalk ; what will be observed ? The residues are now quickly dried at 

 100 C. and weighed again ; account for any differences which may be 

 observed. 



141. Dilute nitric acid is (a) poured into each of three porcelain dishes, 

 the first containing calcium, the second lime, and the third chalk. The 

 contents are then (6) evaporated to dryness and (c) strongly heated. De- 

 scribe what is observed at each stage, and mention the products formed. 



142. 1*5 grams of a mixture consisting of chalk and lime when treated 

 with excess of hydrochloric acid afforded 200 c.c. of gas at 15 C. and 74 cm. 

 pressure. What is the percentage of chalk in the mixture ? 



(A litre of carbonic acid gas at N.T.P. weighs 1-98 grams.) 



143. You are given washing soda, potassium chlorate, hydrochloric acid 

 and metallic calcium. Describe how with these materials you would make 

 a specimen of chalk. Given that calcium on being heated increases in 

 weight by 40 per cent., calculate what weight of chalk could be made from 

 one gram of calcium. 



GENERAL QUESTIONS. 



144. Sketch the apparatus you would employ, and describe fully how 

 you would determine which of two given metals is capable of liberating 

 the greater volume of hydrogen from an acid. 



145. State exactly how you would proceed to collect the following gases : 

 hydrogen, ammonia, carbon dioxide and hydrochloric acid. 



146. For what purpose are the following substances employed in the 

 laboratory : (a) calcium chloride, (6) litmus, and (c) lime-water ? Give 

 examples of their use. 



147. Mention any three substances whose composition alters when left 

 exposed to the atmosphere at ordinary temperature. Explain the cause 

 of the alteration in each case and the experimental evidence on which your 

 explanation is based. 



148. What are oxides ? Give examples of metallic and non-metallic 

 oxides. What oxides enter into the composition of chalk ? How would 

 you experimentally determine the proportions in which they are present 

 in a sample of chalk ? 



149. Oxygen may be prepared by heating potassium chlorate alone, 

 or by heating a mixture of potassium chlorate and manganese dioxide. 

 Why* is the latter process usually employed ? 



If you were required to ascertain the source of the oxygen prepared by 

 the second process, how would you carry out the investigation ? 



