112 



JUNIOR GRADE SCIENCE 



77. Explain what is meant by the terms efflorescence, decrepitation, 

 sublimation. Give examples of substances which exhibit these phenomena. 

 For what purposes are the following processes employed : evaporation, 

 distillation, filtration, crystallisation ? Give examples of experiments illus- 

 trating the use of each process. 



78. State which of the following substances are (a) crystalline and con- 

 taining water of crystallisation, (6) crystalline without water of crystalli- 

 sation, (c) amorphous, (d) soluble in water, (e) insoluble in water : green 

 vitriol, red lead, nitre, sulphur, salt, chalk, washing soda, caustic potash, 

 lime and magnesium oxide. 



79. How would you obtain pure specimens of sand, salt and sal-ammoniac 

 from a mixture of these three substances ? 



80. Describe briefly how you would investigate completely the nature of 

 sublimation, with the aid of a suitable substance. 



81. Give a short account of what you have learnt on the subject of crystal- 

 lisation. 



82. You are required to draw a curve to show the effect of change of 

 temperature on the solubility of a given substance ; state in detail your 

 method of obtaining it. 



83. How would you ascertain whether a given solution were saturated ? 

 Describe how you would determine the amount of water required to dissolve 

 100 grams of nitre at 20 C. 



84. On evaporating 25 grams of a clear saturated aqueous solution at 

 15 C., 1-85 grams of residue are obtained. In what terms would you 

 express the solubility of the substance in water ? 



85. The following table gives the weights of residues obtained by evapor- 

 ating given quantities of nitre solution saturated at the temperatures 

 indicated : 



Draw a graph showing the solubility of nitre, and from it determine the 

 least quantity of water required to dissolve 100 grams of nitre at 57 C. 



86. What is a saturated solution ? What effect has change of tempera- 

 ture on such a solution of aluni ? Has the rapidity with which such a 

 change takes place any effect upon the result ? 



