EFFECT OF TEMPERATURE 63 



(3) When both the constituents are weak the solution will 

 remain neutral, if acid and base are of equal strength, if the acid 

 be the stronger, the solution will be acid, and conversely an 

 alkaline solution will be produced if the base be stronger than 

 the acid. E.g. 



CH 3 COONH 4 + H 2 O NH 4 OH + CH 3 COOH. 



This solution will be almost neutral, because the degrees of 

 ionisation of ammonium hydrate and acetic acid are almost 

 identical. 



Effect of Temperature. 



The effect of temperature on the dissociation of water has been 

 dealt with above (p. 56 and Table VIII.). Increase in temperature 

 causes a very large increase in the amount of water ionised. An 

 increase in temperature of 1C, say from 38 to 39, causes the 

 [H] x[OH] to rise from 10~ 13 - 5 to 10~ 13 ' 47 , an increase of about 

 20 per cent. Strong electrolytes have a low temperature coeffi- 

 cient of dissociation. It is, therefore, obvious that increase of 

 temperature will affect salts according to the dissociation constant 

 of the acids and bases composing them. 



(a) Both strong, temperature of little effect. 



(b) Weak acid -f strong base. Increase of temperature causes 

 the degree of dissociation of acid to increase. Acid ions combine 

 with hydrogen ions from H 2 O and liberate OH~. 



(c) Strong acid and weak base. Increase of temperature 

 causes the degree of dissociation of base to increase. Base ions 

 combine with hydroxyl ions from the H 2 O and liberate H f . 



(d) Both weak. The result of any increase in temperature is 

 to increase the dissociation of the weaker at a greater rate than 

 the stronger with correspondingly slight changes in [H] and [OH]. 



It will be seen that apart from the action of temperature on 

 the dissociation of water itself, in (b) increased alkalinity and in 

 (c) increased acidity result from increase in temperature. This 

 action is slight, however, compared to the action of temperature 

 on the weakest salt known, water. 



The effect of alterations of temperature on a salt solution where 

 one of the constituents of the salt is weak is the combined effect of 



I. the alteration in K H2O ; 

 II. the alteration in K SaJt . 



In brief, the increased acidity or alkalinity produced by increase 

 of temperature is greater (theoretically) than could have been 



