DISSOCIATION OF SALTS 



69 



Na.,CO.. 



CO3- 



HCO3 



HoCO. 



HoO 



2Na ■ 

 H' 



+ CO, 



HoO = H2CO3 

 =zHoO 



+ OH- 

 + OH- 

 OH 



+ COo 



If the CO2 is allowed to escape, the last reaction will only cease 

 when all the H2CO3 has been decomposed. The total resnlt is 

 an increase in [OH] and, therefore, of alkalinity. 



{b) In the case of a weak base combined with a strong acid, 

 the solutions become acid, as the following equations denote. 



BA = 



= BOH + H 



HoO = 



where HA is a strong acid and BOH a weak base. 



E.g. 



NHXl 



HoO 



= NH4OH 



H^ +C1 



(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. 



CH3COONH4 + H2O = NH4OH + CH3COOH. 



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. 62 and Table VIII.). Increase in temperature 

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

 increase in temperature of 1° C, say from 37° to 38°, causes the 

 [H] X [OH] to rise from 10"^^^ to 10"^^*^ an increase of about 

 10 per cent. Strong electrolytes have a low^ temperature coeffi- 

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



