100 cm^3 of 0.05M sulphuric (VI) acid were placed in a flask and a small quantity of anhydrous sodium carbonate added. The mixture was boiled to expel all the carbon (IV) oxide. 25cm^3 of the resulting solution required 18 cm^3 of 0.1 M sodium hydroxide solution to neutralize it. Calculate the mass of sodium carbonate added. (Na =23.0; O = 16.0 ;C= 12.0) (KCSE 2014 paper 1 question 13.)