CHM 213 PAST QUESTION BY EDITION

Question: A is a solution of hydrochloric acid containing 3.650g of HCl in 1dm3 of solution. B is a solution of impure sodium carbonate. 25cm3 of B require 22.7cm3 of A for complete reaction. Given that 5.00g of impure B was dissolved in1dm3 solution,what is the percentage by mass pf pure sodium carbonate in the impure sample

(Na=23, C=12, O=16, Cl=35.5, H=1.00) option : 40.2% option : 78.6% answer : 80.2% option : 60.2%