This is about back titration to determine the percentage of sodium carbonate in an unknown sample by reaction with excess sulfuric acid followed by the back titration of the acid with sodium hydroxide

Information:

H2SO4
M=0.05137

Mass of impure sample of Na2CO3
m=1.5033g

Part A.

Standardization of NaOH solution: 24.27ml NaOH
25ml of H2SO4

Part B.

the impure carbonate is dissolved in 250ml of deionized water
each flask has:
50 ml H2SO4
25ml of impure solution
that has been back titrated with 38.15ml NaOH

Questions:

1)How do you calculate the moles of sulfuric acid that remained in the solution after the reaction with the carbonate?

2) calculate the moles of sulfuric acid that reacted with the carbonate

3) calculate the moles of sodium carbonate present in the original 25.00ml and 250.0ml of solution.

4) calculate the percent of sodium carbonate in the impure sample.