Sodium carbonate is used to standardize acids in the same way it may be a reagent that you have used KHP in this experiment. In such standardization it was found that a 0.512-g sample of sodium carbonate needed 25.3ml of a sulphuric acid solution to reach the end point for the reaction.
Na2CO3+H2SO------>H2O+CO2+Na2SO4
Find out the molarity of the sodium carbonate?