25.0cm³ portions of 0.100mol in 1000cm³ solution of sodium trioxocarbonate(iv) were titrated against hydrochloric acid solution

Would you please tell me the source of your name for Na2CO3. That is NOT a correct name and IUPAC does not accept it as a correct name. Is the source a teacher, text, the web. We need to stamp out this odd-ball naming. I don't see a question. I see only a statement. If you want to know the molarity of the HCl solution we must know how much HCl was used.