Concentrated hydrochloric acid is a solution that is 37.5% mass per unit volume HCl(aq) in water. An old bottle of HCl has an unknown concentration. What is the concentration of hydrochloric acid, [HCl], in the old bottle, if 9.95 mL of 12.0 M NaOH(aq) is required to reach the equivalence point when added to 15 mL of acid?What is the concentration of HCl(aq)?

Explanation:

Hello,

In this case, since the neutralization reaction between HCl and NaOH is:

We notice a 1:1 molar ratio, for that reason, at the equivalence point we find:

Thus in terms in molarities one could compute the concentration of HCl in the old bottle for the used NaOH for the neutralization as:

This value is lower than 37% HCl that in molarity is about 12 M, such difference is due to its high volatility.

Best regards.

the formula mass of a molecule or a compound is the sum of the atomic weights of the atoms in its empirical formula

(that's what i know about formula mass)