A solution containing 1.22 g of a diprotic acid H2CH2O4 (malonic acid) was titrated with 45.5 mL of NaOH to reach the second equivalence
point. What is the concentration of the NaOH solution? (MW_malonic
acid = 104.06 g/mol)

0.515 M

Explanation:

The reaction that takes place is:

First we convert 1.22 g of malonic acid into moles, using its molar mass:

Then we convert 0.01172 malonic acid moles into NaOH moles, using the stoichiometric coefficients of the balanced reaction:

Finally we calculate the concentration of the NaOH solution, using the number of moles and given volume:

Converting 45.5 mL ⇒ 45.5/1000 = 0.0455 L