**At equivalence point:**

**moles acid = moles base**

$\mathbf{mole}\mathbf{}\mathbf{acid}\mathbf{}\mathbf{=}\mathbf{}\mathbf{mole}\mathbf{}\mathbf{base}\mathbf{}\mathbf{=}\mathbf{25}\mathbf{}\overline{)\mathbf{mL}\mathbf{}\mathbf{NaOH}}\left(\frac{{10}^{-3}\overline{)L}}{1\overline{)\mathrm{mL}}}\right)\left(\frac{0.500\mathrm{mol}\mathrm{NaOH}}{1\overline{)L\mathrm{NaOH}}}\right)\mathbf{=}$**0.0125 mol**

Determine the molar mass:

${\mathbf{MM}}_{\mathbf{acid}}\mathbf{=}\frac{\mathbf{2}\mathbf{.}\mathbf{20}\mathbf{}\mathbf{g}\mathbf{}\mathbf{acid}}{\mathbf{0}\mathbf{.}\mathbf{0125}\mathbf{}\mathbf{mol}\mathbf{}\mathbf{acid}}\mathbf{=}$**176 g/mol**

The empirical formula weight of the unknown acid is 88.062 g/mol.

A 2.20-g sample of an unknown acid (empirical formula = C _{3}H_{4}O_{3}) is dissolved in 1.0 L of water. A titration required 25.0 mL of 0.500 M NaOH to react completely with all the acid present. Assuming the unknown acid has one acidic proton per molecule, what is the molecular formula of the unknown acid?

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