Question

A chemistry student weighs out of lactic acid into a volumetric flask and dilutes to the mark with distilled water. He plans to titrate the acid with solution. Calculate the volume of solution the student will need to add to reach the equivalence point. Round your answer to significant digits

Answer 1

28.0mL of the 0.0500M NaOH solution

Step-by-step explanation:

0.126g of lactic acid diluted to 250mL. Titrated with 0.0500M NaOH solution.

The reaction of lactic acid, H₃C-CH(OH)-COOH (Molar mass: 90.08g/mol) with NaOH is:

H₃C-CH(OH)-COOH + NaOH → H₃C-CH(OH)-COO⁻ + Na⁺ + H₂O

Where 1 mole of the acid reacts per mole of the base.

You must know the student will reach equivalence point when moles of lactic acid = moles NaOH.

the student will titrate the 0.126g of H₃C-CH(OH)-COOH. In moles (Using molar mass) are:

0.126g ₓ (1mol / 90.08g) = 1.40x10⁻³ moles of H₃C-CH(OH)-COOH

To reach equivalence point, the student must add 1.40x10⁻³ moles of NaOH. These moles comes from:

1.40x10⁻³ moles of NaOH ₓ (1L / 0.0500moles NaOH) = 0.0280L of the 0.0500M NaOH =

28.0mL of the 0.0500M NaOH solution