The ache, or \"burn\" you feel in your muscles during strenuous exercise is caus

Question

The ache, or "burn" you feel in your muscles during strenuous exercise is caused by the accumulation of lactic acid, which has the structure shown below. The hydrogen atom in the COOH group is acidic and it can be removed using base to form a COO^- group. To determine the concentration of a solution of lactic acid, a chemist titrates a 21.00 mL sample of it with 0.1010 M NaOH, and finds that 15.82 mL of titrant are required to reach the equivalence point. What is the concentration of the lactic acid solution in moles per liter?

Explanation / Answer

Lactic acid is a monoprotic acid. SO, it reacts 1:1 molar ratio with NaOH
Mol NaOH in 15.82 mL of 0.1010M NaOH = (15.82/1000 L)*(0.1010 M) = 1.598 *10^-3 mol NaOH

Therefore the 21mL of lactic acid solution contains 1.598 *10^-3 acid
Mol acid in 1000mL = (1000/21)*(1.598 *10^-3) = 0.076 mol in 1000mL solution

Molarity of lactic acid solution = 0.076 M

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