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 add, a chemist titrates a 21.75 mL sample of it with 0.1010 M NaOH, and finds that 10.43 mL of titrant are required to reach the equivalence point. What is the concentration of the lactic add solution in moles per liter?

Answer 1

Step 1

Calculate moles of NaOH

Moles of NaOH = Volume in L x molarity

0.01043 L x 0.1010 M =   0.01043*0.1010=0.00105 mol NaOH

Mol ratio between lactic acid and NaOH is 1:1

Therefore, moles of lactic acid = moles of NaOH

Now calculate molarity

Molarity of lactic acid = 0.00105 mol lactic acid / volume in L

0.00105/0.02175=0.04828 M

Molarity of lactic acid = 0.050 M