A 19.0-mL sample of tartaric acid is titrated to a phenolphthalein endpoint with 20.mL of 1.0 M NaOH.Assuming tartaric acid is diprotic,what is the molarity of the acid?

Question

Quizplus · Accepted Answer

Since tartaric acid is diprotic, it reacts with 2 moles of NaOH per mole of acid. The balanced chemical equation for the reaction is:

H2C4H4O6 + 2NaOH → Na2C4H4O6 + 2H2O

From the balanced equation, we can see that the moles of NaOH used in the titration is equal to twice the moles of tartaric acid in the sample. Therefore,

moles of tartaric acid = 0.5 * 1.0 M * 20.0 mL / 1000 mL = 0.01 mol

So the molarity of the acid is:

Molarity = moles of acid / volume of acid = 0.01 mol / 19.0 mL x (1 L / 1000 mL) = 0.526 M, which rounds to 0.53 M. Therefore, the best choice is B.

A 190-ML Sample of Tartaric Acid Is Titrated to a Phenolphthalein