Question

An unknown solid acid is either citric acid or tartaric acid. To determine which acid you have, you titrate a sample of the solid with NaOH. The appropriate reactions are as follows:
Citric acid:
H3C6H5O7 (aq) + 3NaOH (aq) -> 3H2O (l) + Na3C6H5O7 (aq)

Tartaric acid:
H2C4H4O6 (aq) + 2 NaOH (aq) -> 2H2O (l) + Na2C4H4O6

A 0.956g sample requires 29.1 mL of 0.513 M NaOH for titration to the equivalence point. What is the identity of the unknown acid?

Answer 1

mols base = M x L = ?
If citric acid, then mols citric acid = 1/3 mols NaOH.
If tartaric acid, then mols tartaric acid = 1/2 mols NaOH.

mols = grams/molar mass or
molar mass = grams/mols.

If citric acid then molar mass = 0.956/mols citric acid from above.
If tartaric acid then molar mass = 0.956/mols tartaric acid from above.

Look up or calculate the molar mass of both tartaric acid and citric acid and compare with the molar mass of the unknown you calculated.