acid base tritation. is it citric acid or tartaric acid?

Question

an unknown solid acid is either citric acid or tartaric acid. to determine which acid you have, you need to titrate a sample of the solid with NaOH. The appropriate reactions are:

citric acid
H3C6H5O7 + 3NaOH --> Na3C6H5O7 +3H2O

tartaric acid
H2C4H4O6 +2NaOH --> Na2C4H4O6 + 2H2O

you find that a .956 g sample requires 29.1 ml of .513 M NaOH for titration to the equivalence point. What is the unknown acid?

I got citric acid. but i'm not sure. could you show me how you go to the answer...because i figured out the moles then i did some stoichiometry and then i don't know exactly what i did...but i got citric acid. please help!!


thank you.

Answer 1

The molar mass of citric acid (C6H8O7) = 192 g/mol
The molar mass of tartaric acid (C4H6O6) = 150 g/mol

If the sample is citric acid; 0.956 g / 192 g/mol = 0.005 mol
If the sample is tartaric acid; 0.956 g / 150 g/mol = 0.006 mol

The mole of NaOH required for titration;
n = M x V = (0.513 mol/L) x (0.0291 L) = 0.015 mol

According to the equations; For each mole of citric acid 3 moles of NaOH is required, for 0.05 mol citric acid 0.05x3= 0.015 mol NaOH is required. (Gives the exact value)
According to the equations; For each mole of tartaric acid 2 moles of NaOH is required, for 0.06 mol citric acid 0.06x2= 0.012 mol NaOH is required. (It is less than the amount consumed)
Therefore your sample is citric acid.

Answer 2

Tartaric Acid Molar Mass

Answer 3

That looks like the way you do it. You find the moles in your NaOH solution and find out which acid has the number of moles (based on the reaction) for 0.956 grams.