Question

1. Aspirin is a monoprotic acid. Calculate the volume of 0.493 M NaOH required to titrate a 0.1527-g sample of aspirin. (Pay attention to significant figures in your answer.)

2. A student reached the end point of the titration in the previous question 0.34 mL before expected based on the volume calculated in question 1. What is the purity of the sample?

3. A student required more titrant than predicted as necessary in question 1. Explain why this might occur.

Answer 1

1. First calculate number of moles of aspirin present in 0.1527 g of given sample of aspirin.

Molecular mass of aspirin = 180.157 g/mol

No. of moles = mass of sample / molecular mass = 0.1527/180.157 = 8.40 x 10^-4 moles

Since aspirin is monoprotic acid,

Number of aspirin = Number of moles of NaOH = 8.40 x 10^-4 moles

Molarity = No. of moles / Volume of solution (in L)

Volume of Solution (NaOH) = 8.40 x 10^-4 / 0.493 = 1.7 x 10^-3 L = 1.72 ml

Therefore 1.72 ml of 0.493 M NaOH solution is required to titrate given sample of aspirin.