Hello all,

I am having a trouble with a specific question from a lab assignment regarding aspirin.

A 0.331g sample of aspirin prepared in the laboratory was dissolved in 95% ethanol and titrated to a phenolphthalein endpoint with 16.7ml of 0.107M of NaOH.

a. Calculate the moles of acetylsalicylic acid in the aspirin sample.
b. What mass (g) of acetylsalicylic acid is present in the aspirin sample?
c. Calculate the percent purity of the aspirin sample.

1)Formula of aspirin is C9H8O4
Calculate its molar mass
C9H8O4 + NaOH ----> C9H8O4-Na+ + H2O
now one mole of NaOH reacts with one mole of aspirin
get the moles of NaOH
moles of NaOH = Molarity *volume in L =0.107M*16.7ml  *1L/1000mL

Now
moles of aspirin = moles of NaOH
grams of aspirin in the sample = moles of aspirin *Molar mass of the substance
now you can work out the percent as the mass of (aspirin / mass of sample )   X 100%