posted by Jake .
A 0.2861 gram sample of an unknown acid (HX) required 32.63 mL of 0.1045 M NaOH for neutralization to a phenolphthalein endpoint. What is the molar mass of the acid?
moles NaOH = M x L
Moles HX = same (the problem tells you it is HX; therefore, we know the reaction is 1:1 with NaOH).
moles HX = grams/molar mass.
You have moles and grams, solve for molar mass.