How can I find the molecular weight of an organic acid?

My question is in regard to finding the molecular weight of an unknown organic acid. What would be the best way to go about doing it? I thought maybe by using a titration. Unfortunately, I am stuck at this point as what to do next. christopher (jodiniz@zeus.kern.org)

A titration would work if you know how many ionizable hydrogens your organic acid has, and if you knew how pure the sample was. The following procedure could be used to get an estimate of the acid's molecular weight:

Weigh the acid sample. If you know the purity, figure out how many grams of acid you actually have.
Titrate the acid with a strong base solution of precisely known concentration (say, 0.1000 M KOH).
Calculate how many moles of KOH were added.
Convert moles of KOH to moles of acid.
Divide the mass of acid you titrated by moles of acid and you have your molar mass.

That's probably the simplest way to do it. There are many other ways. For example, if the acid is volatile, you can try the Dumas method (The molecular weight is g/n which is approximately dRT/P, where d, P, and T are the experimentally measured density, pressure, and temperature of a vaporized acid sample at low pressure).

Author: Fred Senese senese@antoine.frostburg.edu

General Chemistry Online! How can I find the molecular weight of an organic acid?