# What is the molecular weight of acetic acid if a solution that contains 30.0 grams of acetic acid per kilogram of water freezes at -0.93°C. Do these results agree with the assumption that acetic acid has the formula CH3CO2H?

##### 1 Answer

The molecular mass from this experiment is 60 u. This agrees with the value of 60.05 u calculated from the formula CH₃CO₂H.

**1.** Calculate the molality of the solution.

Assume that

**2.** Calculate the molar mass.

Molar mass =

So the molecular mass is 60 u.

You can do the above calculation in one step by rearranging the equation to read

Molar mass =

**3.** Compare with the known value.

The molecular mass of CH₃COOH is 60.05 u.

The experimental and the theoretical values agree within experimental uncertainty.

Here's a video on calculating the molar mass from freezing point depression.