Question

What is the freezing point of a 50% by volume ethanol solution? Assume water is the solvent. (Use data from Table 12.7 in textbook -for your reference, the text is ‘Chemistry a Molecular Approach’ by Tro et al).

Answer 1

Recall,

`DeltaT_f = iK_fm`

`50%` by volume ethanol solution is equal to (assuming `100"mL"`),

`50"mL" * (1.0"g")/("mL") * "kg"/(10^3"g") approx 5.0*10^-2"kg"` of water, and,

`50"mL" * (0.789"g")/("mL") * "mol"/(46.07"g") approx 0.856"mol"` of ethanol.

Hence,

`DeltaT_f = 1 * (1.86°C)/m * (0.856"mol")/(5.0*10^-2"kg")`

`therefore T_f = 31.9°C`,

and by extension `-31.9°C` is the freezing point of that particular solution.

Note, I don't have your text, so I used data from literature. If you see something in my work that is inconsistent with your text, just re-run the calculations.