Question

Assuming ideal behavior, what is the boiling point for a solution that contains 35.7 g NaCl (58.44 g/mol) and 100.0 g H2O?

Tf, pure water = 0.00 Celsius
Tb, pure water = 100 Celsius
Kf = -1.86 C kg/ mol
Kb = 0.512 C kg/ mol

Answer 1

Given,

`K_"b" = (0.512°"C" * "kg")/"mol"`

`m = (35.7"g" * "mol"/(58.44"g"))/(0.1000"kg") approx 6.11"m"`

`i = 2` (assuming no ion pairing)

Now, recall,

`DeltaT_"b" = iK_"b"m`

Hence,

`DeltaT_"b" = iK_"b"m approx 6.26°"C"`,

and by extension, the boiling point of the solution will be approximately `106.26°"C"`.