# Question #36be0

##### 1 Answer

#### Explanation:

The formula for molality

#color(blue)(bar(ul(|color(white)(a/a)b = "moles of solute"/"kilograms of solvent" color(white)(a/a)|)))" "#

It will be more convenient during the derivation to express the mass of solvent in grams rather than kilograms.

Then,

where

Since

we can write

**(1)**

where

The formula for mass percent is

#color(blue)(bar(ul(|color(white)(a/a)"Mass %" = "mass"/"total mass" × 100 %color(white)(a/a)|)))" "#

or

**(2)**

where

From (1),

**(3)**

Substitute (3) into (2)

Multiply numerator and denominator by

#color(blue)(bar(ul(|color(white)(a/a)"Mass %" = b/(b + 1000/M) × 100 %color(white)(a/a)|)))" "#

**Example**

Calculate the mass percent of a 1.00 mol/kg solution of