Question

A solution of an unknown compound has a concentration of 27.3 % by mass. Howmany moles are present in 0.965 kg of solution if the solute has a molar mass of 25.2g/mol?

Answer 1

1) Mass percent

`\%=\frac{gramsofsolute_{}}{gramsofsolution}\cdot100`

2) List known values

Sample: 0.965 kg

`g=0.965kg\cdot(1000g)/(1kg)=965g`

2) Plug in known values and solve for grams of solute.

`27.3\%=\frac{\text{grams of solute}}{965\text{ g solution}}\cdot100`
`gSolute_{}=27.3\cdot\frac{965\text{ g solution}}{100}_{}=263.445\text{ g solution}`

3) Convert grams of solute to moles

The molar mass of the unknown compound is 25.2 g/mol

`mol_{}=263.445g\cdot\frac{1mol_{}}{25.2g_{}}=10.45mol_{}`

There are 10.45 moles of the unknown compound present in the sample.