Question

An aqueous solution is 15.0% by mass of copper(II) sulfate pentahydrate, CuSO4∙5H2O.What

is the molarity of CuSO4 in this solution at 20°C?The density of this solution at 20°C is1.167

g/mL(molecular weight of CuSO4∙5H2O = 249.5, molecular weight of CuSO4 = 159.5)​

Answer 1

0.702 mol / dm³.

Step-by-step explanation

Consider a 1,000 mL sample of this solution. Mass of the sample:

`m = \rho \cdot V = 1.167 \;\text{g}\cdot\text{mL}^(-1)*1,000\;\text{mL} = 1,167\;\text{g}`.

The mass ratio of copper(II) sulfate pentahydrate in this sample is 15 %. In other words,
`1,167 * 15\;\% = 175.1\;\text{g}` among that 1,167 grams of the solution is
`\text{Cu}\text{SO}_4\cdot(\text{H}_2\text{O})_5`.

Number of moles of
`\text{Cu}\text{SO}_4\cdot(\text{H}_2\text{O})_5` in that
`175.1\;\text{g}` of the hydrate:

`n(\text{hydrate}) = \frac{m(\text{hydrate})}{M(\text{hydrate})} = (175.1)/(249.5) = 0.702\;\text{mol}`.

Concentration of the hydrate:

`c(\text{hydrate}) = \frac{n(\text{hydrate})}{V} = \frac{0.702\;\text{mol}}{1,000\;\text{mL}}=\frac{0.702\;\text{mol}}{1\;\text{L}} = 0.702\;\text{mol}\cdot\text{dm}^(-3)`.