# Question 7b377

Nov 23, 2017

Make it clear what kind of concentration you are going to calculate.

#### Explanation:

There are variety of concentration. First, you must be clear what kind of concentration you want to find.
https://en.wikipedia.org/wiki/Concentration

If you want to calculate mass concentration, divide the mass of the solute $m$ by the volume of solution $V$.

ρ=m/V

Dissolving $60$ g $N a O H$ in $100$ ml water, the volume of the solution will be so different from $100$ ml.

Instead, you can calculate mass fraction.
$100$ ml of water is $100$ g and the mass of solution is $60 + 100 = 160$ g.
Mass fraction of $N a O H$ in this solution is $w = \text{mass of solute"/"mass of solution} = \frac{60}{160} = 0.375$, or 37.5%#.

[Some evaluation]
Acording to CRC databook, the density of $N a O H$ solution with mass fraction $0.360$ and $0.380$ is $1.3900$ and $1.4101$ respectively. (g/ml) Data are cited from http://www.edu.utsunomiya-u.ac.jp/chem/v8n1/ashida1/TabC05.htm.

Density of this $N a O H$ solution ($w = 0.375$) will be about $1.4051$(linear interpolation is applied).

The volume of the solution is about $\frac{160 g}{1.4051 \frac{g}{m L}} = 113.87$ (mL) and
the mass concentration is about $\frac{60 \left(g\right)}{0.11387 \left(L\right)} = 526.91$ (g/L).