Question

Question #7b377

Answer 1

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`

Your answer is wrong because you used the volume of solvent instead of solution.
Dissolving `60` g `NaOH` 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 `NaOH` in this solution is `w="mass of solute"/"mass of solution"=60/160=0.375`, or `37.5%`.

[Some evaluation]
Acording to CRC databook, the density of `NaOH` 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 `NaOH` solution (`w=0.375`) will be about `1.4051`(linear interpolation is applied).

The volume of the solution is about `(160 g)/(1.4051 g/(mL))=113.87` (mL) and
the mass concentration is about `(60(g))/(0.11387(L))=526.91` (g/L).