Chemistry - Concentration Terms Question with Solution | TestHub

5 ml of 1.2 M NaOH

$$MolesofNaOH=1.2\times \frac{5}{1000}=\frac{6}{1000}=6\times 10^{-3}moles$$

Now, for a $2\%\left(\frac{W}{V}\right)$ solution of NaOH, there are 2g of NaOH in 100 ml of solution.

$$Moles=\frac{2}{40}$$

$$\frac{2}{40}moles\to 100ml$$

$$1mole\to \frac{100}{2/40}ml$$

$$6\times 10^{-3}moles\to 100\times \frac{40}{2}\times 6\times 10^{-3}ml$$

$$=2000\times 6\times 10^{-3}=12ml$$

So, the water added is $12-5=7ml$.