Question

How much water should be mixed with 12 mL of alcohol so as to obtain 12% alcohol solution ?

Answer 1

Volume of solute = 12 ml
Volume of solution = volume of solute + volume of solvent
Volume of solvent = volume of solution – volume of solvent
= 100 – 12 = 88 ml

$$\begin{gathered} \mathrm{concentration}=\frac{\mathrm{Volume}\mathrm{of}\mathrm{solute}}{\mathrm{volume}\mathrm{of}\mathrm{solute}+\mathrm{volume}\mathrm{of}\mathrm{solvent}}\times 100 \\ 12=\frac{12}{12+x}\times 100 \\ x=88 \end{gathered}$$

So, 88 ml of water will be added to 12 ml of alcohol in order to prepare a concentration 12%.