Question

how much water should be added to 500g of salt to obtain 2.5% of salt solution?

Answer 1

Given :
Mass of solute (salt ) = 500 g
Mass percentage = 2.5 %

Mass percentage = $\frac{\mathrm{Mass}\mathrm{of}\mathrm{solute}}{\mathrm{Mass}\mathrm{of}\mathrm{solution}}\times 100$
Substituting the values

$$\begin{gathered} 2.5=\frac{500}{\mathrm{Mass}\mathrm{of}\mathrm{solution}}\times 100 \\ \Rightarrow \mathrm{Mass}\mathrm{of}\mathrm{solution}=\frac{500}{2.5}\times 100 \\ =20000\mathrm{g} \\ =20\mathrm{kg} \end{gathered}$$
Mass of solution = 20000 g
Mass of solute = 500 g
Mass of solvent (water) = 20000 - 500 = 19500 g

Thus 19500 g water should be added to 500 g salt to make 2.5 % solution.