Preparing a Solution

To make a solution, work backwards from the recipe: $200\ \mathrm{mL}$ of $0.5\ \mathrm{M}$ NaCl. First the moles: $n = c \times V = 0.1\ \mathrm{mol}$.

Then the mass, with the molar mass $58.5\ \mathrm{g/mol}$: $m = n \times M = 5.85\ \mathrm{g}$.

Weigh 5.85 g of NaCl for 200 mL of 0.5 M

Dissolve the solid in a little water, then add water up to the $200\ \mathrm{mL}$ mark. V is the volume of the finished solution, not of the water.