We’re being asked to calculate the mass of NaCl needed to prepare 0.250 L of 0.800 M NaCl solution. To do this, we will use the formula for molarity. Recall that molarity is the ratio of the moles of solute and the volume of solution (in liters). In other words:
We first need to determine the number of moles of NaCl from molarity and volume
Given: Molarity (mol/L) = 0.800 mol/L
Volume = 0.250 L
Let's say we want to make 0.250 L of an aqueous solution with [NaCl] = 0.800 M. What mass of the solute, NaCl, would we need to make this solution?