Final answer:
The percent by mass of the solution made from 15 g NaCl and 66 g water is 18.52%.
Step-by-step explanation:
To calculate the percent by mass of the solution, we need to determine the mass of the solute (NaCl) and the mass of the solution (NaCl + water).
Given that the mass of NaCl is 15 g and the mass of water is 66 g, the total mass of the solution is 15 g + 66 g = 81 g.
To calculate the percent by mass, we divide the mass of the solute by the mass of the solution and multiply by 100.
Percent by mass = (Mass of NaCl / Mass of Solution) x 100%
Substituting the values, we get:
(15 g / 81 g) x 100% = 18.52%