Question

if 40.0 grams of ammonium hydroxide are added to 200mL of water, what is the percent by mass of this solution?

Answer 1

1 mL of water weighs exactly 1 gram. 200 ml of water is therefore 200 grams. If we add  40.0 grams of ammonium hydroxide, the total weight of the solution is 240 grams, and the percentage of the salt is 40/200 * 100 = 20%