So you want to go from this cup to this cup, where this cup contains HCL molecules in the concentration of 90,000 parts per million. We want to find the amount of grams of the red dots we need to add to create such a solution. The first step is to calculate the molecular weight of water. To calculate the molecular weight of water, we simply add the atomic weight of oxygen plus two times the atomic weight of H because we have a substrate of two, so we get 16 grams/mol of oxygen plus two times 1 gram/mol of H gives us 18 grams/mol. So the molecular weight of water is 18 grams/mol. Now, to find the amount in grams of water that we have in our initial solution, we need to multiply the molecular weight by the 25 moles of H 20 that we have.