Here's our cup. The blue dots are the water molecules, nothing else exists. You want to find them out in grams of HCL to add to create a 90,000 parts per million solution. 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.