So we have the number of grams we need to add. But our question asks us to find the number of moles. To find that, we need to find the molecular weight of sodium chloride. To find the molecular weight of sodium chloride, we simply add the atomic weights of sodium and chloride. So 23 grams/mol plus 35.5
grams/mol gives us 58.5 grams/mol. This is a molecular weight of sodium chloride.