 We're starting with 45 grams of hydrogen and we want to know for how many moles of HCl? So you can tackle this as a conversion question. So 45.0 gram H2 and I want to convert into more HCl. Now if I had my hydrogen given in moles then I could read my conversion out of the equation here because I know for each mole there's one here of hydrogen and it's going to be two moles of hydrochloric acid. So I know one mole H2 is two moles of hydrochloric acid. So if you think about this in my conversion, this will kind of be my last step. I want to go from mole H2 to mole HCl so I have two here and one here and then I will end up in mole hydrochloric acid. But now there's one step missing which is I need to go first into mole H2. One mole H2 is how many grams H2. H2 has two hydrogen so one more H2 is two hydrogen. Then we go into purely table and we look at the mass of hydrogen. So the atomic mass of hydrogen is 1 C08 and 1.008 grams H2. So if you calculate this working by the here 2 times C08 sometimes being a bit lazy can hang off because look at this two here that cancels each other out. The one cancels out and the mini cancels out and what I get is that I can calculate my answers as 45 grams divided by 1.008. So 45 grams divided by 1.008. So 8 is 44.6. Three significant figures. I start with 3 grams of HCl and wait not grams. Mole right? I end up in mole. So 45 the grams cancels out, 45 divided by 1.008 is 40.6. Mole HCl.