## Fundamental E

SajaZidan_1K
Posts: 56
Joined: Wed Sep 18, 2019 12:15 am

### Fundamental E

Self Test E.1B states, "A double espresso contains 3.14 mol H2O. What is the number of H atoms present in the espresso?"

Based on the result, I was confused as to why oxygen was not subtracted from the number of H atoms. Anyone know why oxygen is not subtracted from the total number of H atoms present since the mol of H2O is used to solve the problem?

Haley Chun 4H
Posts: 54
Joined: Sat Aug 17, 2019 12:18 am

### Re: Fundamental E

I think you have to use molar ratios for this question because the number of atoms of H and O do not add up to the number of water molecules. There are 2 moles of Hydrogen and 1 mole of O for every 1 mole of H2O, so i think you do:
(3.14 mol H2O) x (2 mol H/1 mol H2O) x (6.022 x 10*23 atoms/1 mol H)

Helen Struble 2F
Posts: 97
Joined: Sat Aug 24, 2019 12:17 am

### Re: Fundamental E

Because you know how many moles of H2O are in the coffee, you can use molar ratios to find the solution. Because it is H2O, we know that there are two hydrogen atoms in each water molecule, therefore for each mole water, there are two moles hydrogen. Then, we can set up a conversion factor: 2 moles hydrogen/1 mole H2O. Using this conversion factor and Avagadro's number, we can find how many hydrogen atoms are in the double espresso.