I have a chem test this week and I’m absolutely stumped on this, I’m terrible at math so any help would be appreciated.
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It’s actually rather simple. “Mole” (M) may be called a unit, but it’s kind of not, it’s just a number. 1 M consists of roughly 6.02214076×10^(23) atoms, no matter what element.
The gram formula mass is a means to describe the mass of an atom or molecule. The unit is gram per mole (g/M), meaning the mass of 1 mole (6.02214076×10^(23) atoms) of the given substance. It is used to determine how much mass of a substance you need to get a complete chemical reaction. The GFM of elements is in the periodic table and you should have access to one during exercises and exams.
As an example: 1 M of Oxygen would completely react with 2 M of Hydrogen to become water, because each molecule of the water consists of 1 Oxygen atom and 2 Hydrogen atoms.
O + 2 H = H2O
The GFM of Hydrogen is ~1 g/M and that of Oxygen is ~16 g/M.
So you need
1 M * 16 g/M = 16 g
of Oxygen and
2 M * 1 g/M = 2 g
of Hydrogen, to have a complete reaction, with no atom being left over.
Now, the GFM of water is the combined GFM of the atoms of the molecule. It’s 2 Hydrogen atoms and 1 Oxygen atom for each water molecule, so
2 * 1 g/M + 1 * 16 g/M = 18 g/M
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