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## Do you include the coefficient for molar mass?

- Students get a little confused sometimes whether or not to include the coefficient when determining
**Molar Mass**. - Molar mass means the mass of
**1 mole of substance** - You just have to multiply the atomic mass of each individual atom by the subscripts and add them up
**The molar mass of water is always (2 x H) + (1 x O) = 18g/mol**- However, if you want to know what the mass of 6 moles of water is, then the total mass is (6mol x 18g/mol) = 108g.

## Do you include the coefficient of water molecules in hydrates?

- Should you include the coefficient of water molecules

when you calculate the molar mass of a hydrate such as Magnesium sulfate heptahydrate? - The answer is YES!
- Even though there are 7 molecules of water,

the water is incorporated into ONE MOLE of the

solid ionic compound. - Mg=24.305

S=32.06

O=16.0

H=1.0

Multiply each atomic weight by the total no of each atom:

MgSO4.7H2O –> 1 Mg, 1 S, 11 O, 14 H - Molar mass = (1 x 24.305) + (1 x 32.06) + (11 x 16) + (14 x 1)
- The molar mass of magnesium sulfate heptahydrate is
**246.365 g/mol**