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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**

## 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**

Thank you very much i knew that when we calculate molar mass we do multiply by the cofficient

NO! You

do notinclude coefficient in your molar mass. In hydrates, coefficients in front of the water molecule is used.But it says in the beginning “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.” So do you use the coefficient or not???

Statement removed since it causes confusion.

Molar mass refers to mass of 1 mole of that substance and 1 mole only.