The mole
Tutorial 5
Molar mass
Reminder
One mole of atoms are $ 6.023 \cdot 10^{23} $ atoms
One mole of molecules are $ 6.023 \cdot 10^{23} $ molecules
The atomic (molar) mass of an element:
The atomic (molar) mass of an element ($ M $) is the mass (in grams) of one mole of atoms of this element!
The atomic (molar) masses are found in the → periodic table
Molar mass of a substance:
The molar mass of a substance ($ M $) is the mass (in grams) of one mole of molecules or structural units of that substance!
The molar masses of substances are calculated by summing the atomic masses of the → periodic table .
Relationship between mass ($ m $ in g), molar mass $ M $ and number of moles $ n $
$ n $ $ = $ $ \frac{m}{M} $
Calculate the mass of $ 3 $ methane molecules $CH_4$.
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Complete please this question before moving on to the next one!
$M_{CH_4}$ $=$ $12.0+4\cdot 1.0$ $ =$ $ 16.0\;g$
Mass of 1 molecule of methane=
$m_{1\;molecule}$ $ = $ $\frac{M_{CH_4}}{6.0\cdot 10^{23}} = $ $\frac{16.0}{6.0\cdot 10^{23}}\; g$
Mass of 3 molecules of methane=
$m_{3\;molecules} = 3\cdot \frac{16.0}{6.0\cdot 10^{23}}= 8.0\cdot 10^{-23}\;g$
