The mole
Tutorial 7
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 atomic mass of the cadmium, knowing that by decomposition of $ 0.764 \; g $ of $ CdCl_2 $ one gets $ 0.468 \; g $ of pure cadmium $ Cd $ and chlorine.
Go through the number of moles of chlorine!
For answers, use (possibly several times) the arrows ↑ Down! and ↓ Up!
Complete please this question before moving on to the next one!
$m_{Cl}$ $=$ $0.764-0.468$ $=$ $0.296\;g$
Number of moles of chlorine atoms=
$\frac{0.296}{35.5}\;mol$
Number of moles of cadmium atoms =
$\frac{0.296}{2\cdot 35.5}\;mol$
Each molecule contains two atoms of chlorine and only one of cadmium!
Atomic (molar) mass of $Cd$=
$M$ $=$ $\frac{m}{n}$ $=$ $\frac{0.468}{\frac{0.296}{2\cdot 35.5}}$ $ = $ $112\frac{g}{mol}$
