Question

Estimate the molar mass of Aluminium.

Answer 1

Hint: Consider the position of Aluminium in the periodic table. It is a p-block element. The atomic number of Aluminium is 13.
The molar mass of any compound is defined as the mass in grams when 1 mole of that particular substance is taken. It is usually expressed in \[g/mol\] . 1 mole will contain \[6.022 \times {10^{23}}\] atoms, ions or molecules.

Complete answer:
To calculate the molar mass we have to first know what mass means-
Atomic mass is the sum of the total number of neutrons and protons that are present in the atom. Atomic mass is usually represented in atomic mass units (amu). To convert atomic mass to molar mass we have to multiply the atomic mass in amu by the molar mass constant( 1 \[g/mol\] ).
Atomic mass of aluminium = Number of protons + Number of neutrons
\[ \Rightarrow 13 + 14\]
\[ \Rightarrow 27{\text{ amu}}\]
Therefore the atomic mass of aluminium is 27 amu or 27 \[g/mol\] .

Additional information:
An atomic unit of mass is defined as accurately \[\dfrac{1}{2}th\] the mass of a carbon-12 atom. In SI unit (kg) we can say that 1 amu is equal to \[1.67377{\text{ }} \times {\text{ }}10{\;^{ - 27}}\;kilogram{\text{ }}\left( {kg} \right)\] .
\[ \Rightarrow 1{\text{ }}amu = {\text{ }}\dfrac{{{\text{Mass of }}_6^{12}{\text{C Atom}}}}{{12}}\]
By substituting the value of \[{\text{Mass of }}_6^{12}{\text{C Atom}}\] as \[1.998467052 \times {10^ - }^{26}\;kg\] we can get the value of 1 amu in kg.
\[ \Rightarrow 1{\text{ }}amu = {\text{ }}\dfrac{{1.998467052 \times {{10}^ - }^{26}\;kg}}{{12}}\]
\[ \Rightarrow 1{\text{ }}amu = 1.662{\text{ }} \times {\text{ }}{10^{ - 24}}g{\text{ or }}1.662{\text{ }} \times {\text{ }}{10^{ - 27}}kg\]

Note:
When you are given questions just calculate the atomic mass in atomic mass unit and then multiply it with 1 \[g/mol\]. This will give you the molar mass of the given compound. If you are given a compound for which you have to calculate the molar mass by just adding the atomic masses of all the elements in the compound.
E.g. Molar mass of \[NaCl\] is given as:
\[ \Rightarrow \] Molar mass of \[Na\] + Molar mass of \[Cl\]
\[ \Rightarrow 22.99 + 35.45\]
\[ \Rightarrow 58.44{\text{ }}g/mol\]