Question

Calculate the number of moles of magnesium present in a magnesium ribbon weighing $12\mathrm{g}$. The molar atomic mass of magnesium is $24\mathrm{g}{\mathrm{mol}}^{-1}$.

Answer 1

Step 1: Analyse the formula to calculate the number of moles.

• The number of moles can be calculated by using the formula:

$\mathrm{Number}\mathrm{of}\mathrm{moles}=\frac{\mathrm{Given}\mathrm{mass}}{\mathrm{Molar}\mathrm{mass}}$

• According to the question, the given mass is $12\mathrm{g}$ and the molecular mass can be calculated.

Step 2: Calculate the molecular mass of helium.

• To find the molecular mass, we will add the atomic masses of all of the atoms in the molecule.
• In this case, there is only one atom of magnesium ($\mathrm{Mg}$) in the molecule magnesium ribbon of ($\mathrm{Mg}$).
• So, the molecular mass of the magnesium ribbon $=24\mathrm{g}{\mathrm{mol}}^{-1}$

Step 3: Calculate the number of moles.

• The given mass is $12\mathrm{g}$ and the molar mass is $24\mathrm{g}{\mathrm{mol}}^{-1}$
• So, the number of moles of $\mathrm{Mg}$ are $\frac{12\mathrm{g}}{24\mathrm{g}{\mathrm{mol}}^{-1}}=0.5\mathrm{moles}$

Hence, the number of moles of magnesium present in $12\mathrm{g}$ of magnesium ribbon is $0.5\mathrm{moles}$.