Question

Calculate the mass of oxygen which contains same number of atoms as are present in 4.6g of sodium.

Answer 1

Step 1:

Calculating the moles of sodium:

The atomic mass of sodium = $23{\mathrm{gmol}}^{-1}$

Given the mass of sodium = 4.6g

$$\begin{gathered} \mathrm{Number}\mathrm{of}\mathrm{moles}=\frac{\mathrm{Given}\mathrm{mass}\mathrm{of}\mathrm{substance}}{\mathrm{Atomic}\mathrm{mass}\mathrm{of}\mathrm{atom}} \\ \mathrm{Number}\mathrm{of}\mathrm{moles}\mathrm{of}\mathrm{sodium}=\frac{4.6}{23}=0.2\mathrm{moles} \end{gathered}$$

Hence, the number of moles of sodium is 0.2 moles

Step 2:

Calculating the mass of oxygen:

Since the number of atoms of oxygen and sodium is the same, therefore, the number of moles also will be the same.

Number of moles of oxygen = 0.2 mole

The atomic mass of oxygen = $16{\mathrm{gmol}}^{-1}$

$\begin{array}{rcl}\mathrm{Number}\mathrm{of}\mathrm{moles}& =& \frac{\mathrm{Given}\mathrm{mass}\mathrm{of}\mathrm{substance}}{\mathrm{Atomic}\mathrm{mass}\mathrm{of}\mathrm{atom}}\\ \mathrm{Number}\mathrm{of}\mathrm{moles}\mathrm{of}\mathrm{oxygen}& =& \frac{\mathrm{Given}\mathrm{mass}\mathrm{of}\mathrm{oxygen}}{\mathrm{Atomic}\mathrm{mass}\mathrm{of}\mathrm{oxygen}}\\ 0.2& =& \frac{\mathrm{Given}\mathrm{mass}\mathrm{of}\mathrm{oxygen}}{16}\\ \mathrm{Given}\mathrm{mass}\mathrm{of}\mathrm{oxygen}& =& 16\times 0.2=3.2\mathrm{g}\end{array}$

Hence, the mass of oxygen is 3.2 g.