Question

Calculate the mass of sodium which contains same number of atoms as are present in $20gofCa$. (atomic mass $\mathrm{Ca}=40,\mathrm{Na}=23$)

Answer 1

• Given, Mass of $\mathrm{Ca}$= $20\mathrm{g}$
• Moles of Calcium= Given mass/ Molar mass

=$\frac{20}{40}=0.5mol$

• 1 mole of $\mathrm{Ca}$= $6.022\times {10}^{23}=40g$
• $0.5moleofCacontains=0.5\times 6.022\times {10}^{23}=3.01\times {10}^{23}$
• Hence, the number of atoms of $\mathrm{Na}$ = $3.01\times {10}^{23}$
• Moles of $\mathrm{Na}$ = Given number of atoms/ $6.022\times {10}^{23}$

= $3.01\times {10}^{23}/6.022\times {10}^{23}=0.5mol$

• Mass of $\mathrm{Na}$= moles * molar mass =$0.5\times 23=11.5g$
• Thus, the mass of sodium that contains the same number of atoms as are present in $20\mathrm{g}\mathrm{of}\mathrm{Ca}=11.5\mathrm{g}$