Question

Calculate the mass of the$1.51\times {10}^{23}\mathrm{molecules}\mathrm{of}\mathrm{water}$

Answer 1

$\mathrm{Molecular}\mathrm{mass}\mathrm{of}{H}_{2}O=18\mathrm{Number}\mathrm{of}\mathrm{moles}=\frac{\mathrm{Number}\mathrm{of}\mathrm{molecules}\mathrm{of}\mathrm{water}}{\mathrm{Avogadro}’s\mathrm{number}}=\frac{1.51\times {10}^{23}}{6.023\times {10}^{23}}=\frac{1}{4}=0.25\mathrm{mole}\mathrm{Number}\mathrm{of}\mathrm{moles}=\frac{\mathrm{Mass}}{\mathrm{Molecular}\mathrm{mass}}0.25=\frac{\mathrm{mass}}{18}\mathrm{Mass}=0.25\times 18\mathrm{Mass}=4.5g$