Question

Calculate the number of moles (of molecules) in the following samples.(Avogadro's # = 6.02 x 1023 molecules per mole)
(A) 9.93 g H2O

Answer 1

Question #46953 – Chemistry – Inorganic Chemistry

Question:

Calculate the number of moles (of molecules) in the following samples. (Avogadro's # = 6.02 x 10²³ molecules per mole)

(A) 9.93 g H₂O

Answer:

The mass of one atom of hydrogen is 1.67 × 10⁻²⁴ g, the mass of one atom of oxygen is 26.72 × 10⁻²⁴ g. Hence, the mass of one H₂O molecule is:

$$\mathrm{m(H_2O)} = 2 \times (1.67 \times 10^{-24} \mathrm{g}) + 26.72 \times 10^{-24} \mathrm{g} = 30.06 \times 10^{-24} \mathrm{g}.$$

One mole contains 6.02 × 10²³ molecules of water, therefore the mass of one mole is:

$$\mathrm{M(H_2O)} = 30.06 \times 10^{-24} \mathrm{g} \times 6.02 \times 10^{23} \mathrm{mol}^{-1} = 18.096 \mathrm{g/mole}$$

We have 9.93 g, so corresponding the number of moles can be estimated:

$$\mathrm{N(H_2O)} = \mathrm{m_x(H_2O)/M(H_2O)} = 9.93 \mathrm{g}/18.096 \mathrm{g/mole} = 0.55 \mathrm{moles}$$