Number of molecules in 3.5g H?O, 56.1g N?, 89g CCl?, 19g C?H??O?

Step 1 of 4

To determine the number of molecules in each sample, we use the concept of moles. One mole of any substance contains Avogadro's number, approximately \(6.022 \times 10^{23}\), of its elementary entities, which can be atoms, molecules, ions, etc.

We first convert the mass of the substance to moles using the molar mass, then we multiply it by Avogadro's number.

 (a) we have 3.5 g of water \(\mathrm{H}_{2} \mathrm{O}\)

Calculating the molar mass of of \mathrm{H}_{2} \mathrm{O}\)

\(\begin{aligned} \text { molar mass } & =1 \times(16.00)+2 \times(1.008) \\ & =16+2.016 \\ & =18.02 \mathrm{~g} / \mathrm{mol} \end{aligned}\)

Calculating the number of molecules in 3.5 g of \(\mathrm{H}_{2} \mathrm{O}\)

\(\left(\frac{3.5}{18.02}\right) \times 6.022 \times 10^{23} = 1.17 \times 10^{23}\)

Therefore, 3.5 g of of \(\mathrm{H}_{2} \mathrm{O}\) contains \(1.17 \times 10^{23}\) molecules of \(\mathrm{H}_{2} \mathrm{O}\).