Question

Deduce the number of molecules of the following compounds in the given quantities.

32g oxygen, 90g water, 8.8g carbon dioxide, 7.1g chlorine.

Answer 1

a. 32 g of oxygen
$\mathrm{Number}\mathrm{of}\mathrm{moles}\mathrm{in}{\mathrm{O}}_2=\frac{\mathrm{Mass}\mathrm{of}{\mathrm{O}}_2\mathrm{in}\mathrm{grams}}{\mathrm{Molecular}\mathrm{mass}\mathrm{of}{\mathrm{O}}_2}$
$=\frac{32}{32}=1$mol
1 mole of O₂ contains-----6.022 x 10²³ molecules


b. 90 g of water
$\mathrm{Number}\mathrm{of}\mathrm{moles}\mathrm{in}water=\frac{\mathrm{Mass}\mathrm{of}water\mathrm{in}\mathrm{grams}}{\mathrm{Molecular}\mathrm{mass}\mathrm{of}water}$

$=\frac{90}{18}=5$moles
5 moles of H₂O contains-----5 x 6.022 x 10²³ molecules = 30.11 x 10²³ molecules

c. 8.8 g of CO_{2
$$\begin{gathered} \mathrm{Number}\mathrm{of}\mathrm{moles}\mathrm{in}{\mathrm{CO}}_2=\frac{\mathrm{Mass}\mathrm{of}{\mathrm{CO}}_2\mathrm{in}\mathrm{grams}}{\mathrm{Molecular}\mathrm{mass}\mathrm{of}{\mathrm{CO}}_2} \\ =\frac{8.8}{44}=0.2mol \end{gathered}$$}
0.2 moles of CO₂ contains-----0.2 x 6.022 x 10²³ molecules = 1.2044 x 10²³ molecules


d. 7.1 g of chlorine

$$\begin{gathered} \mathrm{No}.\mathrm{of}\mathrm{moles}\mathrm{in}\mathrm{chlorine}=\frac{\mathrm{Mass}\mathrm{of}\mathrm{chlorine}\mathrm{in}\mathrm{grams}}{\mathrm{Molecular}\mathrm{mass}\mathrm{of}\mathrm{chlorine}} \\ =\frac{7.1}{71}=0.1\mathrm{mol} \end{gathered}$$
0.1 moles of Cl₂ contains-----0.1 x 6.022 x 10²³ molecules = 0.6022 x 10²³ molecules