Question

Consider separate samples of water and carbon dioxide, each with the same mass. Which contains the greater number of molecules?

Answer 1

Answer: The sample that contains the greater number of molecules is water.

Explanation: To calculate the number of molecules, it is used the Avogadro's number ( $6.02*10^{23}$ particles/molecules). So, considering that the mass to water and carbon dioxide is 1g (it can be any other number), the relationship between moles and molar weight is:

$moles =\frac{mass}{molar weight}$

To water: $moles = \frac{1g}{18 g/mol}$ = 0.05 moles.

Therefore,

1 mol ---- $6.02*10^{23}$ molecules

0.05 moles ---- x

x = $0.30*10^{23}$ molecules of water.

To carbon dioxide: $moles = \frac{1g}{44 g/mol}$ = 0.02 moles.

Therefore,

1 mol ---- $6.02*10^{23}$ molecules

0.02 moles ---- y

y = $0.12*10^{23}$ molecules of carbon dioxide.