Question

Determine the mass of 5.2 x 10 power of 21 molecules of propanol C3H7OH(l), on grams.

Answer 1

`n(\text{C}_3\text{H}_7\text{OH}) = N(\text{C}_3\text{H}_7\text{OH}) / N_A\\ \phantom{n(\text{C}_3\text{H}_7\text{OH})} = 5.2 * 10^(21) / (6.02 * 10^(23))\\ \phantom{n(\text{C}_3\text{H}_7\text{OH})} = 8.6 * 10^(-3) \; \text{mol}`

where
`N_A = 6.02 * 10^(23)\; \text{mol}^(-1)` the Avogadro's constant that relates the number of particles to their number, in the unit moles
`\text{mol}`.

The molar mass of propanol- mass per mole propanol- can be directly deduced from its molecular formula with reference to a modern periodic table.

`M(\text{C}_3\text{H}_7\text{OH}) = \underbrace{3 * 12.01}_{\text{carbon}} + \underbrace{8 * 1.008}_{\text{hydrogen}} + \underbrace{1* 16.00}_{\text{oxygen}} = 60.09 \; \text{g} \cdot \text{mol}^(-1)`

`8.6 * 10^(-3) \; \text{mol}` of propanol molecules would thus have a mass of
`8.6 * 10^(-3) \; \text{mol} * 60.09 \; \text{g} \cdot \text{mol}^(-1) = 0.52 \; \text{g}`