Moles and masses - Higher
The massThe amount of matter an object contains. Mass is measured in kilograms (kg) or grams (g). of a substance can be calculated from the number of moleThe amount of substance that contains the same number of particles as there are atoms in 12 g of carbon-12 (contains the Avogadro's constant 6.0 脳10虏鲁 number of particles)., and the number of moles of a substance can be calculated from its mass. The link between the two quantities is the relative formula massThe sum of the relative atomic masses of the atoms in a chemical formula..
Calculating masses
Example
Calculate the mass of 0.25 mol of carbon dioxide molecules. (Mr of CO2 = 44)
Mass = relative formula mass 脳 amount
= 44 脳 0.25
= 11 g
Example 2
Calculate the mass of 0.10 mol of iron. (Ar of Fe = 56)
Mass = 56 脳 0.10
= 5.6 g
The calculation is the same if a substance is a metal or exists as separate atoms, but its Ar is used instead of an Mr.
Question
Calculate the mass of 0.10 mol of iron. (Ar of Fe = 56)
Mass = 56 脳 0.10
= 5.6 g
Calculating amounts in moles
Use Ar instead of Mr for metals or separate atoms.
Example
Calculate the amount of carbon atoms in 6.0 g of carbon. (Ar of C = 12)
Amount = \(\frac{\textup{mass}}{A_{\textup{r}}}\)
Amount = \(\frac{\textup{6.0}}{\textup{12}} \)
= 0.5 mol
Question
Calculate the amount of water molecules in 36 g of water. (Mr of water = 18)
Amount = \(\frac{mass}{relative~formula~mass}\)
Amount = \(\frac{\textup{36}}{\textup{18}} \)
= 2.0 mol