d) relative formula masses and molar volumes of gases Flashcards
1.16- calculate relative formula masses (Mr) from relative atomic masses (Ar)
1) Write the formula of the compound.
2) Write the numbers of each atom in the formula.
3) Insert the relative atomic mass for each type of atom.
4) Calculate the total mass for each element.
5) Add up the total mass for the compound.
E.g. water- H20 - 1+1+16= 18 RFM- 18
1.17- understand the use of the term mole to represent the amount of substance
A mole is a certain amount of substance. It is a general term to describe an amount of atoms, ions or molecules.
1.19- carry out mole calculations using relative atomic mass (Ar) and relative formula mass (Mr)
A mole of a molecular compound contains 6 x 1023 molecules. It has a mass that is equal to its relative formula mass.
So a mole of water (H2O) has a mass of 18 g. A mole of carbon dioxide (CO2) has a mass of 44 g. This also works for ionic compounds, so a mole of sodium chloride (NaCl) has a mass of 58.5 g.
For example, oxygen gas O2 is diatomic (each molecule contains two atoms) so its relative formula mass is 32. One mole of oxygen molecules would therefore have a mass of 32 g. One mole of oxygen atoms (if you could ever isolate them) would have a mass of 16 g.
