Calculations Involving Masses (1+2)

the simplest possible whole number ratio of atoms in each element within that compound

the actual number of atoms of each element within the compound

during a chemical reaction, no atoms are destroyed and no atoms are created this means that there are the same number and types of atoms on each side of a reaction equation

• Find the RFM of all the elements in the compound. • Divide the mass of each element by its RFM to find the moles of that element. • Write these moles as a ratio. • Divide each number in the ratio by the smallest number. • The smallest whole number ratio is the empirical formula. n = m/RFM

• Get a crucible and heat it until it’s red hot. • Leave the crucible to cool, then weigh it with its lid. • Add some clean magnesium ribbon to the crucible. • Reweigh the crucible, lid and magnesium ribbon. • Heat the crucible containing the magnesium. Put the lid on to stop any bits of solid from escaping, but leave a gap to allow oxygen to enter the crucible. • Keep heating the crucible strongly for abut 10 minutes, or until the magnesium ribbon has turned white. • Allow the crucible to cool and reweigh the crucible with the lid and contents. • Use the results to calculate the empirical formula of Magnesium Oxide.

mixtures that contain the solute dissolved in the solvent

the amount of substance in a certain volume of a solution

concentration = mass of solute / volume m = CV m: g C: g/dm^3 V: dm^3

the reactant that’s used up, causing the reaction to stop this limits the amount of product that is formed

6.02 x 10^23

the amount of that substance that contains 6.02 x 10^23 particles (these particles could be atoms, molecules or ions)

moles = mass / RFM n = m / RFM n: mol m: g