Quantitative chemistry

Conservation of mass

The law of conservation of mass states that atoms cannot be created or destroyed in a chemical reaction. Instead they are rearranged into new substances.

This means that when measuring the mass of a reaction you would expect the mass at the start to be the same as the mass at the end. However sometimes the mass can change.

The relative formula mass ( M _r ) of a compound is the sum of the relative atomic masses of the atoms in the numbers shown in the formula.

Decrease in mass

In some reactions the mass appears to decrease. This is because a gas is produced and lost to the surroundings.

Increase in Mass

The mass can also appear to increase. This is because one of the reactants is a gas meaning they form a compound.

Concentration is the amount of solvent in a volume of solute.

Concentration = mass / vol

Lots of solute in little solution = high concentration

Little solute in high concentration = low concentration