Relative formula masses can be calculated and used in conservation of mass calculations.
Calculations can be carried out to find out concentrations of solution and uncertainties in measurements.
Relative formula mass is the smallest part of an element that can exist.
Mass is measured in kilograms (kg) or grams (g).
The relative atomic mass of an element is the mean relative mass of the atoms of the different isotopes in an element.
The relative atomic mass of an element is the number of times heavier an atom is than one-twelfth of a carbon-12 atom.
The relative atomic mass of an element, A r, is the relative mass of its atoms compared to the mass of a carbon-12 atom.
The A r values for elements are given in the periodic table.
Since A r is a measure of relative mass, it has no units.
The atomic structure study guide explains how to calculate relative atomic mass.
The relative formula mass of a substance made up of molecules is the sum of the relative atomic masses of the atoms in the numbers shown in the formula.
Relative formula mass, M r , is represented by the symbol.
To calculate the M r for a substance, work out how many atoms of each element there are in the chemical formula and add together the A r values for all the atoms of each element present.
The formula for carbon dioxide is CO 2 and it consists of one carbon atom ( A r = 12) and two oxygen atoms ( A r = 16), resulting in a relative formula mass, M r , of 44.
Like A r values, M r values are just numbers with no units because they are relative masses.
An ionic compound occurs when a negative ion (an atom that has gained an electron) joins with a positive ion (an atom that has lost an electron), such as sodium chloride, which do not exist as molecules.
The relative formula mass of an ionic compound is calculated in the same way as for molecules, from the numbers shown in the formula.
The relative formula mass of calcium hydroxide, Ca(OH) 2 , can be calculated as 40 + (2 × 16) + (2 × 1) = 40 + 32 + 2 = 74.
The relative formula mass of magnesium nitrate, Mg(NO 3 ) 2 , can be calculated as 24 + (2 × 14) + (2 × 3 × 16) = 24 + 28 + 96 = 148.
The law of conservation of mass states that matter cannot be created or destroyed.