To convert moles of a chemical substance to formula units, first convert moles into grams by using the molar masses of the elements that form the chemical compound. Every element in a chemical substance has its own molar mass, which is measured in grams.
Many chemical substances are compounds formed from combinations of moles of various elements. For example, 1 mole of sulphuric acid is made up of 2 moles of the element hydrogen, 1 mole of sulphur and 4 moles of oxygen. To find out the mass of this compound, first find the molar mass of each element that makes up the compound by referring to the periodic table.
To do the actual calculation of the compound, each element's molar mass is multiplied by the number of moles of the element that is found in the substance. For sulphuric acid, the molar mass of hydrogen is multiplied by 2, sulphur is multiplied by 1 and oxygen is multiplied by 4. Thus, the molar mass of sulphuric acid is equal to 2(1.008) + 32.06 + 4(16) = 98.08 grams.
When the moles have been converted into grams, it is easier to carry out calculations using the metric system. If necessary, conversions from metric to imperial units may be done. Also, conversion within the metric system of units may be done to allow more calculations.