Empirical Formula

The simplest formula or the empirical formula provides the lowest whole number ratio of atoms existent in a compound. The relative number of atoms of every element in the compound is provided by this formula.

Steps for Determining an Empirical Formula

• Let’s begin with what’s given in the problem, i.e., the number of grams of each element.
• We’ll assume that the total mass is 100 grams if percentages are given, so that

Each element’s mass = the given percentage

• By making use of the molar mass from the periodic table, change the mass of every element to moles.
• Divide every mole value by the lowest number of moles computed.
• Round up to the closest whole number.  This is denoted by subscripts in the empirical formula and is the mole ratio of the elements.

Multiply each answer by the same factor to get the lowest whole number multiple, if the number is too far to round off (x.1 ~ x.9).

e.g.  Multiply each solution in the problem by 4 to get 5, if one solution is 1.25.

e.g.  Multiply each solution in the problem by 2 to get 3, if one solution is 1.5.

The molecular formula can be calculated for a compound if the molar mass of the compound is given when the empirical formula is found.  To find the ratio between the molecular formula and the empirical formula. Basically, the mass of the empirical formula can be computed by dividing the molar mass of the compound by it.  Multiply every atom (subscripts) by this ratio to compute the molecular formula.