Emperical Formula - Explanation and Worked Examples of Emperical Formula

len Alfred Ajibola - Sat, 16th March, 2019 @ 11:00: AM

Topics in Chemistry

Elements, Compounds and Mixtures with their Characteristics Salts and Types of Salt in Chemistry Mixtures and Separation of Mixtures Mixtures and Separation of Mixtures - part 2 Mixtures and Separation of Mixtures - part 3 Physical and Chemical Change explained with their Differences Electrolysis, Electrolyte, Electrode, Anode, Cathode and Ionic Theory Diffusion - Grahams Law of diffusion and Importance of Graham's Law of Diffusion Metals - Physical Properties of Metals Daltons Atomic Theory and its Modifications Periodic table: Classification of Elements in the Periodic Table Emperical Formula - Explanation and Worked Examples of Emperical Formula Organic Chemistry - Hydrocarbon, Carbon and its Compounds Explanation, Worked Examples and Differences between Molecular Mass and Molar Mass Gold: Interesting Facts about Gold Matter, Mass, Weight and Characteristics of Solids, Liquids, Gases Acids - Definitions of Acids, Physical and Chemical properties of Acids

Academic Questions in Chemistry

Please check out our Test Your Knowledge page to see all Questions and Answers

The reaction involving an acid and a base is termed _____.

  • A. Hydrolysis
  • B. Neutralization
  • C. Combustion
  • D. Displacement
  • E. Decomposition
  • F. Sublimation

Which of the following is NOT a type of salt?

  • A. Acid salt
  • B. Basic salt
  • C. Double salt
  • D. Tripple salt
  • E. Complex salt
  • F. Normal Salt

The only metal that exist as liquid at room temperature is _____.

  1. Nickel
  2. Duralumin
  3. Mercury
  4. Lead
  5. Titanium
  6. Cesium

Empirical Formula:

Let's begin by considering two atoms, say Hydrogen (H) and oxygen (O). If these atoms are combined to form a compound, let's say (HO) for instance, we will not be able to tell the ideal formula of the compound if this was an experimental sample; as it also could be H2O, H2O2 or something else.

With regards to the uncertainty of the compound formed in the above instance, the empirical formula comes into play. It is the simplest formula of a compound because it is derived from experimental data or analysis.

It is the empirical formula that tells us the relative ratios the of different atoms in a compound.

Please read on Matter, Mass and Weight here.

The empirical formula of a compound may be defined as the formula that shows only the relative number of atoms of each element present in the compound.


Now let's consider water molecule (H2O) as a reference:

H2O = 2 atoms of hydrogen (H) and 1 atom of oxygen (O).

H2O = 1 mole of hydrogen molecule and 1 mole of oxygen.

Please read on Molecular Mass and Molar Mass here.

Note: Always remember that when a number isn't written in front of a compound, then it means that the number "1" is actually in front of that compound. So, the H2O in our above example is actually 1H2O (1 mole of water).

The 1 (in front of the compound) is referred to as the Mole Ratio.

Therefore, if we know the amounts of mole of each element in a compound, then the emperical formula can be determined.

Note: Whenever we are working with the percentages of each element contained within a compound, we will need to convert the percentages into the mole ratio of the elements in order to get the empirical formula of the compound.

Please read on Graham's Law of Diffusion here.


Worked Example of Emperical Formula:

A compound composed of iron (Fe) and oxygen (O) was analyzed and found to contain 69.94% iron and 30.06% oxygen. Find the empirical formula of the compound. ( Molar mass of Fe=55.85, O=16)


Step 1: Identify the given parameter from the question.

Fe = 69.94%,   O = 30.06%.

Empirical formula = Fe?O?


Step 2: Convert the percentages to gram. (just attribute grams to the %).

69.94% = 69.94g while 30.06% = 30.06g


Step 3: To get the mole ratio of each element, convert the gram to moles using the formula (mole = mass/molarmass). Please merorize this formula because we always work with moles in Emperical Formula.

Mole of Fe: 69.94/55.85 = 1.252mol

Mole of O: 30.06/16 = 1.879mol


Step 4: Divide both sides by the smallest mole ratio.

Iron has the smallest mole ratio in our case, therefore: 1.252/1.252 = 1,    1.879/1.252 = 1.5

We now have the formula = Fe1O1.5


Step 5: Multiply each of the moles by the smallest whole number that will convert each into a whole number. (In our case, the number "2" is the smallest whole number that will make "1.5" and "1" whole numbers when multiplied by it.

For iron (Fe), we will have 1 x 2 = 2

For oxygen (O), we will have 1.5 x 2 = 3


Step 6: Write the empirical formula.

The empirical formula= Fe2O3


THANKS FOR READING - Please Help Share!


Alfred Ajibola is a Medical Biochemist, a passionate Academician with over 7 years of experience, a Versatile Writer, a Web Developer, a Cisco Certified Network Associate and a Cisco CyberOps Associate.

Amazing facts in Chemistry

The only letters that failed to appear on the periodic table are letters:

J     &     Q

Gold and copper are the only two non-silvery colored metals. Please read some interesting facts about gold here

Copper is the only metal that is naturally antibacterial. This is why you would see some children carry copper water bottles to school

Water actually freezes faster when it’s warm than when it’s cold

Most element in their pure state exists physically in different forms. For instance, pure carbon can exist as both diamond and graphite. This phenomenon is called allotropy.
Please read on modification of Dalton's atomic theory here.

If you pour a handful of salt into a full glass of water, the water level will go down rather than overflowing the glass.

Similarly, if you mix half liter of water and half litre of alcohol, the total volume of the liquid will be les than one litre