Percentage Composition and Empirical Formula

Question 1

What is empirical formula?

Answer 1

The simplest whole number ratio of each type of atom in a compound.

Question 2

How do we work out empirical formula?

Answer 2

• Write the mass of each element
• Find the Ar of each element
• Find how many moles there are in each element by doing mass/Mr
• Find the smallest value of moles
• Divide each element by the smallest value of moles

Question 3

What would be the empirical formula of 2.45g of sulphuric acid with 0.05g hydrogen, 0.8g sulphur and 1.6g oxygen?

Answer 3

• H = 0.05g, S = 0.8g, O = 1.6g
• H = 1, S = 32, O = 16
• (Moles) H = 0.05, S = 0.025, O = 0.1
• S is the smallest
• (Dividing by S) H = 2, S = 1, O = 4
• Empirical formula = H2SO4

Question 4

How can we calculate % mass?

Answer 4

• (Mass of desired/mass of compound)X100

OR

• (Ar of element/Mr of compound) X100

Question 5

How do we calculate empirical formula from %?

Answer 5

Work in the same way but with 100g of the substance and follow the same steps as before.