Questions
1. What is an empirical formula?
2. Find the empirical formula of the iron oxide produced when 44.8g of iron react with 19.2g of oxygen. (Ar for iron = 56, Ar for oxygen=16)
3. A sample of an organic hydrocarbon was burnt completely in air. 4.4g of carbon dioxide and 1.8g of water were formed.
Work out the empirical formula of the hydrocarbon.
4. 60g of calcium react with 106.5g of chlorine to produce calcium chloride. Calculate the empirical formula of calcium chloride. Show all your working.
(Relative atomic masses: Ca= 40, Cl= 35.5)
5. Find the empirical formula of the compund formed when 21.9g of magnesium, 29.2g of sulfur and 58.4g of oxygen react.
6. A sample of calcium hydroxide was found to contain, by mass, 54.1% calcium, 43.2% oxygen and 2.7% hydrogen.
Calculate the empirical formula of the calcium hydroxide. Show your working.
7. A compound contains 28.8g of carbon and 76.8g of oxygen. What is the empirical formula of the compound? Show your working.
(Relative atomic masses: C=12, O=16)
1.It shows the simplest ratio in which atoms combine
2. Fe2O3
3. CH2
4. Ca=40 Cl= 35.5
60/40 106.5/35.5
= 1.5 = 3
1.5/1.5=1 3/1.5=2
5. MgSO4
6. Ca O H
54.1/40 43.2/16 2.7/1
=1.35 =2.7 =2.7
=1.35/1.35 =2.7/1.35 =2.7/1.35
=1 =2 =2
So the empirical formula can be CaO2H2 or Ca(OH)2
7. C= 28.8 O= 76.8
28.8/12 76.8/16
=2.4 =4.8
2.4/2.4=1 4.8/2.4=2
The empirical formula is CO2.