Combustion analysis is a simple technique used to find the empirical formula of a compound – often an organic or carbon based molecule. Essentially, the sample is weighed and then burnt to a crisp in excess oxygen, and the masses of each of the elements present in the sample can be determined from the masses of the product gases.
The video shows you the method for solving combustion analysis problems. You’ll find plenty of simple questions to practice on in your text book but there is an opportunity to practice a couple of more difficult examples at the end of this post!
Practice questions
- A sample of a compound weighing 0.1005g and containing only carbon, hydrogen and oxygen underwent combustion analysis to give 0.2829g of carbon dioxide and 0.1159g of water. Determine the empirical formula.
- A sample of a compound weighing 0.2417g and containing only carbon, hydrogen, oxygen and chlorine underwent combustion analysis to give 0.4964g of carbon dioxide and 0.0846g of water.
A second sample, this one weighing 0.1696g, was reacted to liberate the chlorine in the form of chloride ions which were precipitated from solution as 0.1891g of silver chloride (AgCl).
Determine the empirical formula of the original sample.
Answer to Q1
Answer to Q2
