Combustion Analysis

Ex - Find the empirical formula of vitamin C (ascorbic acid), a compound that contains only C, H, and O. Combustion of g of vitamin C produced g of CO 2 and g of H 2 O.

The general reaction is: CxHyOz + O 2  CO 2 + H 2 O So, all of the carbon in the compound is incorporated into the carbon dioxide. We can take the g of CO 2 and determine the mass of carbon in it.

All of the hydrogen is incorporated into the water. We can take the g of water and calculate the amount of hydrogen it contains.

Oxygen is added to the reaction so we must get the oxygen by subtraction from the mass of the original compound g – g C – g H = g O

Now we can do a regular empirical formula problem. CHO g g g Divide by each atomic weight to get moles / 12.01/ 1.01/16.00 = = =

Divide each by the smallest to find the whole number ratio. / / = 1= 1.32= 1 Multiplying each by 3 will give whole numbers. The compound is then C 3 H 4 O 3. Click here to take the quiz