2. Combustion Analysis

3. Ex - Find the empirical formula of vitamin C (ascorbic acid), a compound that contains only C, H, and O. Combustion of 1.000 g of vitamin C produced 1.500 g of CO 2 and 0.405 g of H 2 O.

4. 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 1.500 g of CO 2 and determine the mass of carbon in it.

5. All of the hydrogen is incorporated into the water. We can take the 0.405 g of water and calculate the amount of hydrogen it contains.

6. Oxygen is added to the reaction so we must get the oxygen by subtraction from the mass of the original compound. 1.000 g – 0.4093 g C – 0.0454 g H = 0.5453 g O

7. Now we can do a regular empirical formula problem. CHO 0.4093 g0.0454 g0.5453 g Divide by each atomic weight to get moles / 12.01/ 1.01/16.00 = 0.03408= 0.04495= 0.03408

8. Divide each by the smallest to find the whole number ratio. /0.03408/.03408 = 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