## Test #1 Question 7 mass percentage

Nabeeha Khan 1D
Posts: 30
Joined: Fri Apr 06, 2018 11:03 am

### Test #1 Question 7 mass percentage

Question 7: Determine the empirical formula for an organic compound that when burned in the presence of oxygen formed 69.4g CO2 and 17.05g of H2O. What is the mass percentage of carbon and hydrogen in the sample?

Does anyone have the correct answers for this problem?

Sara Veerman-1H
Posts: 31
Joined: Fri Apr 06, 2018 11:05 am

### Re: Test #1 Question 7 mass percentage

Yeah, this is a tricky question because the amount of O2 that reacted was not given. First I divided both amounts of CO2 and H2O formed by their respective molar masses and found that they were equal to each other (both created 0.178 moles). Using this knowledge and the fact that O2 was present I created the formula x + O2 --> H2O + CO2. Balancing the equation gave me CH2O + O2 --> H2O + CO2. So the empirical formula for the sample is CH2O. In order to find the mass percentage I assumed 1.00 moles of the sample was used, so there is 1 mol C, 2 mol H, and 1 mol O. Dividing those numbers by their molar mass will give you: 12.01 g C, 16.00 g O, and 2.00 g H. Then I just divided these masses by the total mass of the sample (the total mass is the moles of the sample divided by its molar mass) and I was able to get the percentages. I'm not sure if I did this right. I remember my TA saying something along the lines that not enough information was provided and free points were given and its probably only because of that I got full points on this particular problem... But I hope this helps