Finding Emperical Formulas?

Question

A carbohydrate (consists of carbon, hydrogen, and oxygen ) is burned in oxygen producing only carbon dioxide and water vapor. Burning 2.15 g of this carbohydrate produces 3.53 g of CO2 and 1.44 g of H2O. Find the emperical formula of this carbohydrate.

Answer 1

First, you'll convert the mass of CO2 produced into moles using the molecular weight of CO2. That will give you the moles of C present in your sample.

Next, take the mass of water and divide that by water's molecular weight to get the moles of water. Multiply that by 2 to get the moles of hydrogen in the compound. If you then divide the moles of H by the moles of C, you get the ratio of those two elements in the original compound.

In order to find the amount of oxygen, you'll need to take the moles of C that you got in the first part and convert that to grams. Do the same thing with the moles of H from the second part, then add those two masses together.

Since your original compound consists only of C H and O, the difference between the mass you just calculated and the original mass of your sample is the mass of oxygen. Convert that mass into moles, divide that by the moles of carbon in the sample, and you'll have the ratio of C to O.

That'll let you determine the empirical formula of the compound.

Answer 2

Carbohydrates have the genreal formula -(CH2O)n- where n=3,9

The most common are n=5, 6 so start there.

You will have to do a little calculating to see if your figures match the formulas for the proposed structures (write down balanced equations, figure out MW's, and convert to grams, to get amount of products from each structure).

Hope this helps.

Answer 3

Moles of H2O = 1.44/18 = .08

So moles of H = .16

Moles of CO2 = 3.53/44 = 0.08

Moles of C= 0.08

General formula of carbohydrate = Cx(H2O)y

x=y as 0.16 = 2x0.08

Thus empirical formula is CH2O

Answer 4

yes that formula is correct..

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