Finding Empirical Formula Question

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In summary, the conversation discusses the process of finding the empirical formula of an organic compound extracted from a plant. The formula was determined by calculating the moles of hydrogen and carbon in the compound and using ratios to find the empirical formula. The discussion also addresses the presence of oxygen in organic compounds and how to calculate the empirical formula including oxygen.
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rudders93
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Homework Statement


A 2.203g sample of an organic compound was extracted from a plant. When it was burned in oxygen, the hydrogen in the compound was converted to 1.32g of water and the carbon was oxidised to 3.23g of CO2. Find the empirical formula of the compound

2. The attempt at a solution
So I found the number of moles of H2O that were reacted using the n = m/Mr formula (so m(H2O) = 1.32g, Mr(H2O) = 18g/mol therefore n(H2O) = 0.0733mol).

Also, I found then number of CO2 the same way, and came out nicely that n(CO2) = 0.0733mol

Here was my first problem. The ratio of n(H2O) : n(CO2) = 0.0733 : 0.0733, but since there are two H atoms in H2O does that mean there is the equivalent of 0.1466mol of H2O (ie: 2 * n(H2O)) or does it mean there are 0.03665mol of H2O (through: 0.5 * n(H2O)). Which one is it and why?

The second problem I had is this. The answer says that the empirical formula of the compound is: CH2O. What I don't see is how they found the number of O. Also, I'm confused as to how they knew there was O in the compound, does Organic mean it has O in it? Because I always thought that organic meant it had carbon, and that was the only prerequisite?

Thanks for your help!
 
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  • #2
That analysis only calculates C and H. Anything left over must be due to O.

1. Find the # grams of CO2 due only to carbon itself. (moles CO2/FW CO2)*(12grams C/ 1 mole C)

2. Repeat #1 using H2O.

3. Sum result of 1 & 2. Is it equal to 2.203 g? If not, what is missing?

4. Calculate moles of O.

5. Calculate empirical formula given results in 1, 2 & 4.
 

1. What is an empirical formula?

An empirical formula is the simplest whole number ratio of atoms in a compound. It shows the relative number of each type of atom in a molecule.

2. How do you find the empirical formula?

The empirical formula can be found by analyzing the mass percent composition of each element in a compound. The mass percent of each element can be converted to moles and then divided by the smallest number of moles to determine the ratio of elements in the compound.

3. Can the empirical formula be the same as the molecular formula?

Yes, the empirical formula can be the same as the molecular formula if the compound is a simple molecule with no subscripts. However, for more complex molecules, the empirical formula will be a simplified version of the molecular formula.

4. What is the difference between empirical and molecular formula?

The empirical formula shows the simplest whole number ratio of atoms in a compound, while the molecular formula shows the actual number of each type of atom in a molecule. The molecular formula can be a multiple of the empirical formula if the compound contains more than one molecule.

5. Why is finding the empirical formula important?

Finding the empirical formula is important because it gives insight into the chemical composition and structure of a compound. It is also useful in identifying unknown compounds and determining their properties and behavior.

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