An organic compound is known to contain only carbon, hydrogen and oxygen - VCE - SSCE Chemistry - Question 11 - 2005 - Paper 1

Next, we need to convert each of the mass percentages into moles. We divide by the molar mass of each element:

• Molar mass of Carbon (C) = 12.01 g/mol
• Molar mass of Hydrogen (H) = 1.008 g/mol
• Molar mass of Oxygen (O) = 16.00 g/mol

Calculating the moles:

• Moles of Carbon: $\frac{39.1 \, g}{12.01 \, g/mol} \approx 3.26 \, mol$
• Moles of Hydrogen: $\frac{8.7 \, g}{1.008 \, g/mol} \approx 8.63 \, mol$
• Moles of Oxygen: $\frac{52.2 \, g}{16.00 \, g/mol} \approx 3.26 \, mol$

Now, we find the simplest mole ratio by dividing each number of moles by the smallest number of moles calculated:

• For Carbon: $\frac{3.26}{3.26} = 1$
• For Hydrogen: $\frac{8.63}{3.26} \approx 2.64$
• For Oxygen: $\frac{3.26}{3.26} = 1$

The ratio of C:H:O is approximately 1:2.64:1. We can round 2.64 to 3 for simplicity. Hence, the approximate ratio is 1:3:1.

From the empirical formula ratio C:H:O = 1:3:1, we can see that the number of carbon atoms in the empirical formula is 1.

However, upon reviewing the values of moles, we can also calculate the total ratio based on C and H which dictates that the empirical formula must depict the simplest regular integer ratio. Thus, the final conclusion is that the number of carbon atoms in the empirical formula is 3.