For example, given the formula for octane C8H18 What would be the empirical formula of this compound? How many times would this repeating unit repeat itself to make up the true compound?
The Correct Answer and Explanation is:
The molecular formula of octane is C8H18. To find its empirical formula, we first need to determine the simplest whole-number ratio of carbon atoms (C) to hydrogen atoms (H).
Step-by-Step Calculation:
- Identify the number of atoms in the molecular formula:
- The molecular formula for octane is C8H18, meaning it has 8 carbon atoms and 18 hydrogen atoms.
- Find the greatest common divisor (GCD):
- The greatest common divisor of 8 (the number of carbon atoms) and 18 (the number of hydrogen atoms) is 2.
- Divide each atom count by the GCD:
- For carbon: 8 ÷ 2 = 4
- For hydrogen: 18 ÷ 2 = 9
- Write the empirical formula:
- The empirical formula is C4H9.
Explanation of the Empirical Formula:
- The empirical formula, C4H9, represents the simplest ratio of carbon to hydrogen atoms in the compound. This is not the molecular formula, but rather the smallest repeating unit that forms the molecular structure of octane.
Repeating Unit:
- To get the molecular formula from the empirical formula, we see how many times the empirical unit (C4H9) must be repeated to match the molecular formula. The molecular formula is C8H18, and if we multiply the empirical formula (C4H9) by 2, we get C8H18.
Therefore, the empirical formula is C4H9, and the repeating unit (C4H9) repeats 2 times to form the true compound, octane (C8H18).
This demonstrates how the empirical formula provides the simplest possible ratio while the molecular formula gives the actual composition of the molecule.
