A compound of molecular weight 70.1 has the following composition: Carbon 85.63% and hydrogen 14.37%. What is the empirical formula? What is the molecular formula?
70.1*.8563/12 = 5.00 moles C
70.1*.1437/1 = 10.07 moles H
empirical CH2 has mol wt 14
70.1/14 = 5, so
molecular formula is C5H10
To determine the empirical formula, you'll need to find the simplest whole number ratio of the elements in the compound. Here's how to calculate it:
1. Convert the mass percentage of each element to moles:
- Carbon (C): 85.63 g / 12.01 g/mol = 7.13 moles
- Hydrogen (H): 14.37 g / 1.01 g/mol = 14.23 moles
2. Determine the ratio of the elements by dividing the moles of each element by the smallest number of moles:
- C: 7.13 moles / 7.13 moles = 1
- H: 14.23 moles / 7.13 moles ≈ 2
3. Write down the empirical formula using the whole number ratio:
CH2
The empirical formula is CH2.
To determine the molecular formula, you'll need the molecular weight of the compound. Since the compound's molecular weight is given as 70.1 g/mol, divide this by the empirical formula weight to find the multiples:
4. Calculate the empirical formula weight:
- C: 1 × 12.01 g/mol = 12.01 g/mol
- H: 2 × 1.01 g/mol = 2.02 g/mol
Empirical formula weight = 12.01 g/mol + 2.02 g/mol = 14.03 g/mol
5. Divide the molecular weight by the empirical formula weight to find the multiple:
70.1 g/mol / 14.03 g/mol ≈ 5
6. Multiply the subscripts in the empirical formula by the multiple calculated:
C × 5 = 5C
H × 5 = 10H
The molecular formula is C5H10.
To determine the empirical formula, we need to find the simplest ratio of atoms in the compound.
First, we need to convert the percentages of carbon and hydrogen into moles. To do this, assume we have 100g of the compound.
The mass of carbon in 100g of the compound can be calculated as:
Mass of carbon = 85.63% * 100g = 85.63g
The mass of hydrogen in 100g of the compound can be calculated as:
Mass of hydrogen = 14.37% * 100g = 14.37g
Next, we need to convert the masses of carbon and hydrogen into moles using their respective atomic masses.
The atomic mass of carbon (C) is approximately 12.01g/mol, and the atomic mass of hydrogen (H) is approximately 1.01g/mol.
Number of moles of carbon = Mass of carbon / Atomic mass of carbon
Number of moles of carbon = 85.63g / 12.01g/mol = 7.13 mol
Number of moles of hydrogen = Mass of hydrogen / Atomic mass of hydrogen
Number of moles of hydrogen = 14.37g / 1.01g/mol = 14.23 mol
We now have the ratio of carbon to hydrogen as approximately 7.13:14.23, which can be simplified to 1:2 by dividing each number by 7.13.
Therefore, the empirical formula is CH2.
To find the molecular formula, we need to know the molar mass of the compound.
The molar mass of the compound is given as 70.1 g/mol.
Now, we need to compare the molar mass of the empirical formula (CH2) to the molar mass of the compound.
The molar mass of CH2 is approximately 14.03 g/mol (12.01 g/mol for carbon + 2 * 1.01 g/mol for hydrogen).
To find how many empirical formula units are in the molecular formula, we can divide the molar mass of the compound by the molar mass of the empirical formula:
Number of empirical formula units = Molar mass of compound / Molar mass of empirical formula
Number of empirical formula units = 70.1 g/mol / 14.03 g/mol ≈ 5
Therefore, the molecular formula is (CH2)5, which can be simplified as C5H10.