What is the empirical formula of a compund composed of 3.25% hydrogen(H), 19.36% carbon(C) and 77.39% oxygen(O) by mass?
To determine the empirical formula of a compound, you need to determine the ratio of the elements present in it. The percentage composition by mass provides the necessary information.
Here's how you can find the empirical formula of the compound:
1. Assume a 100-gram sample of the compound. This assumption allows us to work with percentages as grams directly.
2. Convert the mass percentages to grams:
- Hydrogen (H): 3.25% of 100 grams = 3.25 grams
- Carbon (C): 19.36% of 100 grams = 19.36 grams
- Oxygen (O): 77.39% of 100 grams = 77.39 grams
3. Calculate the number of moles for each element:
- Hydrogen (H): Moles = Mass (grams) / Molar mass (grams per mole). The molar mass of hydrogen is 1 g/mol.
Moles of H = 3.25 grams / 1 g/mol = 3.25 moles
- Carbon (C): Moles = Mass (grams) / Molar mass (grams per mole). The molar mass of carbon is 12 g/mol.
Moles of C = 19.36 grams / 12 g/mol = 1.61 moles
- Oxygen (O): Moles = Mass (grams) / Molar mass (grams per mole). The molar mass of oxygen is 16 g/mol.
Moles of O = 77.39 grams / 16 g/mol = 4.84 moles
4. Divide the number of moles of each element by the smallest number of moles obtained.
The smallest number of moles obtained is 1.61 moles (from carbon).
Dividing each number of moles by 1.61:
Moles of H = 3.25 moles / 1.61 moles = 2.02 (approximately)
Moles of C = 1.61 moles / 1.61 moles = 1
Moles of O = 4.84 moles / 1.61 moles = 3 (approximately)
5. The resulting ratio of moles gives us the empirical formula:
H₂C₃O₃
Therefore, the empirical formula of the compound is H₂C₃O₃.