An organic compound contains 49.2% Carbon, and 9.68% Hydrogen and 19.19% Nitrogen. If Molecular Mass of compound is 146. Calculate the Molecular Formula of compound.
mols C = 49.2/12 = ?
mols H = 9.68/1 = ?
mols N = 19.19/14 = ?
BUT C+H+N doesn't add to 100%. You made a typo or omitted something or the author of the problem forgot something.
To determine the molecular formula of the compound, we need to find the empirical formula first. The empirical formula represents the simplest whole number ratio of the atoms present in a compound.
Step 1: Convert the percentages of each element to moles.
Assume we have 100g of the compound, which means that we have:
- 49.2g of Carbon
- 9.68g of Hydrogen
- 19.19g of Nitrogen
To convert these masses to moles, we'll need the molar masses of each element:
- Carbon: 12.01 g/mol
- Hydrogen: 1.01 g/mol
- Nitrogen: 14.01 g/mol
Moles of Carbon = 49.2g / 12.01 g/mol ≈ 4.099 mol
Moles of Hydrogen = 9.68g / 1.01 g/mol ≈ 9.603 mol
Moles of Nitrogen = 19.19g / 14.01 g/mol ≈ 1.370 mol
Step 2: Find the simplest whole number ratio of the atoms.
To do this, divide each mole value by the smallest number of moles (1.370 mol in this case):
Carbon: 4.099 mol / 1.370 mol ≈ 3
Hydrogen: 9.603 mol / 1.370 mol ≈ 7
Nitrogen: 1.370 mol / 1.370 mol = 1
The empirical formula is C3H7N.
Step 3: Calculate the empirical formula mass.
The empirical formula mass is the sum of the atomic masses of all the atoms in the empirical formula.
Empirical Formula Mass = (Atomic Mass of C * number of C atoms) + (Atomic Mass of H * number of H atoms) + (Atomic Mass of N * number of N atoms)
Empirical Formula Mass = (12.01 g/mol * 3) + (1.01 g/mol * 7) + (14.01 g/mol * 1)
Empirical Formula Mass = 36.03 g/mol + 7.07 g/mol + 14.01 g/mol
Empirical Formula Mass ≈ 57.11 g/mol
Step 4: Find the multiple to reach the molecular mass.
To find the molecular formula from the empirical formula, divide the molecular mass by the empirical formula mass:
Multiple = Molecular Mass / Empirical Formula Mass
Multiple = 146 g/mol / 57.11 g/mol ≈ 2.559
Step 5: Multiply the empirical formula by the multiple.
Multiply the subscripts of each element in the empirical formula by the calculated multiple to find the molecular formula:
Molecular Formula = (C3H7N)2.559
Molecular Formula ≈ C7.677H17.953N2.559
Since we cannot have fractional subscripts in a molecular formula, we need to round the subscripts to the nearest whole number:
Molecular Formula = C8H18N3
Therefore, the molecular formula of the compound is C8H18N3.