Calculate the molecular formula of a compound whose empirical formula is CH2O AND vapour density is 30
C2H4O2
To calculate the molecular formula of a compound, you need to know the empirical formula and the molar mass of the compound. In this case, you have the empirical formula of CH2O and the vapor density.
Step 1: Determine the empirical formula molar mass
The empirical formula of CH2O consists of one carbon (C), two hydrogen (H), and one oxygen (O) atom. To calculate the empirical formula molar mass, add up the atomic masses of each element:
C = 12.01 g/mol
H = 1.008 g/mol
O = 16.00 g/mol
Empirical formula molar mass:
(12.01 g/mol * 1) + (1.008 g/mol * 2) + (16.00 g/mol * 1) = 30.03 g/mol
Step 2: Determine the molar mass of the compound
The vapor density is the ratio of the molar mass of the compound to the molar mass of hydrogen gas (2.016 g/mol).
Vapor density:
Molar mass of the compound / Molar mass of hydrogen gas = 30 / 2.016 = 14.9
Step 3: Determine the molecular formula
To find the molecular formula, divide the molar mass of the compound by the empirical formula molar mass and round to the nearest whole number:
14.9 g/mol / 30.03 g/mol ≈ 0.497
This result suggests that the molecular formula is approximately half the size of the empirical formula.
Multiply the subscripts in the empirical formula by the calculated factor (0.497):
C = 1 * 0.497 ≈ 0.497 ≈ 0.5
H = 2 * 0.497 ≈ 0.994 ≈ 1
O = 1 * 0.497 ≈ 0.497 ≈ 0.5
Therefore, the molecular formula of the compound is approximately C0.5H1O0.5. Since you can't have fractional subscripts, multiply each subscript by 2 to get whole numbers:
C = 2 * 0.5 = 1
H = 2 * 1 = 2
O = 2 * 0.5 = 1
Hence, the molecular formula of the compound is CHO2.