a hydrocarbon has an empirical formula CH and a vapour density of 39. Determine its molecular formula. solution.................................................... CH=12+1
n=13
13n=39
=3
almost...
vapour density is relative to H2.
So
M~2*vapour density=78.
chemistry
To determine the molecular formula of the hydrocarbon, we need to calculate the molar mass of the empirical formula CH and compare it to the given vapour density.
The empirical formula CH represents one carbon atom (C) and one hydrogen atom (H). The atomic mass of carbon (C) is 12 g/mol, and the atomic mass of hydrogen (H) is 1 g/mol.
To calculate the molar mass of CH:
Mass of carbon (C) = 12 g/mol
Mass of hydrogen (H) = 1 g/mol
Molar mass of CH = Mass of carbon + Mass of hydrogen
= 12 g/mol + 1 g/mol
= 13 g/mol
Now, we know that the vapour density is given as 39. The vapour density is the ratio of the molar mass of the unknown hydrocarbon to the molar mass of hydrogen gas (H2), which is 2 g/mol.
Vapour density = (Molar mass of hydrocarbon) / (Molar mass of hydrogen gas)
39 = (Molar mass of hydrocarbon) / 2 g/mol
To find the molar mass of the hydrocarbon:
Molar mass of hydrocarbon = Vapour density * Molar mass of hydrogen gas
= 39 * 2 g/mol
= 78 g/mol
So, the molar mass of the hydrocarbon is 78 g/mol.
Now, we divide the molar mass of the hydrocarbon by the molar mass of the empirical formula to find the ratio of the molecular formula to the empirical formula.
Ratio = Molar mass of hydrocarbon / Molar mass of empirical formula
= 78 g/mol / 13 g/mol
= 6
The ratio is 6, which means the molecular formula has six times the number of atoms as the empirical formula.
Finally, to determine the molecular formula, we multiply the empirical formula by the ratio:
Molecular formula = Empirical formula * Ratio
= CH * 6
= C6H6
Therefore, the molecular formula of the hydrocarbon is C6H6.