A hydrogen has an empirical formula CH and a vapour density of 39.Determine its molecular formula,show workings.

C: 12xn

H: 1xn

39=12n+1n
13n=39
n=3
C3H3

To determine the molecular formula from the empirical formula and the vapor density, you need to know the molar mass of the compound. The molar mass gives you the mass of one mole of the substance, which allows you to calculate the ratio between the empirical and the molecular formula.

Step 1: Calculate the molar mass of the empirical formula (CH):
- The molar mass of carbon (C) is 12.01 grams/mole.
- The molar mass of hydrogen (H) is 1.01 grams/mole.
- Multiply the atomic masses by the number of atoms in the empirical formula and sum them:
Molar mass of CH = (12.01 g/mole) + (1.01 g/mole) = 13.02 grams/mole.

Step 2: Calculate the molar mass from the vapor density:
- The vapor density (VD) is the ratio of the mass of a given volume of the gas to the mass of an equal volume of hydrogen gas under the same conditions.
- The molar mass of hydrogen (H2) is 2.02 grams/mole.

Since the empirical formula of the substance is CH (carbon and hydrogen), the molar mass of CH is approximately half of the molar mass of H2.
Molar mass of CH = 2 × Molar mass of hydrogen = (2 × 2.02 g/mole) = 4.04 grams/mole.

Step 3: Calculate the ratio between the empirical and molecular formula:
- Divide the molar mass from the vapor density by the molar mass of the empirical formula:
Ratio = Molar mass from vapor density / Molar mass of empirical formula
Ratio = (39 g/mole) / (4.04 g/mole) ≈ 9.65

Step 4: Determine the molecular formula:
- Multiply the empirical formula by the ratio obtained in Step 3 to get the molecular formula:
Molecular formula = Empirical formula × Ratio
Molecular formula = CH × 9.65 = C9.65H9.65

Therefore, the molecular formula of the compound with the empirical formula CH and a vapor density of 39 is approximately C9.65H9.65.