Question

A compound of molar mass 213 contains only carbon, hydrogen, iodine, and oxygen. Analysis shows that a sample of the compound contains 6 times as much carbon as hydrogen, by mass.Calculate the molecular formula of the compound. Express your answer as a chemical formula. Enter the elements in the order: C, H, O, I.

Answer 1

The atomic mass of Iodine = 127 g/mol

Twice the atomic mass = 254

Since the molar mass of the compound is only 213, the comound cannot have more than one Iodine atom

Therfore the number of iodine atom is = 1

Molar mass - Atomic mass of Iodine = 213 - 127 = 86

Suppose there is one atom of Oxygen in the molecule

The mass due to C and H = 86 - atomic mass of oxygen = 86 -16 = 70

If we apportion this in the ratio 6:1 we get 60:10

This corresponds to 5 C atoms (5x12) and 10 H atoms (10 x1)

Hence, the molecular formula of the compound is C₅H₁₀OI

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To write the Chemical formula let us first calculate the Hydrogen Deiciency Index (HDI) of the compound

The molecular formula of the saturated compound with 5 C atom is C₅ H₁₂

In C₅H₁₀OI, O atom is ignored and I atom is treated as H in the calculation of HDI

Therefore HDI = [12- (10+1) ] = 1/2

HID for neutral molecules MUST be an integer (i.e. 0, 1, 2 etc.).

Therefore the molecular formula C₅H₁₀OI does not represent any neutral compound