Answer:
C₂H₄
Step-by-step explanation:
Assume that you have 100 g of the compound.
Then you have 85.71 g of C and 14.29 g of H.
1. Calculate the moles of each element.
Moles of C = 85.71 × 1/12.01 = 7.130 mol C
Moles of H = 14.29 × 1/1.008 = 14.18 mol H
2. Calculate the molar ratios.
Divide all values by the smallest number.
C: 7.130/7.130 = 1
H: 14.18/7.130 = 1.986
3. Determine the empirical formula
Round off all numbers to the closest integer.
C: 1
H: 2
The empirical formula (EF) is CH₂.
4. Calculate the EF mass
EF Mass = (12.01 + 2.016) u
EF Mass = 14.03 u
5. Calculate the moles of compound
STP is 0 °C and 1 bar.
1 mol of a gas occupies 22.71 dm³ at STP.
56 cm³ = 0.056 dm³ Convert to moles
= 0.056 × 1/22.71
= 2.47 × 10⁻³ mol
6. Calculate the molar mass
MM = mass/moles
= 0.070 g/2.47 × 10⁻³ mol
= 28.39 g/mol
7. Calculate the molecular formula (MF)
The molecular formula is an integral multiple of the empirical formula.
MF = (EF)ₙ
n = MF Mass/EF Mass
= 28.39 u/14.03 u
= 2.023
≈ 2
MF = (CH₂)₂
= C₂H₄
The molecular formula is C₂H₄.
