0.070g of hydride of carbon occupies 56cm^3 at s. t.p when vaporized and contained 14.29% by mass of hydrogen. what is the formula for the hydrocarbon

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.

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