Question

cyclopentane, a hydrocarbon with carbon and hydrogen , has a molar mass of 70.13 g/mol. If the combustion of .5600 g of cyclopentane produces .7195 grams h20 and 1.757 grams CO2 what is the molecular formula?

Answer 1

let in compound number of moles of C and H be x and y respectively

Number of moles of CO2 = mass of CO2 / molar mass CO2

= 1.757/44

= 0.0399

Number of moles of H2O = mass of H2O / molar mass H2O

= 0.7195/18

= 0.04

Since 1 mol of CO2 has 1 mol of C

Number of moles of C in CO2= 0.0399

so, x = 0.0399

Since 1 mol of H2O has 2 mol of H

Number of moles of H = 2*0.04 = 0.0799

Divide by smallest to get simplest whole number ratio:

C: 0.0399/0.0399 = 1

H: 0.0799/0.0399 = 2

So empirical formula is:CH₂

Molar mass of CH2 = 1*MM(C) + 2*MM(H)

= 1*12.01 + 2*1.008

= 14.026 g/mol

Now we have:

Molar mass = 70.13 g/mol

Empirical formula mass = 14.026 g/mol

Multiplying factor = molar mass / empirical formula mass

= 70.13/14.026

= 5

So molecular formula is:C₅H₁₀

Answer: So molecular formula is:C₅H₁₀