Question

What is the molecular formula of a compound containing only carbon and hy drogen if combustion of 1.05g of the compound produces 3.30g CO₂ and 1.35g H₂O and its molar mass is about 70g?
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Answer 1

Answer:

A compound containing only carbon and hydrogen produces 3.30g CO₂ and 1.35g H₂O on combustion of 1.05g and has a molar mass of 70g.  Then its molecular formula is C₅H₁₀.

Explanation:

Given that,

         mass of compound = 1.05g

molar mass of compound = 70g

                    mass of CO₂ = 3.30g

                    mass of H₂O = 1.35g

we know that,

      number of moles = mass / molar mass

then,

           moles of CO₂ = 3.3 / 44 = 0.075 mol.

ie, it contains 0.075 moles of C.

          moles of H₂O = 1.35g / 18gmol⁻¹ = 0.075 mol.

ie, it contains 2×0.075 moles of H.

then, ratio C : H = 0.075 : 0.15

⇒                         = 0.075/0.075 : 0.15/0.075

⇒                         = 1 : 2

Empirical formula is CH₂

Empirical formula mass = 14g

       Molecular Formula= n × Empirical formula

        n = molar mass / empirical formula mass

⇒         = 70g / 14g = 5

then, molecular formula = C₅H₁₀

Answer 2

Answer:

C5H10

Explanation: