Question

A sample of ethane(C2H6) gas has the same mass as 1.5 10^20 molecules of methane CH4. how many C2H6 molecules does the sample of gas contain?

Answer 1

(Avogadro's number)
6.02 x 10∧23 molecules of methane = 1 mole
∴ 1.5 x 10∧20 molecules of methane = (1.5 x 10∧20 x 1) ÷ (6.02 x 10∧23) moles
                                                                 = 2.49 x 10∧ -4 moles

Molar mass of Methane (CH4) = 12 + 1x4 =  16 g
Mass of methane = molar mass x no. of moles = 16 x 2.49 x 10∧ -4 = 3.984 x 10∧-3 g (This is the same mass as Ethane)

Ethane (C2H6) = 12x2 + 1x6 = 30

If 30 g of Ethane has 6.02 x 10∧23 molecules
∴3.984 x 10 ∧-3 g = (3.984 x 10∧-3 x 6.02 x 10∧23) ÷ 30
                                 = 8 x 10∧19 molecules of Ethane

Answer 2

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