Question

if all ethene molecules are replaced by same number of molecules of ethyne, then molar mass of the gaseous mixture will be

Answer 1

A/C to question,
all ethene molecules are replaced by same number of molecules of ethyne .
Let assume number of molecules each of them = x
Then, number of moles of ethene are replaced by ethyne = x/Nₐ
Here, Nₐ is Avogadro's number .

∴ molar mass of mixture = (n₁M₁ + n₂M₂)/(n₁ + n₂)
Where n₁ is the number of mole of ethene
n₂ is the number of mole of ethyne
M₁ is the molar mass of ethene
M₂ is the molar mass of ethyne.
Here , n₁ = n₂ = x/Nₐ
M₁ = 28 g/mol [ because molecular formula is C₂H₄]
M₂ = 26 g/mol [ because molecular formula is C₂H₂]

Now, molar mass of mixture = (x/Nₐ × 28 + x/Nₐ × 26)/(2x/Nₐ)
= (28 + 26)/2 = 27 g/mol

Hence, answer is 27g/mol