Question

What will be the mol fractionon of ethanol in a sample of sulphuric acid containing 85% ethanol by mass

Answer 1

Let weight of solution is 100g

∵ mass % of ethanol is 92 %

∴ mass of ethanol in solution = 92g

and mass of water = 100 - 92 = 8g

Now, mole fraction of ethanol = mole of ethanol /(mole of ethanol + mole of water )

Mole of ethanol = mass of ethanol/molar mass of ethanol

= 92/46 = 2 [ ∵ molar mass of ethanol (C₂H₅OH) is 46 g/mol ]

Mole of water = mass of water/molar mass of water

= 8/18 = 4/9 = 0.444

∴mole fraction of ethanol = 2/(2 + 0.444) = 2/2.444 = 0.818

Hope it helped