On heating with concentrated sulphuric acid at 413 K, ethanol gives ethoxyethane. What mass of ethoxyethane is obtained from 23 g of ethanol, assuming that all the ethanol is converted into ethoxyethane? (Atomic masses: H = 1, C = 12, O = 16)
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 18.5 g
In the acid-catalysed dehydration of ethanol to an ether, two molecules of ethanol join and lose one molecule of water:
\( \displaystyle \ce{2C2H5OH} \xrightarrow[\text{413 K}]{\ce{H2SO4}} \ce{C2H5OC2H5 + H2O} \)
So the moles of ethoxyethane are half the moles of ethanol.
\( \displaystyle n(\ce{C2H5OH}) = \frac{23\ \mathrm{g}}{46\ \mathrm{g\ mol^{-1}}} = 0.500\ \mathrm{mol} \)
\( \displaystyle n(\ce{C2H5OC2H5}) = \frac{0.500}{2} = 0.250\ \mathrm{mol} \)
\( \displaystyle m(\ce{C2H5OC2H5}) = 0.250\ \mathrm{mol} \times 74\ \mathrm{g\ mol^{-1}} = 18.5\ \mathrm{g} \)
The masses balance: 18.5 g of ethoxyethane and 4.5 g of water (0.250 mol × 18 g mol−1) add up to the 23 g of ethanol taken.