Phenol is treated first with concentrated sulphuric acid to give phenol-2,4-disulphonic acid, which is then treated with concentrated nitric acid to give 2,4,6-trinitrophenol (picric acid). What mass of picric acid is obtained from 9.4 g of phenol, assuming complete conversion? (Atomic masses: H = 1, C = 12, N = 14, O = 16)
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 22.9 g
In both steps the ring and the –OH group of phenol are kept, so one molecule of phenol gives one molecule of 2,4,6-trinitrophenol:
\( \displaystyle \ce{C6H5OH + 2H2SO4 -> C6H3(OH)(SO3H)2 + 2H2O} \)
\( \displaystyle \ce{C6H3(OH)(SO3H)2 + 3HNO3 -> C6H2(OH)(NO2)3 + 2H2SO4 + H2O} \)
So the moles of picric acid are equal to the moles of phenol.
\( \displaystyle n(\ce{C6H5OH}) = \frac{9.4\ \mathrm{g}}{94\ \mathrm{g\ mol^{-1}}} = 0.100\ \mathrm{mol} \)
\( \displaystyle M(\ce{C6H3N3O7}) = 6 \times 12 + 3 \times 1 + 3 \times 14 + 7 \times 16 = 229\ \mathrm{g\ mol^{-1}} \)
\( \displaystyle m(\text{picric acid}) = 0.100\ \mathrm{mol} \times 229\ \mathrm{g\ mol^{-1}} = 22.9\ \mathrm{g} \)