Chemistry - Complete P-block Question with Solution | TestHub
Aqua regia (3 volumes conc. HCl + 1 volume conc. HNO₃) dissolves gold, producing chloroauric acid and evolving a colourless gas (G). A jeweller dissolves 9.85 g of pure gold in excess aqua regia.
If x = mass (in g) of chloroauric acid formed and y = volume (in mL) of (G) evolved, measured at 1 atm and 0 °C, find the value of (x + y). [H = 1, N = 14, O = 16, Cl = 35.5, Au = 197]
Answer:
Solution:
In aqua regia the oxidant is HNO₃, reduced to the colourless gas NO, so (G) = NO; gold is oxidised to Au(III) and chloroauric acid is H[AuCl₄]. Balanced dissolution : Au + HNO₃ + 4HCl → HAuCl₄ + NO↑ + 2H₂O (Au : 0 → +3 loses 3 e⁻ ; N : +5 → +2 gains 3 e⁻, hence Au : NO = 1 : 1). n(Au) = 9.85/197 = 0.05 mol. x : n(HAuCl₄) = 0.05 mol, M = 1 + 197 + 4 × 35.5 = 340 g/mol → x = 0.05 × 340 = 17 g. y : n(NO) = 0.05 mol → y = 0.05 × 22400 = 1120 mL. x + y = 17 + 1120 = 1137.
