Calculate the oxidation number of chromium in an unknown salt if the electrolysis of the salt yields 9.71g of chromium at the cathode after a current of 10A is passed through a cell for 1.5 hours.the relative atomic mass of chromium is 52.
Current, I = 10 A
Time, t = 1.5 hrs = 90 min = 5400 s
Quantity of electricity, Q = I × t = (10 A) × (5400 s) = 54000 C
Mass of chromium (Cr), m = 9.71 g
Molar mass of chromium (Cr), M = 52 g/mol
Faraday's 1st law can be used.
Faraday's 1st law can be expressed as:
m = (Q × M) / (Z × F)
m = mass of material (g)
M = molar mass of material (g/mol)
Q = quantity of electricity (C)
Z = number of electrons
F = Faraday constant, 96485 (C mol-1)
Z = (Q × M) / (m × F)
Z = (54000 C × 52 g/mol) / (9.71 g × 96485 C mol-1) = 2.997 = 3
Z = 3
Therefore, the oxidation number of chromium in an unknown salt is +3.
Answer: The oxidation number of chromium (Cr) in an unknown salt is +3.