Answer:
a) 17 min
b) 4.2 min
Step-by-step explanation:
The time required can be calculated by:
t = q/i
Where q is the charge, and i is the current. The charge may be calculated by:
q = na*n*F
Where na is the number of moles of the anality, n is the number of moles of electrons, and F is the faraday constant (96485 C/mol).
a) The element will be in the cathode, thus it will reduce:
Co⁺² + 2e⁻ ⇄ Co
The molar mass of Co is 58.93 g/mol, thus:
na = mass/molar mass
na = 0.250/58.93
na = 4.24x10⁻³ mol
n = 2 mol
q = 4.24x10⁻³*2*96485
q = 818.2 C
t = q/i
t = 818.2/0.8
t = 1022.74 s/60
t = 17 min
b) In the anode an oxidation is happening, and n = 2 too. The molar mas of Co3O4 is 240.8 g/mol, thus:
na = 0.250/240.8
na = 1.04x10⁻³ mol
q = 1.04x10⁻³*2*96485
q = 200.3 C
t = 200.3/0.800
t = 250.43 min/60
t = 4.2 min