Electric current in the electrolytes
1.Describe the electric current in electrolytes!
Solution:
Electrolytes are substances whose solutions or melts conduct electric current by means of ions. Electric current in electrolytes is an ordered movement of cations (+) and anions (-). Cations move toward the cathode (-), anions toward the anode (+). Electrolytic dissociation is the process in which neutral molecules of an electrolyte split into ions. Electrolysis is the process during which chemical changes occur at the electrodes and in the electrolyte when electric current passes through it.
2.Calculate:
- a.) the amount of aluminum that is deposited at the electrode during electrolysis in 24 hours by a current of 10 kA. A(Al3+) = 0.093·10-6 kg·C-1
- b.) what current would deposit chromium with a mass of 3.24 g from the electrolyte in 1 hour. A(Cr3+) = 0.18·10-6 kg·C-1
Solution:
- a.) 80 kg of aluminum is deposited at the electrode.
- b.) Chromium is deposited at the electrode by a current of 5 A.
3.Determine the electrochemical equivalent of aluminum and copper
Solution:
The electrochemical equivalents are A(Al)= 0.0932·10-6 kg·C-1 and A(Cu)=0.329·10-6 kg·C-1
4.An electric current of 1 A passes through an electrolyte of CuSO4. How many copper atoms are deposited on the cathode in 10 seconds? A(Cu) = 0.329·10-6 kg·C-1, NA = 6.022·1023 mol-1, Mm = 63.548·10-6 kg·mol-1
Solution:
Analysis:
I = 1 A, t = 10 s, A(Cu) = 0.329·10-6 kg·C-1, NA = 6.022·1023 mol-1, Mm = 63.548·10-6 kg·mol-1
The number of copper atoms deposited on the cathode is N = 3.12·1019 atoms of copper.
5.A sphere with radius r = 5 cm is to be nickel-plated with a layer thickness h = 0.15 mm. How long should the sphere remain in the electrolyte at a current I = 1 A?
Solution:
Analysis:
r = 5 cm = 5·10-2 m, h = 0.15·10-3 m, I = 1 A, A(Ni) = 0.304·10-6 kg·C-1, ρ(Ni) = 8.8·103 kg·m-3
Nickel-plating the sphere takes about 38 hours.
6.Nickel-plating of a metal plate with surface area 100 cm2 took four hours at a current of 0.4 A. Calculate the thickness of the nickel layer formed on the plate!
Solution:
Analysis:
S = 100 cm2 = 10-2 m2, I = 0.4 A, t = 4 h = 14 400 s, v = 2, F = 96.5·103 C·mol-1,
Mm(Ni) = 58.7·10-3 kg·mol-1, ρ(Ni) = 8.9·103 kg·m-3
The thickness of the nickel layer is h = 19.68 μm.
7.How much energy do we need to obtain 1 g of copper by electrolysis of copper sulfate CuSO4, if the electrolysis runs at a voltage of 4 V?
Solution:
Analysis:
m = 1 g = 10-3 kg, U = 4 V, A(Cu) = 0.329·10-6 kg·C-1
During electrolysis we consume 12.2 kJ of energy.
8.Two electrolytic cells with solutions of AgNO3 and CuSO4 are connected in series. How much copper is deposited in the time during which 850 mg of silver is deposited?
Solution:
Analysis:
A(Ag) = 1.118·10-6 kg·C-1, A(Cu) = 0.329·10-6 kg·C-1, mAg = 850 mg. mCu = ?
250 mg of copper is deposited.
9.What electric current passed through the electrolyte if the copper cathode weighed 35 g before the measurement and 39 g after the measurement, which lasted 40 minutes?
Solution:
Analysis:
Δm = 4 g = 4·10-3 kg, t = 40 min = 2400 s, A(Cu) = 0.329·10-6 kg·C-1
The current through the electrolyte was I = 5.065 A.
10.The decomposition voltage during electrolysis of sulfuric acid was 2.2 V. At a voltage of 3.5 V, a current of 2.8 A passed through the electrolyte. The electrodes were 4 cm apart and the cross-sectional area of the electrolytic conductor was 30 cm2. Determine the resistivity of the electrolyte!
Solution:
Analysis:
Ur = 2.2 V, U = 3.5 V, I = 2.8 A, S = 30·10-4 m2, l = 4 cm = 4·10-2 m, ρ = ?
The resistivity of the electrolyte is ρ = 0.0348 m·Ω.