JAMB Free Tutorial on Electrolysis [Chemistry Tutorial]



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JAMB Free Tutorial on Electrolysis [Chemistry Tutorial]

Today on our JAMB Free Tutorial, we will focus on CHEMISTRY. We will treat Electrolysis. At the end of the tutorial, we will also ask 9 objective questions and the first person to answer all the questions correctly will win N2,000. The money will be transferred to the person’s account. That’s amazing right? See the tutorial below.

We have said everything above! Today, our topics is ELECTROLYSIS. You can check the table of content (content in post) below to scan through the sub-topics we will teach.

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ELECTROLYSIS

Is the chemical decomposition of a substance in its molten state or molten form when electric current is passed through it.

TERMS USED IN DESCRIBING ELECTROLYSIS

  1. Electrolyte:

An electrolyte is a substance that contains mobile ions and undergoes decomposition when electric current is passed through it. The substance or compound must be in a liquid form. Either as aqueous solution or molten state of the compound.

  1. Non – Electrolyte:

They are substances or compound that do not contain mobile ions and not decomposed when electricity is passed through it. In other words, they do not conduct electricity.

ElectrolyteNon – Electrolyte
(Tartaric acid) Grape juiceBenzene
Dilute H2SO4Kerosene
MilkNaOH (pallet)
NaCl (aq)Ethanol
Ethanoic acidEther
 Butanol

Notes:

  1. Ethanoic acid is a weak electrolyte. Only little molecules ionizes.
  2. Electrolyte conduct electricity because they can ionize while non – electrolyte do not because of their inability to ionize.
  3. All salts, acids and alkalis provided they are in their molten state or solution form are electrolytes.

(3) Electrodes:

These are rods, wires or plates through which current enters or leaves the electrolyte. (All are conductors).

  1. Anode: It is the positive electrode through which electron leaves the electrolyte or conventional current enters the electrolyte.
  2. Cathode: It is the negative electrode through which electron enters the electrolyte or conventional current leaves the electrolyte.

Refer to your textbook for diagram of a simple electrolyte cell and positions of ions in electrochemical series

FACTORS AFFECTING THE SELECTIVE DISCHARGING IONS IN SOLUTION:

  • Positions of ions in ECS (Electrochemical Series).
  • Concentrations if ions in solution.
  • Nature of electrode.

Positions of Ions in ECS:

If all factors are constant, a cation that is more electropositive or an anion that is more electronegative is always discharged in preference to the less electropositive or electronegative ions respectively.

Concentration of Ions in Solution:

For concentration to affect competing ions in solution, the competing ions must be closely placed in the ecs. Or else the effect of concentration is void. However, if the effect is valid, the ions with high concentration is discharged.

Nature of Electrode:

Sodium (Na) has strong affinity for mercury forming Na/Hg (sodium amalgam) and it requires less energy to discharge when using mercury electrode.

Two inert electrodes are platinum and carbon or graphite unless platinum comes in contact with chlorine and carbon comes in contact with oxygen. I.e. carbon or graphite electrode attacks and liberates oxygen. Platinum is attacked by liberated chlorine.

Check more

FARADAY’S FIRST LAW OF ELECTROLYSIS

It states that the mass of a substance deposited during electrolysis is directly proportional to the quantity of electricity passing through it.

M Q
Q = It
M = ZQ
Z = Electrochemical equivalent
Q = Charge
Also = Density = Mass/Volume
but Volume = Thickness * Area

From first formulae
M = ZIt
Cross multiply = DAL = M = Zit
DAL = Zit
L =  (in case you’re asked to find V, thickness & Area).

FARADAY’S SECOND LAW OF ELECTROLYSIS

It states that when the same quantity of electricity is passed through different electrolytes, the relative number of moles of elements discharged are inversely proportional to the charges on the ions of the element.

PLEASE TAKE NOTE OF THE FOLLOWING

  • 1F ⟶ 1e
  • F = 96500
  • The electron (e) is determined by the charge of the element.
  • Oxygen has a constant electron i.e 4. It can be proven with the below equation:
    4OH ⟶ 2H2O + O+ 4e
  • Also remember oxygen possess a charge of -2, its occurance multiplied by its charge = -2  2 = 4e.
  • When using cross multiply formulae,
    Molar mass ⟶ number of electrons  Faraday
  • Mass ⟶ quantity of electricity.

Application of Electrolysis

  1. It is used for the purification of metals like copper, gold e.g. during purification, the metal to be purified is made the anode while the pure metal is made the cathode.
  2. It is used for electroplating (covering a metal with another metal). During electroplating, the metal to be electroplated is the cathode while the metal that is used for electroplating is made the anode. High current is needed for electroplating.
  3. It is used for the preparing of certain compound like NaOH. It is used for extracting very reactive metals like Na, Ca, Mg, Al etc.
  4. Note: As you’re going down the ecs, the reactivity of metals decreases and their positivity too.

EXAMPLE

  • How long would it take to deposit 0.08g of copper CuCl2 solution by passing a current of 0.5A?

Solution

NB: Click on image for better view.

EXERCISES

The first person to answer the 9 questions correctly will be rewarded with N1,500. We did it on our first CHEMISTRY TUTORIAL AND BIOLOGY TUTORIAL and we will do it again! Use the comment box below to tell us your answer.

1. The commonest feature of reactions at the anode is that
A electrode dissolves
B electrons are consumed
C oxidation is involved
D ions are reduced

2. In the electrolysis of a concentrated solution of sodium chloride using inert electrodes,which of the following ions are discharged at the cathode and anode respectively?
A H+ and Cl-
B H+ and OH-
C Na+ and OH –
D Na+ and Cl-

3 which of the following is an electrolyte?
A mercury
B alcohol
C sodium acetate solution
D solid potassium hydroxide

4. A concentrated solution containing H+,Cu+,OH-,Cl- was electrolysed using platinum electrodes. The ion that will be discharged at the cathode is
A OH-
B Cl-
C Cu+
D H+

5. In the electrolysis of CuSO4 using plantinum electrodes,the reaction at the anode is
A 2OH- + 2OH- ___ 2H2O + O2
B 4H+ + 4e __2H2
C 4OH- _ 4e __2H2O + O2
D. 2OH _ 2e __2OH

6. What current will deposit 3.25g of zinc in 2hours?
A 3.25A
B 2.00 A
C 1.34A
D. 0.67A

7. Calculate the volume in cm3 of oxygen evolved at s.t.p when a current of 5A is passed through acidified water for 193s
A 0.224
B 56.000
C 224.000
D 0.056 ( F=96500Cmol^-1, molar volume of a gas at stp = 22.4dm3)

8. In an electrochemical cell, polarization is caused by
A tetraoxosulphate(vi) acid
B hydrogen
C chlorine
D oxygen

9. Hydrogen can be diplaced by
A Cu
B Au
C Hg
D Al

Please use the comment box below to drop your answers.

Credit: This CHEMISTRY tutorial was prepared by Ejimgini, Ozioma Promise a Biology/Chemistry Tutor.

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