Lesson Notes By Weeks and Term - Senior Secondary 2

TERM׃ 3^RD TERM

WEEK SEVEN

Class: Senior Secondary School 2

Age: 16 years

Duration: 40 minutes of 5 periods each

Date:

Subject: Chemistry

Topic:- Electrolysis 2

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

1. State faradays laws of Electrolysis
2. Carry out calculations using faradays laws of Electrolysis
3. Identify the uses of Electrolysis

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers,

demonstration, videos from source

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

PRESENTATION	TEACHER’S ACTIVITY	STUDENT’S ACTIVITY
STEP 1 INTRODUCTION	The teacher reviews the laws of Electrolysis to the students.	Students pay attention
STEP 2 EXPLANATION	Teacher carry out calculations involving laws of Electrolysis and also aid students to do same.	Students pay attention and participate
STEP 3 DEMONSTRATIO N	Teacher discusses the uses of Electrolysis .	Students pay attention and participate
STEP 4 NOTE TAKING	The teacher writes a summarized note on the board	The students copy the note in their books

 

NOTE

ELECTROLYSIS 2

Faradays laws of electricity

Faraday's First Law of Electromagnetic Induction states that a change in magnetic field within a closed loop induces an electromotive force (EMF) in the loop. This induced EMF creates an electric current if the circuit is closed.

From the definition, we get

           m is proportional to Q

        Q = I x t

The first law of electrolysis can also be stated as follows; the mass of the element discharged during an electrolysis is directly proportional to,

1. The magnitude of the current, and
2. The time of flow of the current

        Hence, m is directly proportional to I x t

                 m = EIt

Where E is a constant.

Faraday's Second Law quantifies the induced EMF, stating that it is directly proportional to the rate of change of magnetic flux through the loop. Mathematically, it can be expressed as EMF = -dΦ/dt, where EMF is the induced electromotive force, dΦ/dt is the rate of change of magnetic flux, and the negative sign indicates the direction of the induced current according to Lenz's law.

Calculations involving Electrolysis

Example 1; Calculate the mass of silver deposited when a current of 2.6A is passed through a solution of a silver salt for 70minutes. (Ag = 108, 1faraday = 96 500C )

Solution.

Quantity of electricity used = It = (2.6 x 70 x 60) C

Ag⁺_(aq)  + e^- forward arrow Ag(s)

108g.         1F.                     108g

96500 C liberate108g of Ag1

(2.6 x 70 x 60) C will liberate 2.6 x 70 x 60 x 108

                                                     96500              = 12.22g

Therefore the mass of silver deposited is 12.22g.

Example 2. Calculate the volume of oxygen evolved at 285 K and 0.9 x 10⁵Nm-2 when a current of 2.5 A is passed through acidified water for 1.5 min. (Molar volume of a gas is 22.4dm³, standard pressure = 1.01 x 10⁵Nm-²,

1faraday = 96500C)

Solution

Quantity of current used = I t = ( 2.5 x 1.5 x 60) C

4OH- _(aq) forward arrow 2H2O(l) + O₂(g) + 4e-

                                                           22.4dm³.   4F

4 x 96500C of electricity liberate 22.4 dm³ oxygen at stp.

Thus 2.5 x 1.5 x 60 x 22.4. dm³

                 4 x 96500

=  2.5 x 1.5 x 60 x 22400 cm³

              4 x 96500

=  13.06cm³ at stp.

Now convert the volume at STP to it's volume at 285K and 0.91 x 10⁵ Nm-²

p1V1 = p2V2

   T1.        T2

Where p1 = STP = 1.01 x 10⁵Nm-²

             V1 = 13.06cm³

            T1 = 273K

             p2. = 0.91 x 10⁵ Nm-²

             T2 = 285K

V2 = p1V1T2

             T1

= 1.01 x 10⁵ x13.06 x 285 cm³

        0.91 x 10⁵ x 273

= 15.13cm³.

The volume of oxygen evolved at 0.91 x 10⁵Nm-² and 285K is 15.13cm³.

Uses of Electrolysis

Electrolysis, the process of using an electric current to drive a non-spontaneous chemical reaction, has various practical applications:

1. Metal Production: Electrolysis is crucial in extracting reactive metals like aluminum and sodium from their ores. The Hall-Héroult process is used for aluminum extraction, while sodium is produced through the Downs cell.
2. Electroplating: Electrolysis is employed in electroplating to coat surfaces of objects with a thin layer of metal, enhancing their appearance, corrosion resistance, or conductivity.
3. Water Electrolysis: Electrolysis of water produces hydrogen and oxygen gases. This is significant for hydrogen production, which has potential applications in fuel cells and clean energy technologies.
4. Electrolytic Cells in Batteries: Some batteries, like rechargeable batteries, utilize electrolytic cells to facilitate chemical reactions that store and release electrical energy.
5. Electrolytic Capacitors: Electrolysis is involved in the construction of electrolytic capacitors, which are widely used in electronic circuits for energy storage.

EVALUATION:   1. State faraday’s first law of electrolysis.

2. If a current of 2.5 amperes is passed through a molten sample of aluminum oxide (Al₂O₃) for 30 minutes, calculate the amount of aluminum (in grams) deposited at the cathode. (Assume 100% efficiency)
3. Identify three uses of Electrolysis.

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively