lesson plan electrolysis with instructional lesson

7/30/2019 Lesson Plan Electrolysis With Instructional Lesson

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LESSON PLAN

Class: Form 2

Subject: Science

Learning Area: Water and solution

Learning Objective : understanding the composition of water.

Date:

Duration: 1 hour 10 minutes

a) Learning outcome :

By the end of the lesson, Students should be able to:

• Determine the composition of water.

• Test the presence of hydrogen and oxygen.

b) High Order thinking:

1)Analyzing:

Use a diagram to show how oxygen and hydrogen released from

water.

Conduct an experiment to test the presence of hydrogen and oxygen.

2) Questioning:

It is really water can extinguished the fire? If no, why?

Water is an electric conductor or not?

Can you use pencil as electrode? Why?



Methodology:-

a) Warm-up activity(Recap):-

Q-What the composition of water?

Q-What is the electrolysis process?

Q-State the ratio between Hydrogen and Oxygen

Q- Which gas is flammable? How about another one?

b) Introduction:-

Today we are going to test the presence of oxygen and hydrogenin water by electrolysis.

c) Explanation:-

Explanation will be done by using diagram about how electrolysis

takes place in order to release hydrogen and oxygen gases.

Explanations include the type of electrodes used and the

relationship between sulfuric acid and the electrical flow.

Demonstration:-

Demonstrate how to carry out the experiment.

d) Evaluation/Assessment:-

Students will be asked during experiment and at the end of the

experiment :

Q-Which side is hydrogen gas and which side is oxygen gas?How do you know?

Q-Which one is cathode and which one is anode? Or which one

positive and which one are negative?

Q-What did you observed after test? What the conclusion?



INSTRUCTIONAL LESSON

ELECTROLYSIS

DEFINITION

• Electrolysis is the passage of an electric current through an ionic

substance that is either molten or dissolved in a suitable solvent,

resulting in chemical reactions at the electrodes and separation of

materials.

MECHANISM OF Electrolysis

The mechanism of electrolysis was first explained by a Swedish scientistArrhenius in 1887.

MAIN FINDING OF THEORY:

1-An electrolyte on dissolving in water dissociates in water into free ions and

allows electric current to pass through it.

http://en.wikipedia.org/wiki/Electric_current

http://en.wikipedia.org/wiki/Ion

http://en.wikipedia.org/wiki/Electric_current

http://en.wikipedia.org/wiki/Ion



2-The degree of dissociation is the extent to which an Electrolyte

dissociates into ions.

3-The ions carry an electric charge and are responsible for the flow of

current through the solution. The amount of electricity conducted by an

Electrolyte depends upon the concentration of ions in the solution.4- The total magnitude of positive charge is equal to the total

magnitude of negative charge in the aqueous solution of electrolyte.

GENERAL TERMS

• Electrolytic cell

is the complete setup or vessel in which electrolysis is carried

out. It has three component parts:

1. an electrolyte

2. two electrodes (a cathode and an anode).3. a battery

2. ELECTROLYTES

1. substance that conducts electric current as a result of a

dissociation into positively and negatively ions in solution or

molten form.

2. Examples:

1. Molten salts

2. Solution of salts in water

3. Solution of acids4. Solutions of alkalis

http://en.wikipedia.org/wiki/Electrolyte

http://en.wikipedia.org/wiki/Cathode

http://en.wikipedia.org/wiki/Anode

http://www.britannica.com/EBchecked/topic/182467/electric-current

http://en.wikipedia.org/wiki/Electrolyte

http://en.wikipedia.org/wiki/Cathode

http://en.wikipedia.org/wiki/Anode

http://www.britannica.com/EBchecked/topic/182467/electric-current



Electrode

is an electrical conductor immersed in the electrolyte by which electriccurrent enters or leaves the electrolyte.

• In an electrolytic cell:

Anode is a Positive electrode

Cathode is a negative electrode

REMEMBER the story of



Some key differences with an electrochemical cell set-up:

• the two half-reactions are not separated by a salt bridge

• an electrochemical cell (or other source of electric current) will be

required.

Other important items to note:

• The anode of the electrolytic cell is the site of oxidation and the

cathode is the site of reduction, just as in an electrochemical cell.

• In an electrochemical cell, the anode is negative and cathode positive,

but this is reversed in the electrolytic cell - the anode is positive and

the cathode is negative.



PROCESS OF ELECTROLYSIS

Electricity be conducted through an electrolytic cell until all of the ions are

used up.

An electrical potential is applied across a pair of electrodes immersed in the

electrolyte.• The externally supplied direct electric current supplies the energy

necessary to create or discharge the ions in the liquid or solution.

• Electric current is carried by electrons in the external circuit.

• Note:

Electrons do not actually pass through the liquid. They appear to

do so.

Battery continuously sends electron down to the cathode and

receives an equal number back from the positive anode

• Each electrode attracts ions that are of the opposite charge.

• Positively charged ions (cations) move towards the electron-providing

(negative) cathode.

• Negatively charged ions (anions) move towards the positive anode.

• Ions that gain or lose electrons to become uncharged atoms separate

from the electrolyte. This is called discharging.

•

EXAMPLE• ELECTROLYSIS OF MOLTEN NaCl

2NaCl(s) → 2Na+(l)

+

Cl-(l)

The half equations are written so that the same number of electrons

occur in each equation.

Sodium metal at the (-)Cathode

2Na+ + 2e- → 2Na

Chlorine gas at the (+)Anode2Cl- - 2e- → Cl2

• The overall reaction is

2Na+Cl-(l) → 2Na(s) + Cl2(g)

SELECTIVE DISCHARGE OF IONS:-

http://en.wikipedia.org/wiki/Electrode

http://en.wikipedia.org/wiki/Electric_charge

http://en.wikipedia.org/wiki/Cation

http://en.wikipedia.org/wiki/Anion

http://en.wikipedia.org/wiki/Electrode

http://en.wikipedia.org/wiki/Electric_charge

http://en.wikipedia.org/wiki/Cation

http://en.wikipedia.org/wiki/Anion



The preferential discharge of ions present in an electrolyte at the respective

electrode is known as SELECTIVE discharge of ions.

Factors affecting the selective discharge of ions:-

1. RELATIVE POSITIONS OF THE ION IN THE METAL ACTIVITY SERIES.2. The concentration of ions in the electrolyte

3. The nature of electrode

• RELATIVE POSITIONS OF THE ION IN THE METAL ACTIVITY SERIES.

Lower the position of the ion in the metal activity series …………….greater the

tendency to be liberated at the respective electrodes

2. The concentration of ions in the electrolyte

Higher the concentration of ions in the electrolyte…………….. Greater the tendency to be discharge

3. The nature of electrode

Nature of electrodes determine the preferential ion, which

will be discharged at the electrode.

Inert electrodes : iron, silver, platinium do not take part in

electrolytic reaction.

Active electrodes : copper, nickel, silver take part in the

electrolysis reaction.

Industrial Application of Electrolysis:-



1- EXTRACTION OF METALS

EXAMPLE = ALUMINIUM METAL)

Electrolysis of molten Alumina

• The electrolyte a solution of alumina in cryolite (Na3AlF6) melts at

about 900 °C

and electrolysis is done at about 950 °C.

• Electrolysis separates the molten ionic compound into its elements.



REACTIONS

• Aluminium metal at the (-)cathode

4Al3+ + 12e-→ 4Al (Reduction)

• Oxygen gas at the (+)anode

6O2- → 3O2 + 12e- (Oxidation)

The overall reaction

2Al2O3(l) → 4Al(l) + 3O2(g)

2-PREPARATION OF ALKALI & CHLORINE GAS

• The NaCl will split into Na+ and Cl- ions

• Water splits into H+ and OH- ions.

– What will happen during electrolysis?

Remember– Na is VERY Reactive, it is much more likely to exist as an ion

than Hydrogen.

• REACTIONS

• At the Cathode

2H+ + 2e- → H2

• At the Anode

2Cl– → Cl2 + 2e–

• The non-permeable ion exchange membrane at the center of the cell

allows the sodium ions (Na+) to pass to the second chamber where

they react with the hydroxide ions to produce caustic soda (NaOH).

• The overall reaction

• 2NaCl + 2H2O → Cl2 + H2 + 2NaOH

3- ELECTROPLATING

http://en.wikipedia.org/wiki/Electron



http://en.wikipedia.org/wiki/Ion_exchange_membrane

http://en.wikipedia.org/wiki/Sodium

http://en.wikipedia.org/wiki/Caustic_soda



http://en.wikipedia.org/wiki/Ion_exchange_membrane

http://en.wikipedia.org/wiki/Sodium

http://en.wikipedia.org/wiki/Caustic_soda



• An electrolytic process of Formation of a thin protective coating of a

non-reactive or superior metal on an article made of a more reactive

or inferior metal.

• PURPOSE

–

To protect the article from rusting – To make the article look better

• Most commonly used metals for electroplating

– Copper, Chromium, Silver, Tin

The anode usually is made of the plating metal. The object to be plated is

the cathode.

Electrolysis with Active Electrodes –

Gold plating

4-ELECTRO REFINING OF METALS

– is a process by which metals containing impurities

are purified by electrolysis to give a pure metal.

• EXAMPLE:-



• ELECTRO REFFINING OF COPPER



REFERENCES

• BOOKS :

1- Chemistry ‘A course for O’level’ by Christopher N. Prescott

2- New edition chemistry by Richard Harwood3- GCSE chemistry by M.J.Denial

4- GCSE chemistry for class X by R D Madan & B.S.Bisht

5- Chemistry for class IX(book I),STBB

• WEBSITES:

www.britannica.com

www.thinkquest.com

www.yteach.com

www.wikipedia.org ------------------------------- The End ----------------------------------

ELECTRO REFINING OF COPPER

ELECTROLYTE Aqueous copper sulphate solution

http://www.britannica.com/

http://www.thinkquest.com/

http://www.yteach.com/

http://www.wikipedia.org/

http://www.britannica.com/

http://www.thinkquest.com/

http://www.yteach.com/

http://www.wikipedia.org/



ELECTRODES CATHODE : pure thin sheet of copperANODE : Impure block of copper

IONS PRESENT CuSO4 → Cu2+ + SO42-

H2O → H+ + OH-

REACTION AT THE CATHODE Cu2+ ions are discharged at the cathode as neutCu2+ + 2e → Cu

REACTION AT THE ANODE Copper anode itself loses electrons to give Cu2+ Cu → Cu2+ + 2e

lesson plan electrolysis with instructional lesson

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