Peka - Chemistry Form 4 - Student\'s and Teacher\'s Manual - 01

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Peka - Chemistry Form 4 - Student's and Teacher's Manual - 01 - Electrochemistry - Free download as PDF File (.pdf), Tex...

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STUDENT’S MANUAL

PEKA CHEMISTRY FORM 4 YEAR ………. SMK KAI CHUNG NAME

: …………………………….

CLASS

: ………………..

PRACTICAL ASSIGNMENT I Theme Learning Area Learning Objective Peka I Problem

: Interaction between chemicals : Electrochemistry : Analysing the electrolysis of aqueous solutions : To investigate the effect of specific electrodes on the electrolytic process of an electrolysis. : How do the types of electrodes affect the products of electrolysis of copper (II) sulphate solution?

Element Assessed : C I C II C III C IV CV Instructions

-

Skills in planning an experiment Skills in carrying out an experiment Skills in collecting or recording data Skills in interpreting data and making conclusion Scientific attitudes and noble values

: i) Students are required to plan, design and conduct an experiment on the electrolysis of copper(II) sulphate by using copper electrodes and carbon electrodes. ii) Your report should include the following criteria : 1. Aim/Problem statement 2. Hypothesis 3. Variables 4. Apparatus/Materials 5. Methods/Steps/Procedures 6. Table of results/Observation 7. Analysis/Discussion 8. Conclusion

Date to conduct experiment

:

Date to hand in report

:

TEACHER’S MANUAL

Title

: The effect of the types of electrodes on the selective discharge of ions at the anode and cathode

Aim

: To investigate the effect of specific electrodes on the electrolytic process of an electrolysis

Problem statement : How do the types of electrodes affect the products of electrolysis of copper (II) sulphate solution? Hypothesis

: Different types of electrodes will form different products at the electrodes.

Variables : Manipulated Responding Fixed

: Type of electrodes. : Products at the anode. : Volume and concentration of copper(II) sulphate solution.

Materials

: 1 mol dm-3 copper(II) sulphate, CuSO4 solution.

Apparatus

: Electrolytic cells, carbon electrodes, copper electrodes, ammeter, connecting wires with crocodile clips, power pack/batteries, wooden splinter and electronic balance.

Procedure

:

1. The carbon electrodes are cleaned with a piece of sandpaper. 2. The carbon electrodes are weighed individually and the readings are recorded. 3. An electrolytic cell is set up as shown in the diagram. 4. The cell is filled up with copper(II) sulphate solution until its level is above the electrodes . 5. The electric current is allowed to flow for 15 minutes. 6. Changes at both electrodes are noted and recorded. 7. The gas collected is tested with a glowing wooden splinter. 8. The anode is taken out, washed, dried and then weighed using an electronic balance. 9. The experiment is repeated using copper electrodes. 10. All the readings and observations are recorded in the table below. Observation :

Observation

Inference

Mass of the anode (g)

Electrode Cathode a) A brown metallic substance is deposited at the cathode. Carbon

b) The blue colour of electrolyte become lighter. a) A brown metallic substance is deposited at the cathode.

Copper

b) The blue colour of electrolyte remains unchanged.

Anode a) A gas is liberated. b) The gas ignites a glowing splinter.

a) The electrode becomes thinner.

Cathode

Anode

Before

After

The metallic deposit at the cathode is copper.

The gas liberated at the anode is oxygen.

3.09

3.09

Copper is The copper deposited at anode the cathode. corroded.

0.77

0.74

Discussion : A) Using Carbon as Electrodes 1. The ions present in copper(ll) sulphate solution are H+ , OH- , Cu2+ and SO42-. 2. At the anode a) OH- ions and SO42- are attracted to the anode but only OH- is selectively discharged. b) This is because OH- occupies a lower position than SO42- in the electrochemical series. c) The discharge of OH- will produce oxygen according to the following equation. 4OH- → 2H2O + O2 + 4e d) Thus, oxygen is liberated at the anode . It will ignite a glowing splinter. 3. At the cathode: a) H+ and Cu2+ are attracted to the cathode but only Cu2+ is chosen to be discharged by the carbon electrode. b) The discharge of Cu2+ will produce copper, Cu. Cu2+ + 2e → Cu c) Thus, copper is formed and deposited on the cathode. d) As the experiment continues, more and more copper ions will be discharged. The Cu2+ ions give copper(II) sulphate its blue colour. Thus, as times continues, the solution will become less bluish because concentration of the copper ions decreases. B) Using Copper as Electrodes 1. The sulphate ions and hydroxide ions move to the anode. However, these ions are not discharged. Instead, the copper in the copper anode ionises to form copper ions Cu2+. Cu→ Cu2+ + 2e 2. During the electrolysis using copper electrodes, the copper (II) ions and hydrogen ion move to the cathode. Copper(II) ion is lower than hydrogen in the electrochemical series. Hence, in these copper ions are selectively discharged to form copper metal. Cu2+ + 2e → Cu 3. The intensity of blue colour of the electrolyte remains unchanged. This is because the concentrated of the blue copper(II) ions remains unchanged. For one copper(II) ion discharge to form a copper atom at the anode, one copper atom from the anode will dissolve to form a copper (II) ion. Conclusion : Different type of electrode used, can affect the products of electrolysis. The hypothesis is accepted.

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