Chemistry PEKA Mark Scheme 6.1 - Electrochemistry

Mark Scheme PEKA Chemistry Form 4 Experiment No : ......6.1............ Topic: Electrochemistry Aim To investigate the effect of the position of ions in the electrochemical series on selective discharge of  ions at the electrodes

Problem statement

Does the position of ions in the electrochemical series affect the selective discharge of  ions at electrodes? [ K1PP1(i) - Able to write the aim or problem statement correctly]

Hypothesis

The lower the position of ions in the electrochemical series, the higher is the tendency for the ions to be discharged.

Variables

Manipulate Manipulated d variable variable : Position Position of ions in in the electro electrochemica chemicall series series Responding Responding variable variable : Ion discharged discharged at the electrode electrode Fixed variables : Concentration of electrolyte, types of electrode, duration of  electrolysis [ K1PP1(ii) - Able to write the hypothesis or variables correctly]

Materials

0.5 mol dm-3 sodium nitrate solution, 0.5 mol dm-3 copper(II) nitrate solution, 0.5 mol dm-3 sodium sulphate solution

Apparatus

 batteries, carbon electrodes, connecting wires, ammeter, electrolytic cell, test tubes, wooden splinter, matches to list list all the materials and apparatus correctly] [ K1PP1(iii) - Able to

Procedure

1. 2. 3. 4. 5. 6.

Electrolytic cell is filled with 0.5 mol dm-3 sodium nitrate solution until it is half full. The The swi switc tch h is is tur turne ned d on. on. Observ Observati ations ons are are made made at anode anode and and cathode cathode.. Any gas gas produce produced d is tested tested by usin using g a splinte splinter. r. Obse Observ rvat atio ions ns are are recor recorded ded.. Steps 1 to 4 are repeated repeated by replacin replacing g sodium nitrate nitrate solution solution with with copper(II) copper(II) nitrate nitrate solution and sodium sulphate solution.

[ K1PP1(iv) - Able to write the procedure correctly]

Observation

Electrolyte

Sodium nitrate

Ions present in electrolyte Na+, NO3 -, H+, OH-

Copper(II) ni nitrate

Cu2+, NO3-, H+, OH-

Sodium sulphate

Na+, SO42- , H+, OH-

Observation Anode Cathode Gas bubbles are Gas bubbles are released. released. A colourless gas A colourless gas relight a glowing  produces ‘pop’ splinter. sound wgen tested with splinter. Gas bubbles are A brown solid is released. deposited at A colourless gas cathode relight a glowing splinter. Gas bubbles are Gas bubbles are released. released. A colourless gas A colourless gas relight a glowing  produces ‘pop’ splinter. sound wgen tested with splinter.

[ K1PP1(v) - Able to use a appropriate method to collect data ]  Able to state the ions present in electrolyte and the observations ] [ K3PP1 –  Able   Able to state a ion ion and an observation correctly ] [ K3PP2 –  Able   Able to state all the ions presents and observations correctly ] [ K3PP3 –  Able

Communication Electrolyte

Half equation

Sodium nitrate

4OH

Anode O2 + 2H2O + 4e

Copper(II) nitrate

4OH-

O2 + 2H2O + 4e

Cu2+ + 2e

Cu

Sodium sulphate

4OH-

O2 + 2H2O + 4e

2H+ + 2e

H2

-

Cathode 2H + 2e H2 +

[K4PP1- Able to write all the half equations correctly]

Interpreting Data  Able to [K4PP2 –  Able name the products  formed at anode and cathode correctly]

Conclusion

Electrolyte

Sodium nitrate Copper(II) nitrate Sodium sulphate

Name of product Anode Oxygen gas Oxygen gas Oxygen gas

Cathode Hydrogen gas Copper solid Hydrogen gas

The hypothesis is accepted. [K4PP3- Able to state the hypothesis is accepted or rejected ]

END