Summary Chapter 6-CHEM SPM by Naguib Zakaria ELECTROCHEMISTRY

Electrolyte Ion Present Anode Cathode Note

Molten Lead bromide (PbBr2) PbBr2 Pb2+ + 2Br-

Ion Present :Pb2+ (CATion) Br- (ANion)

Ion present : Pb2+

Discharge : Pb2+ + 2e Pb Observation : grey solid deposit on electrode.

Ion present : Br-

Discharge: 2Br- Br2 + 2e Observation : Pungent brown gas is liberated

In molten only 2 ions are

present, so no problem to

determine which ions are goin to

be discharge on respective

electrode. Product : Lead solid Product : Bromine gas

Diluted Sodium chloride (NaCl) solution / aquoeus

NaCl Na+ + Cl-

H2O H+ + OH- Ion Present : Na+ , H+ (CATion) Cl- , OH- (ANion)

Ion present : Na+ , H+

Discharge : 2H+ + 2e H2 Observation : colourless gas is liberated at cathode

Ion present : Cl- , OH- Discharge: 4OH-

2H2O + O2+4e Observation : colourless gas is liberated at cathode

KCl, CaCl2 will yeild same

product as NaCl in this case,

because K+, Na

+ and Ca

2+ will

not choose to bes discharge at

cathode. ( refer to E.C.S)

** Anode- solute will discharge

when solution is concentrated, if

diluted refer to ECS, the lowest

ion will choose to be discharge.

Product : Hydrogen gas Product : Oxygen gas

Concentrated Sodium chloride (NaCl) solution / aqueous

NaCl Na+ + Cl-

H2O H+ + OH- Ion Present : Na+ , H+ (CATion) Cl- , OH- (ANion)

Ion present : Na+ , H+

Discharge : 2H+ + 2e H2 Observation : colourless gas is liberated at cathode

Ion present : Cl- , OH- Discharge: 2Cl- Cl2 + 2e Observation : Pungent yellowish gas is liberated at anode

Product : Hydrogen gas Product : Chlorine gas

Concentrated / Diluted Copper(II)sulphate aqueous ( using carbon / graphite / platinum electrode)

CuSO4 Cu2+ + SO42-

H2O H+ + OH- Ion Present : Cu2+ , H+ (CATion) SO4

2-, OH- (ANion)

Ion present : Cu2+ , H+

Discharge : Cu2+ + 2e Cu Observation : Brown solid deposit on cathode

Ion present : SO42-, OH-

Discharge: 4OH-2H2O + O2+4e

Observation : colourless gas is liberated at cathode

Either concentrated or diluted

Cu2+

is choose to discharge at

cathode ( refer to E.C.S)

** extra observation : Intensity

of blue colour decrease

Reason : concentration Cu2+

ion

decrease

Product : Copper solid Product : Oxygen gas

Concentrated / Diluted Copper(II)sulphate aqueous ( using copper electrode)

CuSO4 Cu2+ + SO42-

H2O H+ + OH- Ion Present : Cu2+ , H+ (CATion) SO4

2-, OH- (ANion)

Ion present : Cu2+ , H+

Discharge : Cu2+ + 2e Cu Observation : Brown solid deposit on cathode // Electrode become thicker // mass of electrode increase

Ion present : SO42-, OH-

Ionization : Cu Cu2+ 2e Observation : Electrode become thinner // mass of electrode decrease

Reactive electrode are used. So

at anode, discharge process

does not occur. Electrode will

dissolves in electrolyte to

produce ion.

** extra observation : Intensity

of blue colour remains

unchange Product : Copper solid Product : Cu2+ ion

CA

Tio

n

K+

Na+

C

a2+

Mg2

+ A

l3+

Zn2+

Fe

2+

Sn2+

Pb

2+

H+

Cu

2+

Ag+

AN

ion

F- SO

42-

NO

3-

Cl-

Br-

I-

OH

-

Easy to discharge (more electronegativity) Easy to discharge

**K+, Na+, Ca2+ from cation, F-, SO42- andNO3

- from anion : THESE ARE STABLE IONS. THEY DO NOT DISCHARGE IN WHATEVER CONDITION. THEY HAVE A STRONGER TENDENCY TO EXIST AS IONS THAN ATOMS OR MOLECULE.

Summary Chapter 6-CHEM SPM by Naguib Zakaria DIAGRAM ELECTROLYSIS USING MOLTEN ELECTROLYTE

ELECTROLYSIS USING SOLUTION / AQUEOUS ELECTROLYTE

ELECTROLYSIS COPPER (ii) SULPHATE AS ELECTROLYTE (Carbon Electrode)

ELECTROPLATING AND PURIFYING OF METAL

GAS CONFIRMATORY TEST

Gas Properties Chemical test

Oxygen Colourless gas

1. Bring glowing wooden splinter near to the mouth of test tube.

2. Glowing wooden splinter relight. 3. Oxygen gas is released.

Hydrogen Colourless gas

1. Bring lighted splinter near to the mouth of test tube

2. Fire extinguish, produce ‘pop’ sound.

3. Hydrogen gas is released.

Chlorine Pungent yellowish gas

1. Put a moist blue litmus paper in the test tube.

2. Blue litmus change to red and bleach out (white).

3. Chlorine gas is released.

Bromine Pungent brown gas

1. Put a moist blue litmus paper in the test tube.

2. Blue litmus change to red. 3. Bromine gas is released.

Summary Chapter 6-CHEM SPM by Naguib Zakaria

Anode ( negative terminal) Definition: Anode is a terminal where substance releases electrons and the oxidation process takes place. Zinc is more electropositive than copper. (Zinc stated above than copper in electrochemical series). Zinc atom will released electrons to form zinc ion.

Zn Zn2+ + 2e Zinc strip : becomes the negative terminal. Electron flow from zinc strip to copper strip. Observation at Anode: Zinc strip become thinner. (because it dissolves, refer to half equation above)

Cathode ( positive terminal) Definition: Cathode is a terminal where the substance accepts electrons and the reduction process takes place Electrons flow from zins strip to copper strip through the external circuit. Electrons are accepted by Cu2+ ions. Cu2+ ions are discharged because its position is lower than Zn2+ ion and H+ ion in ECS.

Cu2+ + 2e Cu Copper strip : becomes the positive terminal. Observation at Anode: Brown solid deposit on the copper strip. Intensity of blue colour decrease (because the concentration of Cu2+ is decreases.)

Energy change : Chemical energy Electrical Energy ** the position of two metals is in Electrochemical series determine the cell voltage. ** the further the distance between two metal in Electrochamical series, he bigger the cell voltage will be.

Salt Bridge : contains inert ions or salt that does not react with the electrolyte, example sodium chloride, potassium chloride, potassium nitrate and dilute sulphuric acid. **Function: To complete the circuit by allows the flow of ions. To prevent the two electrolyte from mixing. ** Porous pot also functioned like a salt bridge. Porous pot has fine pores to allow ions to flow through but prevent the two electrolyte from mixing