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