electrochemistry1

E/plating

The process of BREAKING DOWN an electrolyte into CONSTITUENT ELEMENTS by passing ELECTRIC CURRENT through it.

Silver

Iron ring

AgNO3

molten Electrode Half equation Products

ELECTROLYSIS

Observation

Cathode (-) Ag+ + e

Anode (+)

Ag

Silver atom Grey shiny solid deposited

Ag

Ag++ e

Silver ions Anode become thinner

Electrolyte Purification Electrode Ions presence

Cathode (+) Anode (-) Br- , Pb2+

Moving of ions

Br-

Half equation Products

2BrBr2 + 2e Bromine gas Brown gas released

Observation

Impure Cu

Pb2+ + 2e Lead




Pb

Grey solid formed




Aqueous

Compound that CONDUCT ELECTRICITY in MOLTEN or AQUEOUS STATE undergoes CHEMICAL CHANGES

CuSO Electrode Half equation Products Observation

CONCENTRATION

POSITION in ECS Carbon

OH-, Cl-

Cu2+ , H+

ION PRESENCE

OH-, Cl-

Cathode

MOVING OF ION

Anode

Cathode

MOVING OF ION

Anode

Cu2+ + 2e Copper atom Brown solid deposited

Cu

PRODUCT

Oxygen gas Colourless gas released

OBSERVATION

4OHO2 + 4e

2H2O +

Blue colour of copper (II) chloride solution turn to colourless. Explain why? -Because concentration of Cu2+ ions decreases

Cu

Cu atom Brown solid deposited

Cu

Cu2+ + 2e

Cu2+ ion Anode become thinner

Position in E.C.S

Cu2+ + 2e Copper atom Brown solid deposited

Cu

half Equation (Selected ions to discharged) PRODUCT OBSERVATION

CuCl2 OH-, Cl-

ION PRESENCE

Cu2+ , H+

Anode

MOVING OF ION

Cathode

Factor of electrode

Factor of Conc.

Cu

2Cl-

Copper (II) ions Copper become thinner

Cl2 + 2e

Chlorine gas Greenish yellow gas released

Blue colour of copper (II) chloride solution turn to colourless. Explain why? -Because concentration of Cu2+ ions decreases

Cu electrode

Cu electrode

1.0 mol dm-3 CuCl2

ION PRESENCE

Position in E.C.S

Cu2+ + 2e

Anode (+)

TYPE of ELECTRODE

Cu2+ , H+

half Equation (Selected ions to discharged)

Cathode (-)

Carbon

0.01 mol dm-3 CuCl2

Position in E.C.S

pure Cu

Pb2+

Cu2+ + 2e

half Equation (Selected ions to discharged) PRODUCT OBSERVATION

Position in E.C.S

Cu2+ + 2e Copper atom Brown solid deposited

Blue colour of copper (II) chloride solution remain unchanged. Explain why ? – because rate Cu2+ change to Cu is same with rate Cu change to Cu2+

Cu

Normally observe at Cathode in an electrolysis(negative terminal) -

-

-

e-

e

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Abe Ki te

Ki te-

Electrolysis product

Confirmatory test

Observation

Chlorine gas

Greenish yellow gas released

Put a damp blue litmus paper into test tube, the litmus paper turn to red and bleach it

Bromine gas

Brown gas

Put a damp blue litmus paper into test tube, the litmus paper turn to red and bleach it

Iodine

Brown (in aqeous)/purpe in gas

Add starch solution into test tube, the starch solution turn to dark blue

Oxygen gas

Colourless gas released

Put a glowing wooden splinter into test tube, the glowing wooden splinter will light up

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Comparison between electrolytic and chemical cell

-consist of electrolyte - consist of anode and cathode - electron flow from anode to cathode

similarities

Electrolytic cell Difference s

Normally observe at anode in electrolysis (positive terminal) Electrolysis product Almost all metal (except Cu metal) Cu metal

Hydrogen gas

Observation

Confirmatory test

Grey solid formed

-

Brown solid formed

-

Colourless gas released

Put a lighted wooden splinter into test tube, a “pop” sound is produced

Voltaic cell

Two or different electrode Used to produce chemical reaction Elect to chem.

Made of Electric current Energy change

-ve terminal +ve terminal +ve terminal to ve terminal

Cathode Anode –

Flow of electron

Two different electrode Produced from chemical reaction Chem. To Elect +ve terminal -ve terminal -ve terminal to +ve terminal