REDOX REACTIONS PT3 Electrolytic cell

Electrolytic cells are spontaneous or non-spontaneous

Non-spontaneous

Difference between galvanic cell and electrolytic cell in terms of energy conversion

• Chemical energy to electrical energy

• Electrical energy to chemical energy

Define electrolytic cell

Is an electrochemical cell in which non-spontaneous redox reactions occur at the electrodes. Electrical energy is converted to chemical energy

What must be applied in order to maintain the electrode reactions and does this affect the spontaneous aspect

Electrical energy with a DC current (external source)

Yes,this is why electrolytic cells are non-spontaneous

True/false

In a electrolytic cell the reaction is also exothermic and the cell potential is positive

False

Endothermic and negative

What must the electrolyte be(2)

• Ionic substance

• Molten/dissolved in distilled water

Why is an electrical current needed

Since ionic substances are in crystal lattices(ions can't move freely). The charges from current can move freely and therefore causing the reaction

Define electrolysis

Electrolysis is the chemical process in which electrical energy is converted to chemical energy. It is the use of electrical energy to produce a chemical change

What are two unreactive electrodes in electrolytic cells

-graphite

-carbon

What's ONE MAJOR thing about the electrodes

Anode is positive

Cathode is negative

But reduction is still at the cathode and oxidation still at anode

What's the state symbol for molten substances and state symbol for dissolved

-(L)

-(aq)

Anions are attracted to ___and are oxidised there

Cations are attracted to___ and are reduced there

Anode

Cathode

Are you free to move when substance is melted or dissolved

109% yes

What happens during the oxidation of water

What happens during the reduction of water

• Oxygen gas forms by anode

• pH decreases( more H3O ions since presence of H ions increase and bind with water )

• Hydrogen gas forms by cathode

• pH increases(more OH ions)

For low anion concentrations (lots of water,few anions)

For high anion concentrations(saturated solution)

Strongest reducing agent will oxidise

Anion will always oxidise

At the negative cathode

Strongest oxidising agent will always reduce

What are the 3 main applications of electolysis

Electroplating

Electrofing of copper

Preparation of chlorine gas,hydrogen gas and sodium hydroxide

What is electroplating

• What is it literally

• Whats the tow uses

• Are the half reactions done with the same metal

• Covering metal object with a thin layer of another metal

• Make it look better+protect cheap metal(nickel/bronze)

• Both half reactions are from the same metal

What's the anode,cathod and electrolyte mixture

• Precious metal rod(gold/silver)

• Object that needs plating(i.e nickel spoon)

• Precious metal nitrate and potassium cyanide

What two things does cynadie help with

• Keeping consistent precious metal concentration

• Increases electrical conductivity

• Ensures effective plating

How does electroplating work

What remains constant during electroplating

The concentration of previous metal

What is electrorefining of copper

Impure copper being purified through electolysis

The deposits on cathode is the pure copper

Impure copper is used for anodes

What is anode silt

Less reactive(weaker reducing agentslike silver,gold and platinum) sink to the bottom of the cell

Which solution is normally used for copper electrorefining

Acified copper sulphate

The electrolysis of concentrated NaCl solution is used in the chloro-alkali industry

• What's another name for [NaCl(aq)]

• What is formed from this type of electrolysis

• Brine

• Cl gas

• NaOH

• H gas

• NaOH(aq) (caustic soda)

How does membrane cell work

• Oxidation half-call and reduction half cell are separated by the cation exchange membrane

• Membrane only allows cations through

• Na+ move from anode half cell to cathode

• OH ions can't move to anode from the cathode

• NaCl is pumped Into oxidation half-cell

What's formed at the anode and what forms at cathode at the membrane cell

And what is sodium

• Cl gas cause it's very concentrated so will oxidise instead of H2O

• Hydrogen gas(from water) since it's a stronger oxidising agent

• Sodium ions are spectator ions

Advantages of membrane cell

• Most Environmentally friendly cell

• Cheaper than other two

• Produces very our product

Disadvantages of membrane cell

• Cl gas can't be inhaled

• H gas is combustible

• NaOH is corrosive and should not be in ground water

• High tech membrane can get clogged by impure cations

What 3 formulas can you use to find charge