Electrolytic ProcessesC3.3

Love, Heba

Electrolysis – Basic Facts you need to know.

Remember: Molten = Melted ( liquid)Aqueous = Dissolved in solution

Key points :• The ions in the electrolyte MUST be free so they can move towards an

electrode • Electrolysis uses electricity to decompose a compound • The Cathode ( -ve) attracts cations ( +ve) , and the anode ( +ve) attracts

anions ( -ve) • Electricity is supplied from a DC • For an electric circuit to be complete , there must be a flow of electrons. Positive Anode – Electrons are taken away from ionNegative Cathode - Electrons which are taken away are given to other ions.

Molten NaCl

Electrolysis of Molten Substances.

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++++++

Cathode-ve

Anode+ve

+

+

--

𝐶 𝑙2Sodium Is

produced at the

Cathode

Chlorine is Produced

at the Anode

Details… You need to know electrolysis of : Sodium Chloride

𝑁𝑎+¿ ¿ 𝐶𝑙−

Reduced at Cathode ( gains electron)

𝑁𝑎

Oxidised at Anode ( loses electron)

Joins with another Cl atom ( remember its diatomic )

𝐶𝑙2

OIL RIG = OXIDATION IS LOSS REDUCTION IS GAIN

Na

Sodium…

Collected and used as/in:

Street lamps Coolant in some nuclear reactors!

Molten Lead Bromide

𝑃𝑏2+¿¿ 𝐵𝑟−

Goes to: CathodeReduction: Gains two electronsBecomes: Pb

Goes to: AnodeOxidation : loses electronJoins with another Br- , overall two electrons lost Becomes:

𝑃𝑏2+¿+2𝑒−→𝑃𝑏¿ 2𝐵𝑟−→𝐵𝑟 2+2𝑒−

Electrolysis of Solutions

Before starting , you need to know that when salts are dissolved in water, there is also Hydrogen and (OH) ions floating about.

Just remember that:

At Cathodeif the metal is less

reactive than hydrogen – it will discharge to the

cathode ( go to ) , but if

there is metal that is more reactive than hydrogen,

hydrogen will go to the cathode.

At Anode“the simplest” ion

will go to the anode. E.g

Chlorine will be discharged rather than Hydroxide. And Hydroxide

would discharge instead of (SO4)

Electrolysis: Concentrated Sodium Chloride

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++++++

Cathode-ve

Anode+veKey points:

• Hydrogen is less reactive than Sodium

• Chlorine is more simple than (OH)

• Sodium hydroxide is left in the bottom.

• Hydrogen is collected at the cathode

• Chlorine is collected at the anode.

𝐻+¿ ¿

𝐻+¿ ¿ 𝐶𝑙−𝐶𝑙−

𝑂𝐻− 𝑂𝐻−𝑁𝑎+¿ ¿𝑁𝑎+¿ ¿

Electrolysis of other Compounds you need to know

Electrolyte Half equations At the Cathode

At the Anode

Cathode: Anode:

Copper Chlorine

Cathode: Anode:

Copper Oxygen

Cathode: Anode:

Hydrogen Oxygen

NaCl Cathode: Anode:

Hydrogen Chlorine

Electrolysis using copper Electrodes.

Before we start: • Pure copper is the cathode (-ve)

• Impure copper – Copper (II) Sulphate is the anode ( +ve)• The main purpose for this is:

Copper can be extracted from its ore using carbon ( heating it up with carbon) , but you do not obtain the

finest, purest copper – so electrolysis is required. • Remember , just like any electrolysis process : GAIN ELECTRONS = REDUCTION = AT CATHODE LOSS OF ELECTRONS = OXIDATION = AT ANODE

The process… 1) You start off with a big fat chunk of imputer copper (II) Sulfate as the

anode and a tiny bit of pure copper as the cathode.2) The anode contains Cu ions ( Cu+2) we want to obtain this – How? 3) Supplying electricity provides cathode with electrons 4) These electrons in the cathode attract the Cu ions from the impure

Copper5) The impurities fall in the base of the container called “sludge”6) Cu is oxidised in the anode as it loses electrons 7) Cu is reduced in the cathode as it gains electrons to become a Cu atom

Copper atoms been oxidised

Copper ions been reduced into Pure copper atoms.

Mass of Anode and CathodeObviously the mass of the Anode will decrease and the mass

of the Cathode will increase… To test this:

1) Weigh the anode and cathode before electrolysis 2) Place the electrodes in the copper Sulfate solution

3) Connect to DC 4) After 5 minutes remove the electrodes from electricity

source and dry them 5) Weigh the anode and cathode again.

Electroplating

Basics…Electroplating is coating the surface if a metal with

another metal using electricity! Remember:

- The cathode: The metal that will be plated - The anode- the bar of metal used for plating

The ions from the solution ( electrolyte ) moves towards the metal cathode. The Anode keeps the ions

in the solution “topped up”

Coating with Silver• Electrolyte could be : silver nitrate or silver

sulfate! • Anode: Silver block ( to top up the electrolyte

with ions) • Cathode: E.g Brass

h𝐶𝑎𝑡 𝑜𝑑𝑒 : 𝐴𝑔+¿+𝑒−→ 𝐴𝑔¿

𝐴𝑛𝑜𝑑𝑒 : 𝐴𝑔→   𝐴𝑔+¿+𝑒−¿

Electroplating uses:

Use 1 – Decoration – e.g Jewellery is plated with silver or gold this makes their appearance much better and makes it

more shiny and attractive

Use 2 – Prevention of corrosion– Some metals corrode e.g Iron ( due to oxygen) – some household objects like cutlery

are coated with an unreactive metal to stop it from corroding e.g Nickel or chromium