ELECTRICITY AND CHEMISTRYLEARNING OBJECTIVES. To define electrolysisTo predict that metals are formed at the

negative electrode (cathode) and that nonmetals (other than hydrogen) are formed at the positive electrode

(anode )To predict the products of the electrolysis of a

specified binary compound in the molten state.Give examples of electrode products in the

electrolysis of (1) molten lead (II) bromide.

WARM UPWhat are condctors?Give example.What are insulators?Give example.

ElectrolysisElectrolysis :-Is the process of breaking

down of compounds using electricity. It is used in large scale industrial processes to produce important chemicals like aluminium and chlorine.

Electrolytes' :- Compounds that can conduct electricity are called electrolytes

Non -Electrolytes :- Compounds which cannot conduct electricity are non electrolytes.

CONDITIONS FOR ELECTROLYSIS1. ELECTROLYTE 2. Direct current 3. Electrodes Anode :- The electrode connected the

positive terminal of the power supply. Cathode:-The electrode connected the

negative terminal of the power supply. The cations moves to cathode. The anions moves to anode.

Electrolysis of lead (II) bromideLead (II) bromide (PbBr2) is ionically bonded and

contains Pb2+ ions and Br- ions. When the solid is melted and a voltage is applied the ions are able to move . The positive lead ions move to cathode and the negative bromide ions move to the positive electrode anode. The electrodes are usually made of carbon which is inert. The products of the electrolysis are lead and bromine. Silvery deposits of lead form near the the bottom of the dish and brown bromine vapour the anode

Cathode :-Pb 2+ + 2e- → PbAnode :- 2Br- (I) → Br2 +2e-

Electrolysis of Pb Br2

ASSESMENTWhat is meant by electrolysis?What is the name given to positive

electrode?What two conditions must exist for a

substance to be an electrolyte and allow an electric current to pass through it ?

Write the half reactions in the anode and cathode.

Learning ObjectivesTo identify the products at the cathode and

anodeDuring the electrolysis of concentrated HCl To write the half reactions at the anode and

cathode.To identify the products at the cathode and

anode During the electrolysis of concentrated and

dilute sodium chloride.

WARM UPWhat are cations and anions?What is cathode? Which ions will move to

cathode?What is anode ? Which ion will move to

anode?

Electrolysis of concentrated HClWhen concentrated HCl is electrolysed

Hydreogen forms as a colourless gas at the caathode and chlorine as a pale green gas at the anode.

HCl →H+ + Cl-Inert graphite is used as electrodes.At cathode H+ ions will be discharged2H+ + 2e- →H2At anode 2Cl- → Cl2 +2e-

ELECTROLYSIS OS CONCENTRATED AQUEOUS NaClWhen ionic compound NaCl dissolves in water the

sodium and chloride ion separates and are free to move . In additon the water provides H+ and OH- ions

NaCl →Na+ +Cl-H2O ↔ H+ +OH-At cathode :- Two ions Na+ and H+ moves but only H+ ions

discharge . The sodium remains in solution. 2H+ +2e- → H2 (g)

At anode :- Two ions Cl- and OH- . If the solution is concentrated Cl – ions will be discharged.( If the solution is dilute OH- ions will be discharged in anode and oxygen will be liberated )

Diagram

ELECTROLYSIS OF NaCl

2Cl- →Cl2 +2e-The chloride ion is give up electrons and

form chlorine molecules.The sodium ion and hydroxide remains in

solution an dit becomes highly alkaline.( NaOH is formed )

Assement1. What is an inert electrode?2. What are the products obtained during

the electrolysis of HCl?3(a). Write the half reactions taking place in

anode and cathode during the electrolysis of aq concentrated NaOH solution.

(b) Why the solution becomes alkaline ?

Learning objectives The electroplating of metals : To predict

the anode and cathode. To give the uses of electroplating The uses of copper and aluminium in

cables

WARM UPHave you seen silver plated spoon?What is the use of that?

ELECTROPLATING It is the process of coating an object with a thin film of

metal using electrolysis. For example cheap metals like steel or nickel can be coated with silver or gold.

Uses (1) To improve the appearance of of metals (2) Prevents the corrosion of the metals.Silver plating of a spoon. Silver is used as anode and the spoon to be coated as

cathode.At the anode silver loses electrons and forms silver ionsAg →Ag + +e-At the cathode each silver ions accepts an electron and gets

deposited as silver .Ag+ +e-→Ag Silver nitrate is used as electrolyte. The mas of cathode

increases, which is equal to the decreases in mass at anode.

diagram

Uses of copper and aluminum in cablesMetals like copper and aluminum are good

conductors of electricity. They have free electrons in their structure which allows them conduct electricity.

Copper is used in electrical wiring because it is ductile, a flexible plastic material is used as an insulator to surround copper.

Aluminum is often used than copper due its low density but it is not so strong ,so for its use in overhead cables it is wrapped in a central core of steel.

ASSESMENTWhat is meant by electroplating?What are the uses of electroplating?In silver plating of a spoon what is used as

cathode and what is the anode?

AssesmentWhat is meant by ductile?Which is the metal used in electrical wiring?Why aluminium is used more than copper?Why Cu and Al can conduct electricity?

Learning objectives Outline the manufacture of(1) aluminum from pure aluminum oxide in

molten cryolite .(ii) To findout where aluminium is formed

(iii) Why the carbon electrodes are replaced?

WARM UPWhat are the uses of aluminium?What are minerals?What is an ore?

Manufacture of aluminiumAluminium is extracted from the ore bauxite.Aluminum oxide is extracted from bauxite by

purification.It is insoluble in water and has high melting

point 2045 C It is dissolved in cryolite at about 950 C This allows the ions to move when an electric

current is passed.Anode :- carbonCathode :- carbon lined steel case.

Redox equations – aluminiumWhat processes occur at the electrodes during the electrolysis of aluminium oxide (Al2O3)?

What is the overall equation for this extraction by electrolysis?

At the negative electrode:

Al3+ + 3e- Al (reduction)

At the positive electrode:

2O2- O2 + 4e-

(oxidation)

aluminium oxide aluminium + oxygen

2 Al2O3 (l) 4 Al (l) + 3 O2 (g)

reactionsAt cathode aluminium is formed.Al3+ + 3e-→AlAt anode oxygen is formed2O2- →O2 +4e-The over all equation 2 Al2O3 →4Al +3O2

The oxygen reacts with the carbon anodes to form carbon dioxide which escapes , so the rods need to be replaced .

This method is very expensive because large amount of electricity is used.

In this aluminium ion is reduced and oxide ion is oxidised.

Assesment In the manufacture of Al why cryolite is

used?At which electrode Al is formed?Why is it necessary to replace carbon

electrodes regularly?Write the half reactions for the formation of

Al and oxygen.

LEARNING OBJECTIVESTO IDENTIFY THE PRODUCTS ON THE

CATHODE AND ANODE ON THE ELECTROLYSIS OF BRINE SOLUTION.

TO FIND OUT THE ARRANGEMENT OF ELECTROLYSIS OF BRINE SOLUTION

WARM UP What is product obtained in the cathode

when concentrated NaCl is electrolysed. Why hydrogen is displaed at the cathode

not sodium?

Manufacture of sodium hydroxide and chlorine NaOH and Cl2 are manufactured by the electrolysis of

concentrated NaCl (brine ) in a diaphragm cell This is called chlor alkali process. Four ions are involved here Na+ ,Cl-, H+ ,OH- Na+ and H+ are attracted to the cathode. Cl- and OH- are attracted towards anode. At cathode :- Sodium is more reactive than hydrogen ,so only the

hydrogen ions change to form molecule. 2H+ + 2e- → H2

At anode:- Both OH- and Cl- are attracted to the anode but only Cl ions gets changed to form molecule.

2Cl- →Cl2 +2e- The remaining solution contains the ions Na+ and OH- so it is sodium

hydroxide solution.

Uses of sodium hydroxide and chlorine. sodium hydroxide ↓

bleach

Soap

paper

CHLORINE

BLEACH

Hydrochloric acid

Sterilize

drinking water

ASSESMENTWhat is brine solution?Where is chlorine gas collected ? What is

the colour of the gas?Why a diaphragm cell is used?What are the uses of sodium hydroxide ?Give two uses of chlorine.