I am learning to understand redox reactions

EXAM TIPS:EXAM TIPS:

•You will be expected to write You will be expected to write half equations for the half equations for the reactions at the electrodes.reactions at the electrodes.

•In half equations, the number In half equations, the number of electrons MUST balance the of electrons MUST balance the number of charges on the ion.number of charges on the ion.

I am learning to understand redox reactions

Outcomes: Outcomes: I will demonstrate I understand at I will demonstrate I understand at Grade C byGrade C by• Recall the transfer of electrons at the anode and cathode.• Recognise oxidation and reduction at electrodes.• Predict the products of electrolysis.

Outcomes: Outcomes: I will demonstrate I understand at Grade A byI will demonstrate I understand at Grade A by• Explain the transfer of electrons in electrolysis.• Construct half equations• Explain how water affects the products of electrolysis.

Objectives: Objectives: I will understandI will understand• That electrons are transferred during electrolysis.• That electrolysis can be represented in half equations. • That water affects electrolysis.

I am learning to understand redox reactions

heat

Positive ions move to the negative electrode

(cathode) and gain electrons (Red)

Negative ions move to the positive electrode

(the anode) and lose electrons (Ox)

I am learning to understand redox reactions

What is

Oxidation?

I am learning to understand redox reactions

Oxidation •Oxidation is the gain of oxygenOxidation is the gain of oxygen

•Rust is an example of oxidation Rust is an example of oxidation

What is reduction?

I am learning to understand redox reactions

Reduction

• Reduction is the loss of oxygen Reduction is the loss of oxygen

• Metal Displacement reactions are an example of Metal Displacement reactions are an example of reduction.reduction.

lead oxide + carbon lead

carbon monoxide +

oxygen removedreduction

oxygen addedoxidation

I am learning to understand redox reactions

I am learning to understand redox reactions

Reduction and oxidation always take place together.Reduction and oxidation always take place together. Why is this type of reaction called a Why is this type of reaction called a redoxredox reaction? reaction?

redox = reduction and oxidation

Oxidation

Is

Loss of electrons

Reduction

Is

Gain of electrons

OILRIG

YOU SHOULD YOU SHOULD ALWAYS ALWAYS

WRITE THIS WRITE THIS NEXT TO THE NEXT TO THE

QUESTIONQUESTION

I am learning to understand redox reactions

magnesium + oxygen magnesium oxide

2Mg(s) O2(g) 2MgO(s)+

Magnesium burns in oxygen to form Magnesium oxide.

The Magnesium obviously is oxidised but

what happens to the oxygen?

I am learning to understand redox reactions

Redox Reactions can also be explained in the Redox Reactions can also be explained in the terms of terms of losinglosing or or gaininggaining electronselectrons

Mg Mg2+ O2-O+

oxidized(electrons lost)

reduced(electrons gained)

Mg is oxidised (lost electrons)O is reduced (gained electrons)

I am learning to understand redox reactions

In terms of oxygen

In terms of electrons

Oxidation Loss of electrons

Reduction Loss of oxygen

Copy and Complete the table...

I am learning to understand redox reactions

Half Equations

•Redox reactions involve the transfer of electronsRedox reactions involve the transfer of electrons. .

•Equations written to show what happens to the electrons during Equations written to show what happens to the electrons during oxidation and reduction are called half-equations.oxidation and reduction are called half-equations.

oxidation: Mg Mg2+ + 2e-

magnesium + oxygen magnesium oxide

2Mg (s) O2 (g) 2MgO (s)+

reduction: O2 + 4e- 2O2-

I am learning to understand redox reactions

1. Na+ + e- → _____

2. Pb2+ + ____ e- → Pb

3. Cu2+ + _____e- → ____

4. ___H+ + _____e- → H2

Oxidation orReduction?

Na

2

2 Cu

2 2

REDUCTION

REDUCTION

REDUCTION

REDUCTION

I am learning to understand redox reactions

2K+  +  ____e-  →   2K

2Cl-  -  ___e-  →    Cl2

2 REDUCTION

2OXIDATION

Oxidation or

Reduction?

I am learning to understand redox reactions

I am learning to understand redox reactions

What redox processes occur at the electrodes during the electrolysis of molten lead bromide (PbBr2)?

What is the overall equation for the electrolysis of What is the overall equation for the electrolysis of molten lead bromide with state symbols?molten lead bromide with state symbols?

At the negative electrode:

Pb2+ + 2e- Pb (reduction)

lead bromide lead + brominePbBr2 (l) Pb (l) + Br2 (g)

At the positive electrode:

2Br- Br2 + 2e- (oxidation)

ElectrolysisElectrolysis of moltenof molten PbBrPbBr22 –– redoxredox equationsequations

I am learning to understand redox reactions

We need an

• Anode (to take electrons)

• Cathode (to give out electrons)

• Pb and Br ions.

I am learning to understand redox reactions

Your Turn – Your Turn – Complete these equations with statesComplete these equations with states

• 2FeCl3(aq)

Anode(+)?

Cathode(-)?

2Fe(s) 2Fe(s) ++ 3Cl 3Cl22(g)(g)

2Cl2Cl--(aq) (aq) ClCl22(g) (g) ++ 2e 2e--

FeFe3+3+ (aq) + 3e- Fe (s) (aq) + 3e- Fe (s)

OXIDATION

REDUCTION

I am learning to understand redox reactions

How does water effect the products How does water effect the products of electrolysis?of electrolysis?

Water contains hydrogen and hydroxide ions.

When solutions of ions in water are electrolysed, hydrogen may be produced at the positive electrode.

This happens if the other positive ions are metals more reactive than hydrogen.

I am learning to understand redox reactions

Summary notesSummary notes•When positively charged ions reach the negative electrode they gain electrons to become neutral atoms. Gaining electrons is called reduction, so the positive ions have been reduced. Ions with a single positive charge gain one electron and those with a 2+ charge gain 2 electrons.

•At the positive electrode, negative ions lose electrons to become neutral atoms. This is oxidation. Some non-metal atoms combine to form molecules, for example bromine forms Br2.

•We can represent the changes at the electrodes by half equations. For lead bromide.

At the negative electrode: Pb2+ + 2e- Pb

At the positive electrode: 2Br- Br2 + 2e-

•Water contains hydrogen and hydroxide ions. When solutions of ions in water are electrolysed, hydrogen may be produced at the positive electrode. This happens if the other positive ions are of metals more reactive than hydrogen.

•Oxidation is loss (OIL) reduction is gain (RIG).

•In half equations the number of electrons must balance the number of charges on the ion.

I am learning to understand redox reactions

Check your understandingCheck your understanding1. What happens in electrolysis to copper ions, Cu2+,

at the negative electrode?2. What happens in electrolysis to chloride ions, Cl-,

at the positive electrode?3. Why are ions of metals always reduced in

electrolysis?

ANSWERS:

1. They are discharged, gain electrons and are reduced to form copper atoms.2. They are discharged, lose electrons and are oxidised to form chlorine atoms

which then bond to form chlorine molecules (diatomic molecules)3. All metals form positive ions so they are attracted to the negative electrode

where they gain electrons.

CLICK AGAIN FOR THE ANSWERSCLICK AGAIN FOR THE ANSWERS

I am learning to understand redox reactions

Extra Notes

I am learning to understand redox reactions

I am learning to understand redox reactions

I am learning to understand redox reactions

I am learning to understand redox reactions

I am learning to understand redox reactions