Oxidising and Reducing Agents - LT Scotland · 2019-12-14 · I can define oxidising agent and reducing agent in terms of electrons. I can identify oxidising agents and reducing agents

CfE Higher Chemistry

Unit 3: Chemistry in Society

Oxidising and Reducing Agents

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Lesson Starter: Decide whether each of the following reactions involve oxidation

or reduction.

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(You may find it helpful to use the Data Booklet.)

Learning Outcomes :

Ion-electron and Redox Equations 08/12/2017

• I can complete an ion electron half equation when the reactant and product is known.

• I can combine ion-electron equations to produce a redox equation.

Redox Revision of N5 • An OXIDATION reaction is one where electrons are lost

Zn(s) Zn2+(aq) + 2e-

• A REDUCTION reaction is one where electrons are gained

Cu2+(aq) + 2e- Cu(s)

• A REDOX reaction is one in which both OXIDATION and REDUCTION occur

Zn(s) + Cu2+(aq) Zn2+

(aq) + Cu(s)

Oxidation & Reduction

O I L R I G

xidation s oss eduction s ain

Remember!!!

Experiment:

EXPERIMENTS 3.8

Redox Reactions

Experiment:

1. Magnesium and dilute hydrochloric acid. Add 2 cm-length of magnesium to a test tube containing 2 cm-depth

of dilute hydrochloric acid, concentration 2 mol l-1. Collect the gas produced and identify it.xcv

2. Zinc and copper(II) sulphate solution Drop a piece of zinc into a test tube containing 2 cm-depth of

copper(II) sulphate solution. 3. Sodium sulphite and iodine solution Add iodine solution to a depth of 1 cm to a test tube. Add sodium

sulphite, 1 spatula at a time, until there is a noticeable change in the solution.

4. Acidified potassium permanganate solution and potassium iodide solution

Add a few drops of an acidified solution of potassium permanganate to 2 cm-depth of potassium iodide solution. Extract a few drops of the the product solution and add to starch.

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Carry out each of the following test tube experiments.

Experiment:

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Notes

For each of the test tube experiments:

1) Briefly describe each of the experiments.

2) Use the Data Booklet to write ion-electron equations for the oxidations and reductions.

3) Combine the oxidations and reductions to form the redox reactions.

Writing Redox Reactions

Example: Magnesium reacts with a solution of silver (I) ions to form silver and a solution of magnesium (II)

ions.

1. List reactants and products

Reactants: Mg and Ag+

Products: Mg2+ and Ag

2. Write the reduction reactions found in the data booklet

Mg2+(aq) + 2e- Mg(s)

Ag+(aq) + e- Ag(s)

3. Rearrange equations to show an OXIDATION reaction and a REDUCTION reaction

• Oxidation Mg(s) Mg2+(aq) + 2e-

(reversed because Mg is a reactant-not

product)

• Reduction Ag+(aq) + e- Ag(s)

4. Multiply each equation so that electrons are equal in number.

Oxidation Mg(s) Mg2+(aq) + 2e-

Reduction 2Ag+(aq) + 2e- 2Ag(s)

5. Add reactions together, eliminating the electrons

• Redox

Mg(s) + 2Ag+(aq) Mg2+

(aq) + 2Ag(s)

Practice Question

1. Lithium + copper ions

2. Sodium + zinc ions

3. Aluminium + tin ions

4. Calcium + iron ions

5. Magnesium + silver ions

6. Zinc + copper ions

7. Potassium + aluminium ions

8. Iron + copper ions

Write the REDOX reactions

1. 2Li + Cu2+ 2Li+ + Cu

2. 2Na + Zn2+ 2Na+ + Zn

3. 2Al + 3Sn2+ 2Al3+ + 3Sn

4. Ca + Fe2+ Ca2+ + Fe

5. Mg + 2Ag+ Mg2+ + 2Ag

6. Zn + Cu2+ Zn2+ + Cu

7. 3K + Al3+ 3K+ + Al

8. Fe + Cu2+ Fe2+ + Cu

Success Criteria:

Next Lesson:

I can complete an ion electron half equation when the reactant and product is known.

I can combine ion-electron equations to produce a redox equation.

Ion-electron and Redox Equations 08/12/2017

Lesson Starter:

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Learning Outcomes :

Elements as RedOx Agents 08/12/2017

• I can define oxidising agent and reducing agent in terms of electrons.

• I can identify oxidising agents and reducing agents in redox reactions

• I can use electronegativity to predict which elements tend to lose electrons and which tend to gain electrons when they form ions.

• I can use electronegativity to predict which elements can act as reducing agents and which can act as oxidising agents.

• I can state which group in the Periodic Table contains the strongest reducing agents and which group contains the strongest oxidising agents.

• I can use the Electrochemical Series to determine the effectiveness of oxidising and reducing agents.

Experiment:

EXPERIMENT / DEMO 3.9

Halogen Displacement

Christmas Tree

Displacement: Christmas tree

Halogen Displacement

Chlorine water

Bromine water

Iodine water KBr added

KI added

KCl added

KI added

KCl added

KBr added

Colour change Yes Yes No Yes No No

Write an equation to show the reactions which are taking place in tubes 1,2 and 4

Halogen Displacment

• The more reactive halogens are able to displace less reactive halogens, so in tube 4 the bromine is able to displace the iodine from the KI and a deeper iodine (red/ orange colour is observed)

• 2KI(aq) + Br2 (aq)→2KBr(aq) + I2 (aq)

Orange red/orange

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Oxidising & Reducing Agents

An OXIDISING agent is a substance which ACCEPTS ELECTRONS

Non-metals tend to have HIGH electro-negativities (STRONG pull for bonding electrons) and form

NEGATIVE ions by GAINING electrons.

By gaining electrons they themselves are REDUCED

Example

2Li + 2Li+ + Cu

An OXIDISING agent is a substance which

ACCEPTS ELECTRONS

Cu2+

Example

2Na + 2Na+ + Zn

An OXIDISING agent is a substance which

ACCEPTS ELECTRONS

Zn2+

Oxidising & Reducing Agents

An REDUCING agent is a substance which DONATES ELECTRONS

Metals tend to have LOW electro-negativities (WEAK pull for bonding electrons) and form POSITIVE ions by LOSING electrons.

By losing electrons they themselves are OXIDISED

Example

+ Zn2+ 2Na+ + Zn

An REDUCING agent is a substance which

DONATES ELECTRONS

2Na

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Weakest Oxidising Agents

Strongest Oxidising Agents

Strongest Reducing Agents

Weakest Reducing Agents

Practice Question

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Success Criteria:

Next Lesson:

I can define oxidising agent and reducing agent in terms of electrons. I can identify oxidising agents and reducing agents in redox reactions I can use electronegativity to predict which elements tend to lose electrons and which elements tend to gain electrons when they form ions. I can use electronegativity to predict which elements can act as reducing agents and which can act as oxidising agents. I can state which group in the Periodic Table contains the strongest reducing agents and which group contains the strongest oxidising agents. I can use the Electrochemical Series to determine the effectiveness of oxidising and reducing agents.

Elements REDOX Agents 08/12/2017

Learning Outcomes :

Molecules and group ions as REDOX Agents

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• I can use the Electrochemical Series to identify oxidising agents and reducing agents.

• I can predict how acidified dichromate and acidified permanganate react.

• I can predict how hydrogen peroxide and carbon monoxide react.

• I can state examples of uses for oxidising agents

Experiment:

EXPERIMENTS / DEMO 3.10


Writing Complex Ion-Electron Equations (Oxy Anions)

e.g. Sulphite SO32-

Permanganate MnO4-

Dichromate Cr2O72-

e.g. Permanganate ions can be reduced to Mn2+. Write the ion-electron equation for the reduction.

i.e. MnO4- Mn2+

Rules

E 1. Balance the no. of atoms of the ELEMENT being reduced or oxidised

MnO4- Mn2+

O 2. Balance the OXYGEN atoms by adding H2O

MnO4- Mn2+ + 4H2O

H 3. Balance HYDROGEN atoms by adding H+

MnO4- + 8H+ Mn2+ + 4H2O

C 4. Balance CHARGE by adding electrons

MnO4- + 8H+ + 5e- Mn2+ + 4H2O

2+ 2+

Eat Only Hot Curries

Example 1: Oxidation of SO32- SO4

2-

E SO32- SO4

2-

O SO32- + H2O SO4

2-

H SO32- + H2O SO4

2- + 2H+

C SO32- + H2O SO4

2- + 2H+ + 2e-

Example 2: Thiosulphate being oxidised to sulphite

E S2O32- 2SO3

2-

O S2O32- + 3H2O 2SO3

2-

H S2O32- + 3H2O 2SO3

2- + 6H+

C S2O32- + 3H2O 2SO3

2- + 6H+ + 4e-

Exercises Try and write the ion electron Equation for these: 1.) MnO4- Mn2+ 2.) Pb2+ PbO2

3.) ClO- Cl-

4.) Mn2+ MnO2

4H2O

2H2O

H2O

2H2O

8H+

4H+

4H+

4H+

6e-

2+

2+ 8+

4+

2e-

4e-

3+ 1-

2+ 4+

2e-

Exercises Try and write the ion electron Equation for these: 5.) Sb SbO+ 6.) VO2+ V3+

7.) HOBr Br2

8.) C2H5OH CH3CHO

H2O

H2O

2H2O

2H+

2H+

2H+

2H+

3e-

4+

3+ 0

3+

e-

2e-

2+ 0

0 2+

2e-

2

Experiment:

EXPERIMENTS / DEMO 3.11

Uses of Oxidising Agents

H2O2 H2O

Everyday uses of Oxidising Agents

Hydrogen peroxide– H2O2

The oxidation process is also an effective means of breaking down coloured compounds making oxidising agents ideal for use as “bleach” for clothes and hair.

2H+ 2e- 2

0 2+


Hydrogen peroxide, H2O2(aq) can be used to bleach hair and it behaves here as an oxidising agent. In the reaction, coloured pigments in the hair, related to the pigment melanin are oxidised to colourless substances.


Potassium Permanganate – KMnO4

Oxidising agents are widely employed because of the effectiveness with which they can kill fungi and bacteria, and can inactivate viruses.

Potassium permanganate solution will react with any organic matter in a pond including algae, bacteria, fish, particulate and dissolved organic, and organic bottom sediments


It has been used in fish ponds to treat common fish pathogens such as gill parasites and external bacterial and fungal infections


Chlorine kills bacteria though a fairly simple chemical reaction. The chlorine solution you pour into the water breaks down into many different chemicals, including hypochlorous acid (HOCl)

HClO Cl2


The hypochlorus acid is a strong oxidising agent and kills microorganisms by removing electrons from the bacteria destroying the cell walls and enzymes and structures inside the cell, rendering them harmless.

2H+ 2

0 0

2H2O


Luminol can be oxidised by a solution of bleach to an aminophthalate ion which is produced in an excited state and emits light as it drops back into a ground state.

Everyday uses of Reducing Agents

They are described as anti-oxidants and are used to sterilise glass bottles in wine-making and are present in some foods. If you see E220 amongst the products of a food stuff, this represents sulphur dioxide.


Aran sweaters used to be bleached using sulphur dioxide gas on the wet sweaters. The reaction involves the dissolving of the gas to make a solution containing hydrogen sulphite. This produces some sulphite ions.

SO2(g) + H2O(l) → H2SO3 (aq)


SO32-(aq) + → SO4

2-(aq) 2H+

2- 0

H2O 2e-

As the reaction is oxidation, SO2(g) in water and SO3

2-(aq) are examples of a bleach which is a reducing agent.

Success Criteria:

Next Lesson:

I can use the Electrochemical Series to identify oxidising agents and reducing agents.

I can predict how acidified dichromate and acidified permanganate react.

I can predict how hydrogen peroxide and carbon monoxide react.

I can state examples of uses for oxidising agents


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Weakest Oxidising Agents

Strongest Oxidising Agents

Strongest Reducing Agents

Weakest Reducing Agents

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Learning Outcomes :

Past Paper Questions 08/12/2017

2014 MC 37

2011 MC 37

2011 MC 38

2009 MC 37

2010 MC 39

2008 MC 38

2013 4

2013 16

2012 5b

2009 18a

2008 17a

Documents

Oxidising and Reducing Agents - LT Scotland · 2019-12-14 · I can define oxidising agent and reducing agent in terms of electrons. I can identify oxidising agents and reducing agents