Post on 11-Jul-2020
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
Molecules and group ions as REDOX Agents
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+
Everyday uses of Oxidising Agents
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.
Everyday uses of Oxidising Agents
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
Everyday uses of Oxidising Agents
It has been used in fish ponds to treat common fish pathogens such as gill parasites and external bacterial and fungal infections
Everyday uses of Oxidising Agents
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
Everyday uses of Oxidising Agents
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
Everyday uses of Oxidising Agents
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.
Everyday uses of Reducing Agents
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)
Everyday uses of Reducing Agents
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
Molecules and group ions as REDOX 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