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a.demonstrate an understanding of: iv.how oxidation number is a useful concept in terms of the classification of reactions as redox and as disproportionation b.write ionic half-equations and use them to construct full ionic equations. Redox – Part 2. Task: Match up the formulas with their - PowerPoint PPT Presentation
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Redox – Part 2Redox – Part 2a. demonstrate an understanding of:
iv. how oxidation number is a useful concept in terms of the classification of reactions as redox and as disproportionation
b. write ionic half-equations and use them to construct full ionic equations.
Task: Match up the formulas with theircorrect names
Naming CompoundsNaming Compounds
• Some elements can have more than one oxidation number.
• So to avoid confusion when naming the compounds they form, its helpful to use these numbers in their names.
Naming CompoundsNaming Compounds
??
??
What are the missing
oxidation numbers here for Manganese and Chromium, respectively?
Task Answer – sometimes, instead of using the systematic name, scientists still use the traditional
names for some substances.
Redox and Oxidation Redox and Oxidation NumbersNumbers
• An increase in oxidation number means oxidation has occurred.
• While a decrease in oxidation number means reduction has occurred.
• E.g. What would bethe oxidationnumbers foreach of the
species in thisreaction?0 -1-2 0+1 +1
Therefore,
chlorine has been reduced, and
sulphur has been oxidised.
Redox and Oxidation Redox and Oxidation NumbersNumbers
• Another example is the Thermite Reaction (click here to see it in action!!)
• But what is oxidised and what is reduced?
0 +3-2 -2+3 0
Therefore,
iron has been reduced, and
aluminium has been oxidised.
DisproportionationDisproportionation
• Is a type of reaction in which a substances both oxidised and reduced in the same reaction. E.g. the breakdown of hydrogen peroxide:
Disproportionation – another Disproportionation – another exampleexample
• The reaction of copper(I) oxide with dilute sulphuric acid:
• Study the equation carefully – what disproportionates?
• The answer is copper (Cu) which gets oxidised from +1 to +2 and also reduced from +1 to zero, in the same reaction.
• Other examples of such reactions include reactions of chlorine with water, and chlorine with hot sodium hydroxide solution.
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AnswersAnswers
Oxidation StatesOxidation States
• Some elements show a range of oxidation states.
• One colourful example is the reduction of vanadium (V) to vanadium (II) through sucessive oxidation number.
Vanadium – its different oxidation statesVanadium – its different oxidation states
Ammonium Vanadate (V) (white solid) can be added to dilute HCl to give the orange Dioxovanadium (V) ion:
VO3- + 2H+ VO2
+ + H2O
If granulated zinc is now added it reduces the vanadium over a period of several minutes and gives several colour changes:
Blue [VO(H2O)5]2+ Vanadium (IV)
Green [VCl2(H2O)4] + Vanadium (III)
Violet [V(H2O)6]2+ Vanadium (II)
+5 +5
Common Oxidising AgentsCommon Oxidising Agents
• What is an oxidising agent?– A species that reacts by oxidising something else and getting
reduced itself.
• So, as we will see, electrons in the half equations are always on the left-hand side of the equation, as oxidising agents gain electrons.
More Oxidising AgentsMore Oxidising Agents
More Oxidising AgentsMore Oxidising Agents
Common Reducing AgentsCommon Reducing Agents
• What is an reducing agent?– A species that reacts by reducing something else and getting
oxidised itself.
• So, this time, electrons in the half equations are always on the right-hand side of the equation, as reducing agents loose electrons.
More Reducing AgentsMore Reducing Agents
More Reducing AgentsMore Reducing Agents
Writing balanced equations from ionic Writing balanced equations from ionic half equations - Worked Example…half equations - Worked Example…
Firstly, write down the
half equations you
need.
Worked Example…..cont….Worked Example…..cont….
X5
Worked Example…..cont….Worked Example…..cont….
Notice, that in adding the two equations togetherThe electrons are cancelled out and not
Included in the final equation
Worked Example 2…Worked Example 2…
Again, start with the half
equations
Have a gobefore you turn tothe next slide for
the answer
Worked Example 3…Worked Example 3…
Again, start with the half
equations
Or
?
X
molecular equation
Ionic to Molecular EquationIonic to Molecular Equation• To turn an ionic equation to a molecular equation, you would
simply add the spectator ions.
• Eg. Reaction of potassium manganate (VII) solution with iron (II) sulphate solution in the presence of dilute sulphuric acid:
Ionic equation – which you work out
Add in spectator ions by using cluesIn question
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