redox – part 2
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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 PresentationTRANSCRIPT
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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.
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Task: Match up the formulas with theircorrect names
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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.
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Naming CompoundsNaming Compounds
??
??
What are the missing
oxidation numbers here for Manganese and Chromium, respectively?
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Task Answer – sometimes, instead of using the systematic name, scientists still use the traditional
names for some substances.
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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.
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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.
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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:
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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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QuestionsQuestions
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AnswersAnswers
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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.
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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
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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.
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More Oxidising AgentsMore Oxidising Agents
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More Oxidising AgentsMore Oxidising Agents
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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.
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More Reducing AgentsMore Reducing Agents
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More Reducing AgentsMore Reducing Agents
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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.
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Worked Example…..cont….Worked Example…..cont….
X5
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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
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Worked Example 2…Worked Example 2…
Again, start with the half
equations
Have a gobefore you turn tothe next slide for
the answer
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Worked Example 3…Worked Example 3…
Again, start with the half
equations
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Or
?
X
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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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QuestionsQuestions
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AnswersAnswers