5.7 Redox Reaction

REDOX REACTION REDUCTION

OXIDATION

By the end of the topic, students should be able to: □ Know what is meant by a redox reaction. □ Define oxidation and reduction in terms of oxygen gain/loss and use it to show where oxidation and reduction take place in a reaction. □ Define oxidation and reduction in terms of hydrogen loss/gain and use it to show where oxidation and reduction take place in a reaction. □ Define oxidation and reduction as electron loss/gain and use it to show where oxidation and reduction take place in a reaction. □ Find the oxidation state of an element in a compound. □ Find the formula of a compound from its name containing an oxidation number. □ Define oxidation and reduction in terms of changes in oxidation state and use it to show where oxidation and reduction take place in a reaction. □ Describe the colour change when potassium iodide is used to test for an oxidizing agent. □ Describe the colour change when potassium manganate (VII) and potassium dichromate (VI) are used to test for a reducing agent. □ State some common oxidizing and reducing agents.

Please tick in the box if you can do the above.

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OXIDATION AND REDUCTION  In chemical reactions, oxidation and reduction is an important concept and it has applications in many topics.  There are several ways of describing oxidation and reduction. They can be described in terms of: 1) loss and gain of oxygen 2) loss and gain of hydrogen 3) loss and gain of electrons 4) change of oxidation state 1) LOSS AND GAIN OF OXYGEN  Gain of oxygen in a reaction is __________________.  Loss of oxygen in a reaction is __________________. Example 1:

Oxidising and reducing agent  What is an oxidizing agent? A substance that causes another substance to be _______________. An oxidizing agent is _____________ when it oxidizes another substance.  What is a reducing agent? A substance that causes another substance to be _______________. A reducing agent is _______________ when it reduces another substance. ⇒ From example 1 above, state the oxidizing agent and the reducing agent. Oxidising agent: Reducing agent: 2

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 Please proceed to do exercise from: CHEMISTRY INSIGHTS, Pg. 325, Questions, Quest. 1-2 2) LOSS AND GAIN OF HYDROGEN  Loss of hydrogen in a reaction is ______________________.  Gainof hydrogen in a reaction is _______________________. Example 2:

⇒ From example 2 above, state the oxidizing agent and the reducing agent. Oxidising agent: Reducing agent:  Please proceed to do exercise from: CHEMISTRY INSIGHTS, Pg. 325, Questions, Quest. 3 3) LOSS AND GAIN OF ELECTRONS  Loss of electrons in a reaction is _________________.  Gain of electrons in a reaction is _________________. Example 3:

⇒ From example 3 above, state the oxidizing agent and the reducing agent. 3

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Oxidising agent: Reducing agent: IONIC HALF EQUATIONS  Redox reactions involving a transfer of electrons can be split into two halves.  One half equation shows oxidation while the other half shows reduction.  In the reaction between sodium and chlorine, the two ionic half equations are: Na (s)  Na+ (s) + eoxidation – loss of electrons Cl2(g) + 2e  2Cl (s) reduction – gain of electrons  Please proceed to do exercise from: CHEMISTRY INSIGHTS, Pg. 328, Questions, Quest. 1-2. OXIDATION STATE  What is an oxidation state? The oxidation state is the charge of an atom of an element would have if it existed as an ion in a compound (even if it is covalently bonded).  To work out the oxidation state of an atom, we apply the following rules: 1) Elements are zero E.g. O2, He, Na, C are all zero. 2) Simple ions have an oxidation number = charge on the ion E.g. Na+ = +1, Al3+ = +3, S2- = -2 3) Hydrogen is +1 except when joined directly to metals (NaH, CaH2) 4) Oxygen is -2 except in peroxides where it is -1 (H2O2, Na2O2) 5) Compounds and radicals have their sum of oxidation numbers = total charge. E,g, SO2 S + 2O = 0 S + 2(-2) = 0 S = +4  Please proceed to do exercise from: WORKSHEET 1

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NAMES OF COMPOUNDS  The oxidation state of an element in a compound can be indicated by a Roman number. e.g. Manganese (IV) oxide, means the manganese has oxidation state of +4 in the compound.  Oxidation state are usually only given in the names of compounds where an element can have more than one oxidation state. e.g. Magnesium always has oxidation state of _______ in compounds so the name of MgSO4 is ________________________. Iron can have oxidation state of +2 or +3 in compounds, so the name of FeSO4 is ______________________________. 4) CHANGE OF OXIDATION STATE  Increase in oxidation state is _______________________.  Decrease in oxidation state is _______________________.

Oxidised: Oxidising agent:

Reduced: Reducing Agent:

 Please proceed to do exercise from: CHEMISTRY INSIGHTS, Pg. 333, Questions, Quest. 1-3. REDOX REACTION

UCTION

IDATION

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 Redox reaction is the combined process of oxidation and reduction. There can be NO oxidation without reduction and vice versa.  Please proceed to do exercise from: WORKSHEET 2 TEST FOR OXIDISING AND REDUCING AGENT

COMMON OXIDISING AND REDUCING AGENTS

 Please proceed to do exercise from: WORKSHEET 3 WORKSHEET 4

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WORKSHEET 1

WORKSHEET 2

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WORKSHEET 3

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WORKSHEET 4

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