RedRedoxox Reactions Reactions

Chemical ReactionsChemical Reactions

There are 3 major classes of There are 3 major classes of chemical reaction:chemical reaction:

1. Precipitation1. Precipitation

2. Acid-base2. Acid-base

3. Redox3. Redox

OxidationOxidation

Refers to the gain of oxygen in a Refers to the gain of oxygen in a chemical reactionchemical reaction

EXAMPLE:EXAMPLE:

Iron + oxygen Iron + oxygen Iron(II) oxide

Write the chemical equation (unbalanced)

Fe + O2 FeO

The iron has gained oxygen and has been oxidised

ReductionReduction

Is the opposite of oxidationIs the opposite of oxidation This means that it involves the lose This means that it involves the lose

of oxygenof oxygenWrite a chemical equation for the reduction of calcium oxide.

Balance the equation

CaO Ca + O22 2

Redox reactionsRedox reactions

Write a similar equation for the reaction of zinc and iron oxide.

Label the oxidation and reaction steps

Whenever a chemical is oxidised, Whenever a chemical is oxidised, another chemical must be reduced, and another chemical must be reduced, and vise veravise vera

EXAMPLE:EXAMPLE: MgMg + + CuOCuO MgOMgO + + CuCu

Introducing electronsIntroducing electrons

MgMg + + CuOCuO MgOMgO + + CuCu

The oxidation and reduction steps can The oxidation and reduction steps can be written out separately:be written out separately:

Mg MgOMg MgO CuO CuCuO Cu

Re-write the above two steps, but add charges to the ions involved

OXIDATION

REDUCTION

Mg2+O2-Cu2+O2

-

In the oxidation step:In the oxidation step:

Mg + OMg + O2 2 Mg Mg2+2+OO2-2-

The magnesium The magnesium atomsatoms have turned into have turned into magnesium magnesium ionsions

Have they gained or lost electrons?Have they gained or lost electrons?OXIDATION IS ALWAYS LOSS of OXIDATION IS ALWAYS LOSS of

electronselectronsO.I.L.O.I.L.

Where have the electrons gone to?Where have the electrons gone to?

They have been taken by the copper:They have been taken by the copper:

CuCu2+2+OO2-2- Cu Cu

The copper has turned from ions into The copper has turned from ions into atomsatoms2+ NEUTRAL+ 2-

Cu2+ + 2e Cu

REDUCTION IS ALWAYS GAIN of REDUCTION IS ALWAYS GAIN of electrons electrons

R.I.G.R.I.G.

PracticePractice

Write similar Write similar ion-electron equationsion-electron equations for: for:

Calcium ions turning into calcium atomsCalcium ions turning into calcium atoms

Sodium ions turning into sodium atomsSodium ions turning into sodium atoms

Aluminium ions turning into aluminium Aluminium ions turning into aluminium atomsatoms

Potassium atoms turning into potassium Potassium atoms turning into potassium ionsions

Nickel atoms turning into nickel(II) ionsNickel atoms turning into nickel(II) ions

All of these REDUCTIONS can be found in the data booklet

Writing ion-electron Writing ion-electron equationsequations

All reductions are found in data All reductions are found in data bookletbooklet

To write the oxidation, To write the oxidation, reversereverse the the equationequation

Cu2+ + 2e Cu

Cu Cu2+ + 2e

Both sides of the equation should Both sides of the equation should be neutral when the charges are be neutral when the charges are added togetheradded together REMEMBER: REMEMBER: OIL RIGOIL RIG

ProblemsProblems

1.1. Look at the following equation:Look at the following equation:

Zn + AgZn + Ag22O ZnO + O ZnO + AgAg

(a)(a) Which chemical is being oxidised?Which chemical is being oxidised?

(b)(b) Write an ion-electron equation for the Write an ion-electron equation for the oxidation step.oxidation step.

(c)(c) Write an ion-electron equation for the Write an ion-electron equation for the reduction step.reduction step.

2.2. Assessment tests 10.3 and 10.4 Assessment tests 10.3 and 10.4