Redox Reaction

 

1. Oxidation occurs when there is a gain in oxygen, a loss of hydrogen, a loss of electron pr an increase in the oxidation number of a substance.
2. Reduction occurs when there is a loss of oxygen, a gain in hydrogen, a gain in electrons or a decrease in oxidation number of substance.
3. Oxidation and reduction take place simultaneously in a redox reaction
4. A substance that oxidizes another substance is called an oxidizing agent. Its is reduced in the redox reaction
5. A substance that reduces another substance is called a reducing agent. It is oxidized in the redox reaction
6. The oxidation number or oxidation state of an element take either a positive (+x) , a negative number (-x) or zero

 

Rusting as a Redox Reaction

 

1. Iron rust in the presence of both oxygen(air) and water
2. During the process of rusting , iron is converted into flaky brown coating (rust) which is hydrated iron (II) oxide, Fe₂O₃.3H₂O
3. Method to prevent rusting of iron include using a protective layer covering the iron surface, using a sacrificial metal and by forming alloys.

 

 

The Reactivity Series

 

1. Metal are placed in the order of their reactivity with oxygen in a list called the reactivity series of metals
2. Carbon is positioned between aluminium and zinc in the reactivity series
3. Hydrogen is positioned between zinc and iron in the reactivity series
4. metals are extracted from their ores using carbon or electrolysis of the molten metal ores

 

Redox reaction in electrolytic and chemical cells

 

1. In electrolysis cell, reduction occurs at the negative electrode (cathode) and oxidation occurs at the positive electrode (anode)
2. In a voltaic cell, oxidation occurs at the negative electrode (anode) and reduction occurs at the positive electrode ( cathode)

 

EXERCISE

 

1.       

a)     Describe how galvanizing iron can prevent rusting

b)     The table below shows the results of an experiment to study the reactivity of metals with oxygen

 

Metal	Colour of metal oxide formed		Intensity of flame
	Hot	Cold
Magnesium	White	White	Burned very rapidly with a bright flame
Lead	Brown	Yellow	Burned slowly with bright glow
Copper	Black	Black	Burned very slowly with faint glow

 

                                                                          i.      Predict the observation if zinc is used in the experiment

                                                                         ii.      Based on the observation, arrange the metals in increasing order of reactivity. Explain your answer

                                                                       iii.      Describe how you can carry out this experiment in the laboratory.

2.       

a)     Impure copper metal can be purified using electrolysis

                                                                          i.      Draw the set up of the apparatus for the electrolysis

                                                                         ii.      Explain how the purification of impure copper metal can be classified as a redox reaction.

b)     Explain the function of chlorine in the following reactions

                                                                          i.      The conversion of iron (II) ions Fe²⁺ to iron (III) ion Fe³⁺

                                                                         ii.      The displacement of iodine from potassium iodide solution

 

 

c)     The table above shows the methods used in the extract ion of aluminium and tin

                                                                          i.      Explain why aluminium cannot be extracted using the same method used in the extraction of tin

                                                                         ii.      Describe how tin can be extract by heating its oxide with carbon.

3.       

a)     By using a suitable example, explain the meaning of oxidation and reduction in term of

                                                                          i.      Electron transfer

                                                                         ii.      Changes in oxidation number

b)     Redox reaction can occur by transfer electron at a distance. By using a suitable example, describe an experiment to prove this statement. Your description should include the

                                                                          i.      Diagram

                                                                         ii.      Observation

                                                                       iii.      Ionic equation involved

                                                                      iv.      Reaction undergone by the reactants

4.       

a)     Neutralisation and double decomposition are not redox reaction. Explain this statement by using a suitable example

b)      

                                                                          i.      What is an electrochemical corrosion

                                                                         ii.      Give one example of an electrochemical corrosion

                                                                       iii.      State two ways to prevent iron from rusting. Explain how the prevention of rusting can occur

c)     A more reactive halogen is able to displace a less reactive halogen from it halide solution. Explain this statement by using a suitable example. Your description should include the

                                                                          i.      Procedure

                                                                         ii.      Observation

                                                                       iii.      Confirmation test for the formation of the halogen

                                                                      iv.      Half equation for the reaction

                                                                        v.      Oxidizing and reducing agent.