Revision on redox ==july=2011=part 1

Part 1 seminar camp

science= chemistry

Seminar part 1) SPM 20099 (a) Diagram 9 shows the apparatus and observations for a redox reaction between iron(III) chloride solution and a metal.

At the beginning of the experiment After 30 minutes

Diagram 9

Based on the observations shown in Diagram 9, suggest a suitable metal to be used in this experiment.

Zinc/ magnesium

Based on the observations shown in Diagram 9, Predict the ion present in the green solution

iron (II) ion

•The change in oxidation no for both the reactants

•Change in Ox no of iron is from +3 to +2 ( iron(III) to iron (II) )•Change in Ox no of metal zinc is from 0 to +2 ( zinc to zinc ion)

Iron(III) chloride

The type of reaction that has occurred to each reactant

•Iron(III) ion undergoes reduction

( ox no decrease from +3 to +2)

•Metal atom undergoes oxidation

(Ox no increase from 0 to +2)

Iron(III) chloride

The role of each reactant in the redox reaction

•Iron(III) ion is an oxidising agent

Because it has oxidised zinc to zinc ion

•Metal is a reducing agent

Because it has reduced iron(III) ion to iron(II) ion

Iron(III) chloride

Half -equations involved in redox reaction

•For iron (III) chloride,

Fe 3+ + e Fe 2+

•For metal zinc,

Zn Zn 2+ + 2e

Iron(III) chloride

  (b) iodide ions are good reducing agent.

You are given the following apparatus:U-tube, galvanometer, connecting wires, stopper, dropper, carbon electrodes and retort stand with clamps.Suggest a suitable chemical and describe an experiment to verify the above statement using the given apparatus.

Chemicals1. Oxidising agent such as Acidified KMnO4 //

Acidified K2Cr2O7 //Bromine water// chlorine

water // iron (III) chloride solution 2. Sulphuric acid as electrolyte3. Potassium iodide solution

Procedure1. Pour sulphuric acid into U tube untill it reach about 5 cm from the mouth of the U-tube2. Add potassium iodide solution in one arm of the U tube

3. Add acidified KMnO4 / or any oxidising agent into the other arm4.The solutions are added slowly so that they do not mix5. Dip the graphite electrodes into the two separate solutions and connect it to the galvanometer

After 10 minutes,

The colour of KMnO4 changesfrom purple to colourless

MnO4- ion is reduced to

Mn 2+ ion

• Colour of potassium iodide solution change to dark brown

• Iodide ion released electrons to form iodine

• 2I - I2 + 2e• Iodide ions has reduced acidified

potassium manganate (VII) to manganese ions

• MnO 4 2- +8H + + 5e Mn 2+ + 4H2O

Part 1)SPM 20089(a) A metal M reacts with oxygen to form an oxide. The oxide is very soluble in water to produce an alkaline solution.Suggest the identity of metal M and describe an observation when the metal you have named reacts with oxygen, write the half-equations for oxidation and reduction for the reaction.

[4 marks]

• Metal M is sodium/ potassium / lithium

• Metal sodium burns brightly with a yellow flame in oxygen to form

white fumes which becomes white

solid when cooled at room temperature

eNaNa

oxidationequationHalf ::

2

2 24

::

OeO

reductionequationHalf

(b) Diagram 9 shows an apparatus set-up to investigate the effect of two different metals, X and Y on the rusting of iron, Fe.

The result of this experiment after three days is shown in Table 9.

Pair of metals

Observation

Fe, X Dark blue colour

Fe, Y No change

Based on Table 9, suggest the identity of metals, X and Y. Give two reasons for each of your choices [6 marks]

• Dark blue colour shows presence of iron(II) ions.

• Means iron nail has rusted• Metal X is copper/ any metals

below iron in ECS• Because copper is less electropositive than iron • So, copper will encourage iron to

rust

Based on Table 9, suggest the identity of metals, X and Y. Give two reasons for each of your choices [6 marks]• No change means iron nail has

not rusted• Metal Y is zinc/Magnesium • Because zinc/magnesium is more

electropositive than iron • So, zinc/magnesium will protect

iron from rusting

• Seminar Part 1) SPM 2008• 9(C) Iron(II) ions can be converted to

iron(III) ions and iron(III) ions can be converted back to iron(II) ions. By using a named metal as a reducing agent and a named halogen as an oxidising agent, describe briefly how you would carry out these two conversions.

• Describe a test to show that each conversion has taken place.

[10 marks]

CHANGING OF Fe2+ TO Fe3+

CHANGING OF Fe2+ TO Fe3+

1)Pour 2 cm3 of FeSO4 solution into a test tube.

2)Add chlorine water drop by drop until no further changes.

3)Warm the test tube gently.

4)Add sodium hydroxide solution in excess into the test tube.

CHANGING OF Fe2+ TO Fe3+

1) If Fe 3+ present, the colour of the solution turn brown precipitate.

OXIDISING AGENT : CHLORINE WATER

CHANGING OF Fe3+ TO Fe2+

CHANGING OF Fe3+ TO Fe2+

1)Pour 2 cm3 of FeCl3 solution into a test tube.

2)Add half spatula of Zinc powder into the solution until no further changes.

3)Warm the mixture.

CHANGING OF Fe3+ TO Fe2+

1)Filter the mixture using filter funnel and filter paper to remove the excess zinc.

2)The filtrate is then added with excess NaOH solution. If Fe 2+ present, green precipitate is observed.

REDUCING AGENT : Zn metal

End of part 1