This is an extensive and detailed set of notes for each Year 12 Module (5, 6, 7, 8), complete with diagrams and explanations to guide and facilitate your understanding of the Year 12 Chemistry Syllabus. The notes are structured according to the syllabus so that each dot point is answered in depth.
Static and Dynamic Equilibrium
Inquiry Question: What happens when chemical
reactions do not go through to completion?
● Conduct practical investigations to analyse the reversibility of
chemical reactions, for example:
● Reversible reactions can react both ways - the products which are formed can
react again to form the reactants
○ If a reverse reaction is possible, it will have the exact opposite
thermodynamic properties
○ ΔH, ΔS, and ΔG values will be the negative of its forward reaction value
■ Eg N2(g) + 3H2(g) ⇌ 2NH3(g). ΔH = -46 kJ mol-1
● Dynamic equilibrium is a type of reversible reaction where forward and reverse
reactions occur simultaneously at the same rate
○ Not all reactions are reversible; some reactions (e.g. combustion reactions)
are irreversible
, - Cobalt(II) chloride hydrated and dehydrated
Aim: analyse the reversibility of the dehydration of cobalt (II) chloride hexahydrate
Materials:
● 5g cobalt (II) chloride hexahydrate [CoCl2・6H2O (s)]
○ CoCl2・6H2O (s) has an ionic lattice structure
○ There are 6 H2O molecules per CoCl2 molecule in the ionic lattice - they are
called waters of crystallisation
● Evaporating dish
● Gauze mat
● Bunsen burner
● Demineralised water
Method:
1. Add 5.00g of cobalt (II) chloride hexahydrate to an evaporating dish and set it on
top of a gauze mat
2. Gently heat the cobalt (II) chloride hexahydrate with a Bunsen Burner and observe
the two colour changes that take place
3. When there is no further colour change after ~5 minutes, add ~5 ml of demineralised
water to re-dissolve the salt that remains in the evaporating dish. Observe the
colour of the dissolved substance
4. Evaporate the solution to dryness and observe the colour changes
Observations:
● CoCl2・6H2O (s) ⇌ CoCl2・2H2O (s) + 4H2O (l)
○ CoCl2・6H2O (s) is a pink hexahydrate
○ CoCl2・2H2O (s) is a purple dihydrate
○ The waters of crystallisation (4H2O) evaporate gradually when heated
● CoCl2・2H2O (s) ⇌ CoCl2 (s) + 2H2O (l)
○ CoCl2 (s) is a blue anhydrous cobalt (II) chloride
● If water is added to CoCl2 (s), CoCl2・6H2O (aq) will be re-formed as water is
absorbed into the structure of CoCl2・6H2O (aq)
○ The blue solid will become a pink solution (aqueous)
● If the water is evaporated, the pink solution will become a pink solid CoCl2・6H2O (s)
○ Water can be evaporated naturally, without heat
○ Water can also be evaporated using gentle heat (~50-60°C), as long as the
water hydrating the anhydrous cobalt (II) chloride is not evaporated
■ Gentle heat can be used to turn the solution into a solid, as long as the
water hydrating the anhydrous cobalt (II) chloride is not evaporated
● The reaction is reversible but does not represent a true dynamic chemical
equilibrium as both reactions do not occur simultaneously
,Conclusion: The reversibility of the dehydration of hydrated cobalt (II) chloride was
observed.
- Iron(III) nitrate and potassium thiocyanate
Aim: show the reversibility of the reaction between iron (III) nitrate and potassium
thiocyanate
Materials:
● Ice bath
● Warm water bath
● Demineralised water
● Measuring cylinder
● 2 mL 0.1 mol L-1 iron (III) nitrate solution
● 2 mL 0.1 mol L-1 potassium thiocyanate solution
● Test tube rack
● Dropper bottles of 0.5 mol L-1 iron (III) nitrate and potassium thiocyanate
● 5 identical test tubes (labelled 1-5)
Method:
1. Pour 2 mL of 0.1 mol L-1 iron (III) nitrate into the measuring cylinder, and note its
colour.
2. Dilute it with demineralised water to make up a volume of 20 mL.
3. Hold 2 mL of potassium thiocyanate to the solution, and note its colour.
4. Divide the mixture between 5 test tubes, with approximately the same amount per
tube. Leave 1 test tube unchanged.
5. Add a few drops of 0.5 mol L-1 of iron (III) nitrate to test tube 2, and observe any
changes.
6. Add a few drops of 0.5 mol L-1 of potassium thiocyanate to test tube 3, and observe
any changes.
7. Place test tube 4 in the warm water bath and observe any changes.
8. Place test tube 5 in the warm water bath and observe any changes.
Observations:
● Fe(NO3)3 is initially slightly a pale-orange/yellow colour
● KSCN is colourless
● The mixture formed is blood-red
○ Fe3+ (aq) + SCN- (aq) ⇌ FeSCN2+ (aq) ΔH<0
Tube Change imposed Observations Explanation
1 None Solution was blood-red Mixture is blood-red
2 Add extra iron (III) Solution turned pale orange, Equilibrium shifts right (LCP)
, nitrate then became blood red
3 Add extra Solution became a darker Equilibrium shifts right (LCP)
potassium blood-red
thiocyanate
4 Mixture is warmed Solution lightened to become Equilibrium shifts left to favour
very pale orange endothermic reaction
5 Mixture is cooled Solution becomes a darker Equilibrium shifts right to favour
blood-red colour exothermic reaction
Conclusion: The reversibility of the iron (III) thiocyanate equilibrium was proved as the
system reacted to mitigate changes made to the equilibrium.
- Burning magnesium
Aim: investigate the reversibility in the combustion of magnesium
Materials:
● Magnesium strip
● Crucible and lid
● Bunsen burner
● Heat mat
● Tripod
● Pipeclay triangle
● Test tube
● Ice bath
Method:
1. Set up as shown in the diagram
2. Observe the changes to the magnesium strip as it is heated
3. Collect the remaining solid and place it in a test tube. Place the test tube in an ice
bath and observe any changes
➔ The ice bath cools the solid so that reversibility can be tested
Observations:
● No changes occur when the solid is cooled in an ice bath
● 2Mg (s) + O2 (g) → 2MgO (s)
○ The combustion of magnesium produces a white solid and a bright light
○ A single arrow is used to indicate that the reaction goes to completion, and
hence is irreversible
Conclusion: The fact that cooling does not result in the formation of magnesium suggests
that the combustion of magnesium is irreversible.
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