Figure 3 shows some reactions of aqueous iron ions - AQA - A-Level Chemistry - Question 4 - 2019 - Paper 1
Question 4
Figure 3 shows some reactions of aqueous iron ions.
Solution containing Complex ion L
Reaction 1
Na2CO3(aq) → Precipitate J
Reaction 2
Concentrated HCl(aq)
React... show full transcript
Worked Solution & Example Answer:Figure 3 shows some reactions of aqueous iron ions - AQA - A-Level Chemistry - Question 4 - 2019 - Paper 1
Step 1
Give the formula of Precipitate J and state its colour.
Give an equation for Reaction 1.
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Answer
The formula of Precipitate J is [Fe(OH)3].
Its colour is brown.
Equation for Reaction 1:
2Fe3++3CO32−→2Fe(OH)3(s)+3H+
Step 2
Give the formula of L and an equation for Reaction 2.
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Answer
The formula of Complex ion L is [Fe(H2O)6]^{3+}.
Equation for Reaction 2:
[Fe(H2O)6]3++6HCl→[FeCl6]3−+6H2O
Step 3
Suggest a reagent for Reaction 3.
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Answer
A suitable reagent for Reaction 3 is zinc (Zn).
Step 4
Give the formula of Precipitate M and state its colour.
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Answer
The formula of Precipitate M is [Fe(OH)2].
Its colour is green.
Step 5
Transition metal complexes have different shapes and many show isomerism.
Describe the different shapes of complexes and show how they lead to different types of isomerism.
Use examples of complexes of cobalt(II) and platinum(II).
You should draw the structures of the examples chosen.
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Answer
The different shapes of coordination complexes primarily depend on the coordination number and the nature of the metal. For example:
Step 1: Shapes of complexes
Tetrahedral: Common for coordination number 4, e.g., [CoCl4]2−.
Octahedral: Common for coordination number 6, e.g., [Co(NH3)6]3+.
Step 2: Cis and trans isomerism (for E- or Z- geometry)
Cis-isomer: For example, in [Co(NH3)4Cl2]+, both chloride ions are adjacent.
Trans-isomer: In the same [Co(NH3)4Cl2]+, the chloride ions are on opposite sides.
Step 3: Optical isomerism
Optical isomerism: Occurs in octahedral complexes with bidentate ligands which create non-superimposable images. An example is [Co(en)3]3+ where en is ethylenediamine.
Diagrams should be drawn to illustrate each shape, showing the structure of each example.
