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)
[Fe(H2... 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.
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Answer
The formula of Precipitate J is [ Fe(OH)_3 ] and its colour is brown.
The equation for Reaction 1 can be written as:
[ 2Fe^{3+} + 3Na_2CO_3 \rightarrow 2Fe(OH)_3 + 3Na_2 ]
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(H_2O)_6]^{3+} ].
The equation for Reaction 2 is:
[ [Fe(H_2O)_6]^{3+} + 6HCl \rightarrow [FeCl_6]^{3-} + 6H_2O ]
Step 3
Suggest a reagent for Reaction 3.
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Answer
A suitable reagent for Reaction 3 is potassium iodide (KI) or concentrated HCl.
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 ] and its colour is green.
Step 5
Describe the different shapes of complexes and show how they lead to different types of isomerism.
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Answer
Different Shapes of Transition Metal Complexes
Transition metal complexes can adopt various geometries, including octahedral and tetrahedral shapes. The geometry influences the possibility of isomers due to the arrangement of ligands around the central metal ion.
Stage 1: Shapes
Octahedral: Common for complexes with coordination number 6. Example: [ [Co(NH_3)_6]^{3+} ].
Tetrahedral: Common for complexes with coordination number 4. Example: [ [CoCl_4]^{2-} ].
Stage 2: Cis-Trans Isomerism
This type occurs in octahedral complexes.
Cis Isomers: Ligands adjacent to each other on the metal center, e.g., [ [Co(NH_3)_2Cl_2]^{+} ].
Trans Isomers: Ligands opposite each other, e.g., [ [Co(NH_3)_2Cl_2]^{+} ].
Stage 3: Optical Isomerism
Optical isomerism arises when a complex cannot be superimposed on its mirror image.
For example:
Octahedral: The complex [ [Co(NH_3)_3(Cl)_3] ] can exist in chiral forms.
These different geometries and arrangements of ligands lead to unique properties and reactivity in coordination chemistry.
