A-level Chemistry: 3.2.5 Transition Metals Part 2
This flashcard set covers key concepts in redox titrations involving potassium manganate(VII) and iron(II) ions, including reaction conditions, indicators, and common errors. It also explores ligand substitution reactions and coordination chemistry of transition metal complexes, with emphasis on electron configurations and shape prediction limitations.
Ligand Substitution
If ligands are ____, they'll be a change in co-ordination number and shape
If ligands are different sizes, they'll be a change in co ordination number and shape
Key Terms
Ligand Substitution
If ligands are ____, they'll be a change in co-ordination number and shape
If ligands are different sizes, they'll be a change in co ordination number and shape
Ligand substitution reactions can be easily reversed. State when they can't be.
When new complex ion is more stable than old one
Give 2 examples of when ligand substitution reactions can't be easily reversed
If new ligands form stronger bonds with central metal ion than old ligands did
Multidentate ligands form more stable complex...
Explain why enthaply change for a ligand substitution reaction is usually very small
When ligand exchange reaction occurs, strength of co-ordinate bonds broken is often very similar to strength of new co-ordinate bonds being made
Why is this reaction considered irreversible when it is actually reversible?
Equilibrium lies so far to the right
[Ni(NH2CH2CH2NH2)3]2+ is much more stable than [Ni(NH3)6]2+
What explains why multidentate ligands always form much more stable complexes than monodenate ligands?
The chelate effect
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| Term | Definition |
|---|---|
Ligand Substitution If ligands are ____, they'll be a change in co-ordination number and shape | If ligands are different sizes, they'll be a change in co ordination number and shape |
Ligand substitution reactions can be easily reversed. State when they can't be. | When new complex ion is more stable than old one |
Give 2 examples of when ligand substitution reactions can't be easily reversed |
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Explain why enthaply change for a ligand substitution reaction is usually very small | When ligand exchange reaction occurs, strength of co-ordinate bonds broken is often very similar to strength of new co-ordinate bonds being made |
Why is this reaction considered irreversible when it is actually reversible? |
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What explains why multidentate ligands always form much more stable complexes than monodenate ligands? | The chelate effect |
Explain what the chelate effect is |
Difficult to reverse these reactions ∵ reversing = decrease in entropy |
Transition metals can exists in ___ ______ _____ | variable oxidation states |
Describe how vanadium(V) ions can be reduced | By adding them to zinc metal in an acidic solution |
Write the equation for when VO2+(aq) reacts with Zn(s) | |
Write the equation for when VO2+(aq) reacts with Zn(s) | |
Write the equation for when V3+(aq) reacts with Zn(s) | |
What does the redox potential of ion/atom tell you? | How easily the ion/atom is reduced to lower oxidation state (same as electrode potentials) |
Larger redox potential, less ion will be & more likely | Larger redox potential, less stable ion will be & more likely it's to be reduced |
Redox potential of an ion _ always be same as its standard electrode potential | WON'T |
What is the redox potential for a transition metal ion, when it changes from a higher to a lower oxidation state, influenced by? |
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Explain how different ligands affect redox potentials (& make them differ from standard electrode potentials) |
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Explain how different pHs affect redox potentials |
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What reaction does Tollens' reagent use to distinguish between aldehydes and ketones? State the equation | Tollens' reagent reacts with aldehydes to form a silver mirror, but does not react with ketones. Reaction equation: RCHO + 2[Ag(NH₃)₂]⁺ + 3OH⁻ → RCOO⁻ + 2Ag(s) + 4NH₃ + 2H₂O |
Describe how Tollens' reagent is prepared | Add ammonia solution to silver nitrate solution to form colourless solution containing complex ion [Ag(NH3)2]+ |
Describe what happens when aldehyde is added to Tollens' reagent |
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Write the equation for when Tollen's reagent reacts with an aldehyde (RCHO) | RCHO + 2[Ag(NH₃)₂]⁺ + 3OH⁻ → RCOO⁻ + 2Ag(s) + 4NH₃ + 2H₂O |
Titrations using Transition Element Ions are _ Titrations | Redox |
Titrations with Transition Metals What can you use the titrations to find out? | How much oxidising agent is needed to exactly react with a quantity of reducing agent |
Titrations with Transition Metals Suggest an oxidising agent you can use | aqueous potassium manganate(VII) |
Titrations with Transition Metals Suggest why aqueous potassium manganate(VII) is used as an oxidising agent |
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Titrations with Transition Metals Suggest 2 reducing agents you can use |
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Titrations with Transition Metals Describe a method |
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Why do transition metals and their compounds make good |
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What is the catalyst used in the Contact Process to make sulfuric acid? | Vanadium(V) oxide |
Why is vanadium(V) oxide used as a catalyst in the Contact Process? |
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Describe and state the 1st equation that occurs in the Contact Process. Include state symbols. | |
Describe and state the 2nd equation that occurs in the Contact Process. Include state symbols. | |
What are heterogenous catalyst? | A catalyst that's in a different phase from the reactants i.e. in a different physical state |
Where do reactions occur on in heterogenous catalysts? | Occur on on active sites on surface of heterogenous catalyst |
Explain why increasing SA of a catalyst increases the rate of a reaction | Increases no. of molecules that can react at same time |
What are often used to make the area of catalyst as large as possible? | Support mediums |
Explain how support mediums help to minimise the cost of a reaction? | ∵ only small coating of catalyst is needed to provide large SA |
Name 2 heterogeneous catalysts |
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State the overall equation for the Haber Process. Include the catalyst and state symbols. | N₂(g) + 3H₂(g) ⇌ 2NH₃(g) [Fe catalyst] |
State the overall equation for the Contact Process. Include the catalyst and state symbols. | 2SO₂(g) + O₂(g) ⇌ 2SO₃(g) [V₂O₅ catalyst] |
How do heterogenous catalyst work? | By adsorbing reactants onto active sites located on their surfaces |
Describe catalyst poisoning | Impurities (in reaction mixture) bind to catalyst's surface and block reactants from being adsorbed |
Explain how catalyst poisoning slows down the rate of a reaction | Catalyst poisoning reduces SA of catalyst available to reactants |
Explain why catalyst poisoning increases cost of chemical process |
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Name a substance that poisons the iron catalyst in the Haber Process | sulfur |
Explain how sulfur poisons the iron catalyst in the Haber Process |
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What are homogenous catalysts? | Catalysts that are in the same physical state as reactants |
Usually the homogenous catalyst is an _ catalyst for a reaction between 2 aqueous solutions | aqueous |
Describe how homogenous catalysts work | Work by combining with reactants to form an intermediate species which reacts to form products and re-form the catalyst |
Why does the enthalpy profile for a homogeneously catalysed reaction contain 2 humps? | 2 steps in reaction |
Activation energy needed to form intermediates is lower than… | that needed to make products directly from reactants |
______ reaction between iodide ions and peroxodisulfate (S2O82-) ions take place ________ | Redox reaction between iodide ions and peroxodisulfate (S2O82-) ions take place very slowly |
Why does the redox reaction between iodide ions and peroxodisulfate (S2O82-) ions take place very slowly? |
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State the equation for when iodide ions and peroxodisulfate ions react together | |
Name a catalyst that speeds up the reaction between iodide ions and peroxodisulfate ions | Fe2+ ions |
Explain why adding Fe2+ ions speeds up the reaction between iodide ions and peroxodisulfate ions | ∵ each stage of reaction involves a positive and a negative ion = no repulsion |
Describe and state the 1st equation that occurs when Fe2+ ions is added to iodide ions and peroxodisulfate ions. Include state symbols. | Fe2+ are oxidised to Fe3+ ions by S2O82- ions |
Describe and state the 2nd equation that occurs when Fe2+ ions is added to iodide ions and peroxodisulfate ions. Include state symbols. | Newly formed intermediate Fe3+ ions now easily oxidise the I- ions to iodine & catalyst is regenerated |
Mn2+ ions _ the reaction between C2O42– and MnO4– | Mn2+ ions autocatalyse the reaction between C2O42– and MnO4– |
Explain what it meant by an autocatalysis reaction |
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Write the overall equation for when Mn2+ ions autocatalyse the reaction between C2O42– and MnO4– | 2MnO₄⁻(aq) + 5C₂O₄²⁻(aq) + 16H⁺(aq) → 2Mn²⁺(aq) + 10CO₂(g) + 8H₂O(l) |
Describe and state the 1st equation that occurs when Mn2+ ions is added to C2O42– and MnO4–. Include state symbols. | Mn2+ oxidised to Mn3+ by MnO4- ions |
Describe and state the 2nd equation that occurs when Mn2+ ions is added to C2O42– and MnO4–. Include state symbols. | Mn3+ reduced to Mn2+ (re-form catalyst ions) by C2O42- ions |
Draw [Cr(en)3]3+ & state its shape and co-ordination number | Octahedral & 6 |
Draw [Co(en)2Cl2]+ & state its shape and co-ordination number | Octahedral & 6 |
Draw two geometric isomers of [NiCl2(H2O)4] | |
Draw two geometric isomers of square planar complex [PtCl2(NH3)2] | cis isomer = cisplatin |
Draw the two optical isomers of octahedral complex [Fe(C2O4)3]3- | |
State the charge of :CN- ligand | -1 |
State the charge of :OH- ligand | -1 |
Draw the structure of the ethanedioate ion, C2O42-. Explain how this ion is able to act as a ligand. (2) | lone pair(s) on O– / O |
Draw the structure of the 1,2-diaminoethane (en) | |
Give an example of complete ligand substitution when the co-ordination number and shape doesn't change. Include the colour change & shape. | [Cu(H₂O)₆]²⁺ (pale blue, octahedral) → [Cu(NH₃)₆]²⁺ (deep blue, octahedral) |
Give an example of incomplete ligand substitution when the co-ordination number and shape doesn't change. Include the colour change & shape. | [Cu(H₂O)₆]²⁺ (pale blue, octahedral) → [Cu(H₂O)₄(NH₃)₂]²⁺ (deep blue, octahedral) |
Give an example of complete ligand substitution when the co-ordination number and shape changes. Include the colour change & shape. | [Cu(H₂O)₆]²⁺ (pale blue, octahedral) → [CuCl₄]²⁻ (yellow-green, tetrahedral) |
Ligand Substitution Write an equation where a monodentate ligand replaces a monodentate ligand e.g. with [Fe(H2O)6]3+ with CN- | [Fe(H₂O)₆]³⁺ + 6CN⁻ → [Fe(CN)₆]³⁻ + 6H₂O |
Ligand Substitution Write an equation where a bidentate ligand replaces a monodentate ligand e.g. with [Cu(H2O)6]2+ and ethane-1,2-diamine | [Cu(H₂O)₆]²⁺ + 3en → [Cu(en)₃]²⁺ + 6H₂O |
Ligand Substitution Write an equation where a multidentate ligand (that's not a bidentate ligand) replaces a monodentate ligand e.g. with [Cr(NH3)6]3+ | [Cr(NH₃)₆]³⁺ + EDTA⁴⁻ → [Cr(EDTA)]⁻ + 6NH₃ |
When using potassium manganate(VII) in redox titrations with iron(II) ions it is essential that the reaction mixture is acidified. Explain why. (1) | ensures all MnO4- reacts to form Mn2+ / stop formation of MnO2 / becomes colourless |
Explain why an indicator is not needed in a redox titration with e.g. potassium manganate(VII) & iron(II) ions (1) | It's self-indicating |
Suggest one reason why the colour of potassium manganate(VII) can be a source of error when using a volumetric flask to prepare a standard solution (1) | Difficult to see meniscus |
State the equation for when dichromate(VI) ions react with iron(II) ions | Cr2O72- + 14H+ + 6Fe2+ → 2Cr3+ + 7H2O + 6Fe3+ |
Suggest one reason why electron pair repulsion theory cannot be used to predict the shape of the [CoCl4]2- ion (1) | Too many electrons in d sub-shell |
The redox reaction between acidified potassium manganate(VII) and sodium ethanedioate: Sketch a graph to show how the concentration of MnO4− ions varies with time in this reaction. Explain the shape of the graph. (4) |
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When the complex ion [Cu(NH3)4(H2O)2]2+ reacts with 1,2-diaminoethane, the enthaply change is appromimately zero. Suggest why. (2) |
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State the colour change for when iron(II) ethanedioate is titrated against potassium managante(VII) (burette) | Colourless to pale pink ∵ tiny excess of MnO4- (manganate(VII)) ions present |
Give 2 reasons why the use of a spectrometer is the most appropriate method for measuring the concentration of coloured ions (2) |
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Write an equation for the reaction that occurs between an aqueous solution of aluminium chloride and an excess of aqueous diaminoethane. Describe the appearance of the aluminium-containing reaction product. (3) | 2[Al(H2O)6]3+ + 3H2NCH2CH2NH2 → 2Al(H2O)3(OH)3 + 3[H3NCH2CH2NH3]2+ White precipitate |