Topic 15: Transition Metals Flashcards by Elsie Rushworth

Define transition metals

D-block elements that form one or more stable ions with incompletely filled d-orbitals

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Give the characteristics of transition metals

hard solids
high melting and boiling temperatures
can act as catalysts
form coloured ions and compounds
form ions with different oxidation numbers
form ions with incompletely filled d-orbitals

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The relatively small size of a transition metals enables them to…

Attract electron-rich species more strongly including water molecules present in aq solutions

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Describe how the structure of a ligand is drawn

bonds are shown with arrow heads indicating dative bonds
whole structure drawn inside square brackets and the original charge of the ion is shown outside the brackets

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What is the coordination number

The total number of dative bonds around the metal ion

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Define ligand

A species that uses a lone pair of electrons to form a dative bind with a metal ion

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Define complex

A species containing a metal ion joined to ligands

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Define complex ion

A complex with an overall positive or negative charge

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Explain how complexes are named

In order:
- number of ligands eg. hexa
- name of ligand eg. aqua
- name of metal ion eg. iron
- oxidation number of the metal ion eg. (II)

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Give the stock answer for the following question:
Explain why the solution is coloured

Water ligand causes 3d orbital to split into 2 energy levels
Electrons in the lower energy level absorb energy from the visible spectrum and are executed to a higher energy level
(**) light is transmitted as its complementary colour is absorbed

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Give 2 examples of a square planar complex

xenon tetrafluoride XeF4
cis-platin

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Describe the cis and trans isomers of cis-platin

Cis = identical ligands are next to eachother, Trans = opposite

Cis-platin consists of a platinum (II) ion, two ammonia ligands and two chloride ion ligands

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Explain briefly the anti-cancer action of cis-platin

all cells including cancer cells contain DNA
during cell division the 2 strands of DNA must separate from eachother to form more DNA
the structure of cis-platin enables it to form a bond between the 2 strands of DNA, preventing them from separating & so prevents the cancer cells from dividing

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Define monodentate, bidentate and multidentate ligands

Monodentate ligands are ones that form one dative bond with a metal ion
Bidentate ligands form 2 dative binds with a metal ion
Multidentate ligands form several dative bonds with a metal ion

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What is the most common bidentate ligand

NH2CH2CH2NH2 (1,2 diaminoethane) sometimes abbreviated to en

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What is the most common multidentate ligand

EDTA (6 dative bonds)

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What is the effect on the stability of a complex when a ligand exchange reaction takes place ?

If the total number of species (ligands) increases, the system becomes more disordered
As a result there is an increase in △S(system)
Formation of products is favoured due to their increased stability compared to reactants

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How does the oxygen molecule act as a ligand in haemoglobin

When haemoglobin collects oxygen, oxygen uses one of its lone pairs of electrons to form a dative bond with one of the Fe2+ ions

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Explain the effect of carbon monoxide on haemoglobin

Carbon monoxide has a lone pair of electrons on its carbon atom that enables it to act as a ligand
The strength of the dative bond between oxygen and haemoglobin < strength of dative bond between carbon monoxide and haemoglobin
Therefore any carbon monoxide breathed in is likely to replace the oxygen in a ligand substitution reaction
The oxygen carrying capacity of the blood is reduced as the dative bond is so strong that it does not break easily

What are the 4 main types of reaction that can occur with transition metal ions causing a change in colour

redox : change in oxidation number of metal cation
acid-base reaction : one or more of the ligands loses/gains hydrogen
ligand exchange : substitution of one or more of the ligands around the transition metal ion
coordination number change : number of ligands changes

Give the equation for the change in coordination number reaction Cu2+ ion with concentrated HCl
State observations

[Cu(H2O)6]2+. +. 4Cl- ——> [Cu(Cl)4]2- +. 6H2O

Acid is added slowly and continuously - colour gradually changes from blue to green to yellow

Give the equations and colour changes for reaction of Cr3+ ion with OH- and excess OH-

With OH- : [Cr(H2O)6]3+. +. 3OH- ——>. [Cr(H2O)3(OH)3]. +. 3H2O
violet solution - green ppt

With excess OH- : [Cr(H2O)3(OH)3]. + OH- ——>. [Cr(H2O)2(OH)4]- +. H2O
green ppt - green solution

Give the equations and colour changes for reaction of Fe2+ ion with OH- and excess OH-

With OH- : [Fe(H2O)6]2+. +. 2OH- ——> [Fe(H2O)4(OH)2] +. 2H2O
pale green solution - green ppt

With excess OH- : no further change

Give the equations and colour changes for reaction of Fe3+ ion with OH- and excess OH-

With OH- : [Fe(H2O)6]3+. +. 3OH- ——> [Fe(H2O)3(OH)3] +. 3H2O
yellow-brown solution - brown ppt

With excess OH- : no further change

Give the equations and colour changes for reaction of Co2+ ion with OH- and excess OH- What happens upon standing ?

With OH- : [Co(H2O)6]2+. +. 2OH- ——> [Co(H2O)4(OH)2] +. 2H2O pink solution - blue ppt Upon standing : colour of ppt gradually changes pink With excess OH- : no further change

Give the equations and colour changes for reaction of Cu2+ ion with OH- and excess OH-

With OH- : [Cu(H2O)6]2+. +. 2OH- ——> [Cu(H2O)4(OH)2] +. 2H2O pale blue solution - blue ppt With excess OH- : no further change

Give the equations and colour changes for reaction of Cr3+ ion with NH3 and excess NH3

With NH3 : [Cr(H2O)6]3+. +. 3NH3 ——> [Cr(H2O)3(OH)3] +. 3NH4+ violet solution - green ppt With excess NH3 : [Cr(H2O)3(OH)3] +. 6NH3. —-> [Cr(NH3)6]3+ +. 3H2O. +. 3OH- green ppt - purple solution

Give the equations and colour changes for reaction of Fe2+ ion with NH3 and excess NH3 what happens upon standing ?

With NH3 : [Fe(H2O)6]2+. +. 2NH3 ——> [Fe(H2O)4(OH)2] +. 2NH4+ pale green solution - green ppt Upon standing : colour of green ppt gradually changes to brown as o2 from atmosphere causes oxidation, forming [Fe(H2O)3(OH3)] With excess NH3 : No further change

Give the equations and colour changes for reaction of Fe3+ ion with NH3 and excess NH3

With NH3 : [Fe(H2O)6]3+. +. 3NH3 ——> [Fe(H2O)3(OH)3] +. 3NH4+ yellow-brown solution - brown ppt With excess NH3 : No further change

Give the equations and colour changes for reaction of Co2+ ion with NH3 and excess NH3 What happens upon standing

With NH3 : [Co(H2O)6]2+. +. 2NH3 ——> [Co(H2O)4(OH)2] +. 2NH4+ pink solution - blue ppt With excess NH3 : [Co(H2O)4(OH)2]. +. 6NH3 ——> [Co(NH3)6]2+. +. 4H2O. +. 2OH- blue ppt - brown solution Upon standing the brown solution changes colour to yellow because of the oxidation by o2 in the atmosphere. [Co(NH3)6]3+ is formed (ie. oxidation number changes from +2 to +3)

Give the equations and colour changes for reaction of Cu2+ ion with NH3 and excess NH3

With NH3 : [Cu(H2O)6]2+. +. 2NH3 ——> [Cu(H2O)4(OH)2] +. 2NH4+ pale blue solution - blue ppt With excess NH3 : [Cu(H2O)4(OH)2]. +. 4NH3 ——> [Cu(NH3)4(H2O)2]2+. +. 2H2O. +. 2OH- blue ppt - dark blue solution

Give the equation for the change in coordination number reaction Co2+ ion with concentrated HCl State observations

[Co(H2O)6]2+. +. 4Cl- ——> [Co(Cl)4]2- +. 6H2O Pink solution gradually changes to blue

Give the equation for the oxidation of a Cr3+ ion State conditions and observations

Providing solutions are alkaline, oxidation is achieved by the addition of hydrogen peroxide (H2O2) 2[Cr(OH)6]3- + 3H2O2. ——>. 2CrO4 2- +. 2OH- +. 8H2O Solution changes from green to yellow

Describe and explain the reaction of chromate (VI) ions in acidic conditions

2CrO4^2- + 2H+ ⇌ Cr2O7^2- + H2O In acidic conditions the dichromate (VI) ion is more stable than the chromate (VI) ion Colour change from yellow to orange

Describe and explain the stages in the reduction of dichromate(VI) ions

Zinc metal is added to an acidic solution containing dichromate(VI) ions Reduction reactions occur in which the oxidation number of chromium decreases first to +3 then to +2 1st stage : colour change orange - green Cr2O7^2- +. 14H+ +. 3Zn. —-> 2Cr^3+. +. 7H2O. +. 3Zn^2+ 2nd stage: colour change green - blue 2Cr^3+. +. Zn. —->. 2Cr^2+. +. Zn^2+

Give the colour of an aq solution of vanadium (II) : V^2+

Purple

Give the colour of an aq solution of vanadium (III) : V^3+

Green

Give the colour of an aq solution of oxovanadium (IV) : VO^2+

Blue

Give the colour of an aq solution of dioxovanadium (IV) : VO2^+

Yellow

Give the 2 parts of the contact process

Part 1 : sulfur dioxide adsorbs onto the vanadium (V) oxide and a redox reaction occurs V2O5 + SO2 —-> V2O4 + SO3 Note: oxidation number of vanadium decreases from +5 to +4 and the SO3 then desorbs Part 2: oxygen reacts with the V2O4 on the surface of the catalyst and another redox reaction occurs V2O4 + 1/2O2 —-> V2O5 Note: original catalyst is regenerated as the oxidation number increases from +4 to +5

How does carbon monoxide form in exhaust fumes

The incomplete combustion of hydrocarbon fuels

Define autocatalysis

Occurs when a reaction product acts as a catalyst for the reaction

Give a reason why the reaction of an S2O8^2- ion with iodide ions is very slow at room temp

Two reactant ions are natively charged so repel eachother

Explain the role of Fe2+ ions in catalysing the reaction between S2O8^2- ions and I- ions

Step 1 : the Fe2+ ions are not repelled by the S2O8^2- ions as they have opposite charge S2O8^2- +. 2Fe^2+. ——> **2SO4^2-** +. 2Fe^3+ Step 2: the Fe^3+ ions formed in step 1 can now react with the I- ions 2Fe^3+. +. 2I- —->. 2Fe^2+ + I2 Steps can repeat continuously

Explain the role of Mn2+ ions in autocatalysing the reaction between MnO4^- and C2O4^2- ions

2MnO4^- +. 5C2O4^2- +. 16H+ ——> 2Mn^2+ +. 5CO2 +. 8H2O Both reacting species are negatively charged so reaction is slow. However as more potassium manganate(VII) solution is added the reaction increases as Mn2+ ions are formed which acts as a catalyst for the reaction explaining why the rate of reaction increases as titration proceeds