Transition metal reactions Flashcards
Reactions of inorganic compounds in aqueous solution
What is a lewis acid?
a lewis acid is an electron pair acceptor
What is a lewis base?
a lewis base is an electron pair donor
Give an example of a lewis acid and lewis base reaction? Describe what happens between these two acid and bases?
- reaction of ammonia (NH3) and Boron Trifluoride (BF3)
- Ammonia donates a pair of electrons to the boron atom, forming a coordinate bond
- NH3 is acting as a lewis base, BF3 is acting as a lewis acid.
How is the hydronium ion formed?
What is acting as a lewis base and what is acting as a lewis acid?
- H2O + H+ —-> H3O+
- the water molecule is donating an electron pair to the hydrogen ion - lewis base
- The hydrogen ion is accepting a lone pair of electrons, so is acting as a lewis acid
How is Aluminium tetrachloride ion formed?
- Aluminium chloride can combine with A chloride ion to form AlCl4-
- AlCl3 + Cl- –> AlCl4-
- aluminium chloride is accepting an electron pair - lewis acid
- chloride ion is donating an electron pair - lewis base
What is formed, when transition metals dissolve in water?
when transition metals dissolve in water, the water molecules form coordinate bonds with the metal ions
- a metal aqua complex ions is formed (hexaaqua metal complex ion)
What is the charge on the ion?
the charge on the ion is either 2+ or 3+
Describe bonding in an hexaaqua metal complex ion?
- each water ligand donates a pair of electrons, therefore acts as a lewis base
- the mtal ion accepts the pair of electrons - acts as a lewis acid
What is a ligand?
All ligands are…?
A ligand is a water molecule or ion which donates a pair of electrons to a metal ion to form a coordinate bond
(All ligands are lewis bases - all have lone pair of electrons which they donate to a transition metal ion)
What is a complex?
a complex is a transition metal ion with several ligands coordinately bonded to it
What is the coordination number?
The coordination number of the coordinate bonds formed around a transition metal
(In this case hexaaqua metal ions have a coordination number of 6)
What is the shape of Hexaaqua metal complexes?
Octahedral shape
What is the charge on the complex ion the same as?
the charge ion the transition metal, as water molecules are neutral
(charge is either 2+ and 3+)
What are the Transition meta complexes that have a +2 charge?
- [Fe(H2O)6]2+
- [Cu(H2O)6]2+
- [Co(H2O)6]2+
What are the main transition metal ions which have a +3 charge?
-[Fe(H2O)6]3+
- [Al(H2O)6]3+
- [Cr(H2O)6]3+
Reactions of HexaAqua Metal complex ions
What are the four different examples of Metal ions that dissolve in water to form Hexaaqua Metal ion complexes (that we need to know)?
What is the colour of each solution?
- Copper (II) sulphate CuSO4 (aq) - Blue solution
- Iron (II) sulphate FeSO4 (aq) - pale green solution
- Iron (II) sulphate Fe(SO3)4 (aq) - Yellow solution
- Aluminium sulphate - Al2(SO4)3 (aq) - Colourless solution
What is the observation of each of these hexaaqua complexes with A few drops of NaOH and Excess NaOH (aq)?
- Copper (II) sulphate CuSO4 (aq) Few drops = Blue precipitate Excess = Blue precipitate (does not dissolve in excess)
- Iron (II) sulphate FeSO4 (aq) - Few drops = Green precipitate (turns brown on oxidation) Excess = Green precipitate (does not dissolve in excess)
- Iron (II) sulphate Fe(SO3)4 (aq) - Few drops = Brown precipitate Excess = Brown precipitate (does not dissolve in excess)
- Aluminium sulphate - Al2(SO4)3 (aq) - Few drops = white precipitate Excess = Colourless solution formed (dissolves in excess)
State the products and what occurs between the reaction between Hexaaqua metal ions with a few drops of Sodium hydroxide (NaOH)?
What is formed?
- All Hexa Aqua metal ions react with a few drops of NaOH
- They all form Metal hydroxide precipitate
Metal ions with a +2 charge form..?
[M(OH)2(H2O)4] (s) (+ 2H2O)
Metal ions with a +2 charge form..?
[M(OH)3(H2O)3] (S) (+ 3H20)
Write equations for the reactions of the following metal ion complexes with A FEW drops of SODIUM HYDROXIDE (NaOH):
1. [Cu(H2O)6]2+
2. [Fe(H2O)6]2+
3. [Fe(H2O)6]3+
4. [Al(H2O)6]3+
- [Cu(H2O)6]2+ + 2OH- —-> [Cu(OH)2(H2O)4] (s) + 2H2O (l)
- [Fe(H2O)6]2+ + 2OH- –> [Fe(OH)2(H2O)4] (S) + 2H2O (l)
- [Fe(H2O)6]3+ + 3OH- —–> [Fe(OH)3(H2O)3] (s) + 3H2O (l)
- [Al(H2O)6]3+ + 3OH- —-> [Al(OH)3(H2O)3] (s) + 3H2O (l)
Describe the reaction of metal ion solutions with excess of Sodium hydroxide (NaOH)?
What is formed?
- All metal (II) hydroxide precipitates do NOT dissolve in excess NaOH
- All Metal (III) hydroxides precipitates DO dissolve in Excess NaOH, except [Fe(OH)3(H2O)3
Write an equation to show how the reaction when Excess Sodium Hydroxide (NaOH) is added to:
1. CuSO4 (aq)
2. FeSO4 (aq)
3. Fe2(SO3)4 (aq)
4. AlCl3 (aq)
- does not dissolve in exess NaOH, so forms only a metal (II) hydroxide precipitate [Cu(H2O)6]2+ + 2OH- —-> [Cu(OH)2(H2O)4] (s) + 2H2O (l)
- does not dissolve in exess NaOH, so forms only a metal (II) hydroxide precipitate [Fe(H2O)6]2+ + 2OH- –> [Fe(OH)2(H2O)4] (S) + 2H2O (l)
- Does not dissolve in excess NaOH, so forms only a metal (III) hydroxide precipitate [Fe(H2O)6]3+ + 3OH- —–> [Fe(OH)3(H2O)3] (s) + 3H2O (l)
- ([Al(H2O)6]3+ + 3OH- —-> [Al(OH)3(H2O)3] (s) + 3H2O (l)) - few drops of NaOH
- [Al(OH)3(H2O)3] formed dissolves in excess NaOH so forms [Al(OH)3(H2O)3] (s) + oh- (aq) –> [Al(OH)4] (aq) + 3H2O (l)
Reactions With Ammonia NH3 (aq)
What is formed when ammonia is added to water?
Write a word equation to show this reaction?
an alkaline solution is formed
NH3 (g) + H2O (l) ⇌ NH4+ (aq) + OH- (aq)
Why is the results the same as when we add a few drops of NaOH and NH3?
Due to the presence of OH-, the results when a few drops of NH3 (aq) is added are the same as when a few drops of NaOH is added
- all form Metal hydroxide precipitates
What is the observation of each of the metal ion solutions with A few drops of NH3 and EXCESS NH3 (aq)?
- CuSO4 - few drops = forms a blue precipitate.
Excess = forms a deep blue solution, so dissolves in excess NaOH - FeSO4 - Few drops = forms a green precipitate.
Excess = green precipitate formed - does not dissolve in water - Fe(SO3)4 - Few drops = forms a brown precipitate.
Excess = brown precipitate - does not dissolve in excess Ammonia - Al2(SO4)3 - Few drops = white precipitate formed
Excess = White precipitate - does not dissolve in excess NH3
M2+ metal ions in dilute ammonium solution form..?
[M(OH)2(H2O)4] (s) (+ 2H2O) - same as NaOH
M3+ metal ions in dilute Ammonium solution form?
[M(OH)3(H2O)3] (s) ~(+ 3H2O) - same as NaOH
Write equations to the reactions of the following Metal ion solutions with A few drops of Ammonia (dilute ammonia):
1. FeSO4
2. Fe2(SO4)3
3. Al2(SO4)3
- [Fe(H2O)6]2+ (aq) + 2NH3 (aq) —-> [Fe(OH)2(H2O)4] (S) + 2NH4+ (aq)
- [Fe(H2O)6]3+ (aq) + 3NH3 (aq) —–> [Fe(OH)3(H2O)3] (s) + 3NH4+ (aq)
3.[Al(H2O)6]3+ (aq) + 3NH3 (aq) —-> [Al(OH)3(H2O)3] (s) + 3NH3 (aq)
(All of these reaction do not dissolve in excess NH3)
Which of the following reactions above oxidises to form a different colour precipitate? Write an equation to show this?
Reaction 1 - The green precipitate can oxidise to a brown precipitate
4[Fe(OH)2(H2O)4] (s) + O2 (g) —> 4[Fe(OH)3(H2O)3] (s) + 2H2O (l)
Why doesn’t NH3 cause further Hydrolysis when added in excess?
- As NH3 is only a weak base it does not cause further hydrolysis when added in excess
- Instead Ammine complexes are formed, with NH3 ligands being substituted for water molecules in the complex ion.
Which of the metal ion solutions forms a ammine complex ion in ammonia solution?
Cu2+ - CuSO4
Via what type of reaction, does Cu2+ form Ammine complex ions?
Via partial Ligand substitution
Write out equations to show the reaction of Copper (II) sulphate with Few drops of Ammonia, what acts as a Bronstead Lowry base and what acts as a Bronstead Lowry acid
- [Cu(H2O)6]2+ (aq) + 2NH3 (aq) ⇌ [Cu(H2O)4 (OH)2] (s) + 2NH4+ (aq)
- [Cu(H2O)6]2+ acts as a Bronstead Lowry acid
- 2NH3 acts as a Bronstead Lowry base
Write out equations to show the reaction of Copper (II) sulphate with Excess Ammonia, what acts as a Lewis base and what acts as a Lewis acid
- [Cu(H2O)4(OH)2] (s) + 4NH3 (aq) —> [Cu(H2O)2(NH3)4]2+ (aq) + 2H2O (l) + 2OH- (aq)
- [Cu(H2O)4(OH)2] (s) acts as a lewis acid by accepting a pair of electrons
- 4NH3 acts as a lewis base
Why is this reaction considered Partial Ligand substitution?
Partial ligand substitution as only 4 out of 6 water molecules are replaced by NH3
What is the overall equation for the reaction of CuSO4 (copper (II) sulphate) with Ammonia solution?
[Cu(H2O)6]2+ (aq) + 4NH3 (aq) ⇌ [Cu(H2O)2(NH3)4]2+ (aq) + 4H2O (l)
Complete some exam questions
Reactions of Hexa Aqua Metal ions with Sodium carbonate Na2CO3 and Concentrated HCl
What do Metal 2+ ions form with Sodium Carbonate (Na2CO3) solution?
- Form metal (11) carbonate precipitates
- [M(H2O)6]2+ (aq) + CO32- –> MCO3 (s) + 6H2O (l)
What do Metal 3+ ions form with Na2CO3 solution?
- Form metal (III) hydroxides precipitates
- 2[m(H2O)6]3+ + 3CO32- –> 2[M(H2O)3(OH)3] (s) + 3CO2 (g) + 3H2O (l)
- fizzes - bubbles of CO2 gas formed
State the observation when Na2CO3 is added to the following metal compounds:
1. CuSO4 (aq)
2. FeCl2 (aq)
3. Fe2(SO4)3 (aq)
4. Al(NO3)3 (aq)
- Blue solution to Blue-green precipitate
- pale green colour to green precipitate
- Yellow/ purple solution to a brown precipitate + CO2 gas
- colourless solution to a white precipitate + CO2 gas
Write equations to show the reactions of Na2CO3 with the following hexa aqua metal ions:
1. Cu2+
2. Fe 2+
3. Fe3+
4. Al3+
- [Cu(H2O)6]2+ (aq) + CO3^2- –> CuCO3 (s) + 6H2O (l)
- [Fe(H2O)6]2+ (aq) + CO32- –> FeCO3 (s) + 6H2O (l)
- 2[Fe(H2O)6]3+ + 3CO32- –> 2[Fe(H2O)3(OH)3] (s) + 3CO2 (g) + 3H2O (l)
- 2[Al(H2O)6]3+ + 3CO32- –> 2[Al(H2O)3(OH)3] (s) + 3CO2 (g) + 3H2O (l)
Why does the reaction with Na2CO3 not produce any fizzing/ bubbles with Metal 2+ ions but does produce with Metal 3+ ions?
- there is no fizzing with metal 2+ ions because [M(H2O)6]2+ is not acidic enough, Ph = 6, very weakly acidic
- Whereas, there is fizzing/ bubbles of CO2 with 2[M(H2O)6]3+ as it it more acidic, pH =3.
Reactions with Concentrated HCl
What do Hexa aqua metal ions form with concentrated HCl?
they form tetrahedral Chlorocomplexes
Why can only 4 fit around?
Cl - is larger than H2O and OH-, so only 4 can fit around the metal ion
State the observations of the following ions with Concentrated HCl:
1. Cu2+
2. Fe2+
3. Fe3+
4. Al3+
- blue solution turns to a yellow-green solution
- pale green solution turns to a green solution
- purple solution turns to a yellow solution
- colourless solution forms a colourless solution
Write equations for the reaction of the following metal ions with Na2CO3:
1. Cu2+
2. Fe2+
3. Fe3+
4. Al3+
- Cu2+ (aq) + 4CL- (aq) —> [CuCL4]2- (aq)
- Fe2+ (aq) + 4CL- (aq) —> [FeCL4]2- (aq)
- Fe3+ (aq) + 4CL- (aq) —> [FeCL4]- (aq)
- Al3+ (aq) + 4CL- (aq) —> [AlCL4]- (aq)
Hydrolysis Reactions
what is a hydrolysis reaction?
when water is added to hexa aqua metal ion it is called a hydrolysis reaction as it is a reaction with water where the O-H bonds in water are broken
Draw an equation to show the hydrolysis of hexa aqua metal ions (2+). Describe what acts as a Bronstead-Lowry acid and base.
[M(H2O)6]2+ (aq) + H2O (l) ⇌ [M(H2O)5(OH)]+ (aq) + H3O+ (aq)
- [M(H2O)6]2+ (aq) = B-L acid = proton donor
- H2O (l) = B-L Base = proton acceptor
what type of acids are hex aqua metal ions?
hexa aqua [M(H2O)6]n+ are all Bronstead Lowry acids, as they are all proton donors and the water is a bronstead lowry base
What is the pH of hexa aqua ions?
- M2+ = pH = 6/5 - weak acids - not very acidic
- M3+ pH = 3, are weak acids
What does the acidity of the hexa aqua metal ion depend on?
- charge/ size ratio
- the position of equilibrium in the hydrolysis reaction
describe the charge to size ration of hexa aqua metal ions?
- M2+ = ions are small with a large charge, so they have a high charge/size ratio
- M3+ = have a smaller charge, hence a smaller charge/ size ratio
Because of the charge/size ratio, M3+ ions are more…?
so M3+ ions are more polarising than M2+, and polarise the O-H bond in water to a greater extent, so H+ can be lost more easily, so Greater [H+], and lower pH
describe the effect of acidity of M2+ the position of equilibrium?
- [M(H2O)6]2+ (aq) + H2O (l) ⇌ [M(H2O)5(OH)]+ (aq) + H3O+ (aq)
- only one molecule in 100,00 dissociates/hydrolyses so equilibrium way over to left, so very weakly acidic, pH = 6/6.5
describe the effect of M3+ acidity on the position of equilibrium?
- [M(H2O)6]3+ (aq) + H2O (l) ⇌ [M(H2O)5(OH)]2+ (aq) + H3O+ (aq)
- one molcule in 1000 dissociates/hydrolyses, so equilibrium over to the left, so weakly acidic, pH=3
Describe the effect of M4+ acidity of the position of equilibrium?
- [M(H2O)6]4+ (aq) + 4H2O (l) ⇌ [M(H2O)2(OH)4] (s) + 4H3O+ (aq)
- undergoes complete hydrolysis to form metal (IV) hydroxide precipitates. Strongly acidic solution pH = 0
What is a ligand?
a ligand is a molecule or ion which donates a pair of electrons to a metal ion to form a coordinate bond
what is a ligand substitution reaction?
- ligands can swap places with other ligands in ligand substitution reactions
- usually involves a change in colour
- ligand substitution reactions are lewis acid - lewis base reactions
- can have partial or complete substitution
what is complete ligand substitution?
give an example.
complete ligand substitution involves the total replacement of all the ligands by another ligand.
e.g ([Co(H2O)6]2+ (aq) + 6NH3 (aq) ⇌ [Co(NH3)6]2+ (aq) + 6H2O+ (l)
pink solution turns to a pale brown solution
coordination number = remains the same
why will ligand substitution with NH3 and H2O be more likely to occur/ occur without a change in co-ordination number?
H2O and NH3 are similar in size and charge, so ligand substitution by NH3 of H2O ligands and vice versa, occur without a change in co-ordination number
When is there a change in coordination number?
Cl- ions are larger than H2O, so not as many can fit around the central metal ion, so there is a change in co-ordination number
[Cu(H2O)6]2+ (aq) reacts with HCl to form a complex with less ligands, what is this complex. describe what occurs during this reaction and write an equation to show this reaction?
- [Cu(H2O)6]2+ (aq) + 4Cl- (aq) ⇌ [CuCl4]2- (aq) + 6H20+ (l)
- changes from an octahedral complex to a tetrahedral complex
- changes from a blue solution to a yellow-green solution
- coordination number changes from 6 to 4
what is incomplete ligand substitution?
Give an example.
incomplete involves only some of the ligands being replaced by another ligand
e.g [Cu(H2O)6]2+ (aq) + 4NH3 (l) ⇌ [Cu(NH3)4(H2O)32]+ (aq) + 4H2O+ (aq)
(blue solution turns deep blue solution)
What are chelates?
chelates are complexes of metals with bidentate or multidentate ligands
what are unidentate ligands?
unidentate ligands have one pair of electrons to donate to form one coordinate bond
what are Bidentate ligands?
have two lone pairs of electrons to donate and form two coordinate bonds
what are multidentate ligands?
have more than two lone pairs of electrons to donate and form more than two coordinate bonds
Give examples of some chelates?
EDTA4-, C2O42-, Diamine
Why are chelates more stable than complexes of unidentate ligand?
- more moles of product
- increase in entropy, increase in disorder
- ΔG more negative, free energy change more negative
Amphoteric substances
What are amphoteric substances?
Amphoteric substances dissolve in both acids and alkali’s
What are two examples of amphoteric substances?
- Al2O3 (s) aluminium oxide
- [Al(OH)3(H2O)3] (s) - aluminium hydroxide
State observation when Aluminium oxide dissolves in both an acid and an alkali?
white solid forms a colourless solution
Write equations showing that aluminium oxide (Al2O3) is amphoteric?
In acid:
- Al2O3 (s) + 6H+ (aq) + 9H2O (l) —-> 2[Al(H2O)6]3+ (aq)
In alkali:
- Al2O3 (s) + 2OH- (aq) + 3h2O —-> 2[Al(OH)4]- (aq)
State the observation when aluminium hydroxide dissolves in both an acid and alkali?
white precipitate turns into a colourless solution
write equations showing that aluminium hydroxide is amphoteric.
in acid:
- [Al(OH)3(H2O)3] (s) + 3H+ (aq) —-> [Al(H2O)6]3+ (aq)
In Alkali:
- [Al(OH)3(H2O)3] (s) + OH+ (aq) —-> [Al(OH)4]- (aq) + 3H2O (l)
Vanadium
What colour is Ammonium Vandanate 5 (V) at room temperature?
Orange solid
An orange solid of Ammonium Vanadate 5 dissolves in water to form what colour solution?
What ions are present in this solution?
Orange solution - containing VO3-, vanadate (V) ion.
What happens when an acid is added to the solution?
Draw an equation to show.
- When an acid is added an acid-base reaction occurs forming a yellow solution containing
- VO3- + 2H+ ——> VO2+ + H2O
Why is this reaction not a redox reaction?
There is no change in oxidation state
With what metal can vanadium be reduced?
- By the addition of Zinc metal
- Vanadium can be reduced to Vanadium 4 (IV), Vanadium 3 (III) and Vanadium 2(II)
With what acid can Vanadium be Oxidised by?
- By the addition of Acidified Potassium Permangante
- Vanadium (II) can be to Vanadium (III), Vanadium (IV) and Vanadium 5 (V)
How can you tell is a change in oxidation state has occurred in the reduction/Oxidation of Vanadium?
- If there is a colour change
Describe How redox reaction of Vanadium is carried out?
- Pour 5cm3 of acidified ammonium vanadate solution in a test tube
- Record all the colour changes when a little powdered zinc metal (1/4 spatula) is added to the ammonium vanadate (V) solution and place cotton wool over the top of the test tube.
- After the first minute has passes (DO NOT SWIRL FOR THE FIRST MINUTE) swirl gently.
- Record all the colour changes that occur over 2-10 minutes.
- Filter the solution using filter paper + funnel formed after 10 minutes into a test tube and keep the filtrate solution.
- Put 1cm depth of this filtrate into another and add Acidified potassium manganate solution dropwise to the filtrate solution. Record all the colour changes.
What were the results of the reaction?
The colour of the solution, changes from
yellow to
Blue to
Green to
Purple to
Why did we see a green solution appear before we saw a blue solution?
Because the yellow solution of VO2^+ (aq) and blue solution of VO^2+ (aq) will mix and cause a green looking solution.
Why is the cotton wool needed at the top of the test tube in order to form a purple solution?
To prevent oxygen from the air oxidising the purple V 2+ solution into the green V 3+ solution
Why will the purple solution go green when left to stand in air?
The purple V2+ gets oxidised by O2 in air to V3+
REMEMBER: IN THIS REACTION, ZINC IS THE R…?
REDUCING AGENT.
VO2+ is reduced to VO2+, in what conditions?
Draw a redox equation to show this reaction?
- Acidic conditions
- VO2+ + 2H+ +e- —–> VO2+ + H2O
Draw the Redox equation for Zinc?
Draw the overall redox equation?
- Zn —-> Zn2+ + 2e-
Overall: - 2VO2+ + Zn +4H+ —> 2VO2+ + Zn2+ + 2H2O
DONE!!
