Reaction of transition metals Flashcards
what happens to the colours during the addition of zinc to vanadium (v) in acidic solution
reduce the vanadium down through each successive oxidation state
The colour would successively change from yellow to blue to green to violet
how do we add the half equations from redox equation and e value table
find the two half equations you want depending on what type of reduction you are looking for
whichever equation has a more negative E value will be reversed then added to the other equation
how can chromate be converted to dichoromate
2CrO42- (aq) + 2H+ (aq) ⇌ Cr2O72- (aq) + H2O (l)
explain addition of acid or alkali to
2CrO42- (aq) + 2H+ (aq) ⇌ Cr2O72- (aq) + H2O (l)
Chromate(VI) ions are stable in alkaline solution, but in acidic conditions the dichromate(VI) ion is more stable
Addition of acid will push the equilibrium to the dichromate
This results in a colour change from yellow to orange
Addition of alkali will remove the H+ ions and push the equilibrium to the chromate
is 2CrO42- (aq) + 2H+ (aq) ⇌ Cr2O72- (aq) + H2O (l) a redox reaction
This is not a redox reaction as both the chromate and dichromate ions have an oxidation number of +6
This is an acid base reaction
how do metal ions react with excess ammonia
through ligand substitution
how can you remember number of hydroxides in the precipitate
charge of the metal aqua ion
[Cu(H2O)6]2+ (aq) + 2OH- (aq) → [Cu(H2O)4(OH)2] (s) + 2H2O (l)
explain how this is a deprotonation reaction and not a ligand substitution reaction
This seems like a ligand substitution reaction - two hydroxide ions replacing two water molecules
However this is actually a deprotonation reaction - two hydroxide ions removing hydrogen ions from two of the water ligands converting them into water molecules
The two ligands that have lost hydrogen ions are now hydroxide ligands
Cu(H2O)6]2+
Cu(H2O)4(OH)2]
reaction of transition metal ion with sodium hydroxide
[Cr(H2O)6]3+ (aq) + 3OH- (aq) → [Cr(H2O)3(OH)3] (s) +3H2O (l)
reaction of transition metal ion with excess sodium hydroxide
[Cr(H2O)6]3+ (aq) + 3OH- (aq) → [Cr(H2O)3(OH)3] (s) +3H2O (l)
[Cr(H2O)3(OH)3] (s) + 3OH- (aq) → [Cr(OH)6]3- (aq) + 3H2O (l)
can chromium(III) hydroxide also act as a base
Chromium(III) hydroxide can also act as a base because it can react with acids as follows
[Cr(H2O)3(OH)3] (s) + 3H+ (aq) → [Cr(H2O)6]3+ (aq)
what is a metal hydroxide called that can act as an acid and a base
amphoteric hydroxide
what type of reaction occurs when excess NH3 is reacted with Cu, Co and Cr
With excess NH3 ligand substitution reactions occur with Cu, Co and Cr and their precipitates dissolve
write equation for when excess ammonia is added to copper (II) hydroxide precipitate
explain how it is ligand substitution and how NH3 is acting as a lewis base
[Cu(H2O)4(OH)2] (s) + 4NH3 (aq) → [Cu(NH3)4(H2O)2]2+ (aq) + 2H2O (l) + 2OH- (aq)
This is a ligand substitution - four ammonia molecules replace two water molecules and two hydroxide ions
In these reactions, NH3 is acting as a Lewis base donating an electron pair
reaction of copper (II) hydroxide precipitate with concentrated/ excess HCL
colour
[Cu(H2O)6]2+ (aq) + 4Cl– (aq) → [CuCl4]2– (aq) + 6H2O (l)
forms a yellow solution
reaction of cobalt metal aqua ion with concentrated/ excess HCL
colour
Pink [Co(H2O)6]2+ (aq) forming blue [CoCl4]2– (aq)
reaction of iron hydroxide precipitate with concentrated/ excess HCL
colour
Yellow [Fe(H2O)6]3+ (aq) forming orange [FeCl4]– (aq)
what is the purpose of ligand exchange
forms a new complex that is more stable than the original one
when are there no changes in coordination number or geometry of the complex and when are there changes
if the ligands are of a similar size
But, if the ligands are of a different size, for example water ligands and chloride ligands, then a change in coordination number and the geometry of the complex will occur
what does an addition of high concentration of chloride ions to aqueous ions lead to
use Copper (II) sulfate as an example
a ligand substitution reaction.
The Cl- ligand is larger than the uncharged H2O and NH3 ligands so therefore ligand exchange can involve a change of co-ordination number
colour changes from blue to green then finally yellow
[Cu(H2O)6]2+ (aq) + 4Cl- (aq) ⇌ [CuCl4]2- (aq) + 6H2O (l)
how is there a change in coordination number from 6 to 4 in this reaction [Cu(H2O)6]2+ (aq) + 4Cl- (aq) ⇌ [CuCl4]2- (aq) + 6H2O (l)
all six water ligands have been replaced by four chloride ions
why is the green colour seen
The hexaaquacopper(II) ion is blue
The tetrachlorocuprate(II) ion is yellow
The green colour is due to a mixture of the blue and yellow complex ions
reaction of hexaaquacobalt(II) with HCL
[Co(H2O)6]2+ (aq) + 4Cl- (aq) ⇌ [CoCl4]2- (aq) + 6H2O (l)
what is the chelate effect and would ΔGꝋ be negative/positive
The replacement of monodentate ligands with bidentate and multidentate ligands in complex
It is an energetically favourable reaction, meaning that ΔGꝋ is negative
explain the shape of cobalt II aqua ion using electron pair repulsion
Electron pairs
* 6 (dative) pairs of (bonding) electrons (around cobalt ion) (1)
Minimise repulsion
* (electron / bond pairs) arranged in order to minimise repulsion
(1)
Shape
so shape is octahedral
discuss why scandium and zinc are d block elements but not transition metals
both elements / atoms have the last added electron in the
d-subshell / d orbital (so are d-block elements)
(1)
but neither forms a (stable) ion with an incomplete d-subshell / d orbital (so are not transition metals)
(1)
* Zn?* is 1s+2s22p63s23p63diO (so d subshell is full)
(1)
* Sc is 1s+2s 2p$3s3p° (so d subshell is empty)
why are zinc ions colourless
(zinc (ions) / Zn2+) has / have a full
(3)d sub-shell
electrons cannot be promoted / excited to higher (3)d orbitals
why cant ammonia act as a ligand
ammonium ions do not have a lone pair (of electrons for bonding)
Explain why the complex ions [Co(NHs)62+ and [Co(H20)6]?+ are coloured and have different colours.
*d orbitals/d sub-shell split (into two different energies)
(1)
- difference in energy depends on the ligands
(1)
difference in energy leads in different frequencies/wavelengths/photons of light absorbed
(1)
(so) the unabsorbed
frequencies/wavelengths/photons are reflected/transmitted
why can inhaling carbon monoxide fatal
carbon monoxide replaces / takes the place of the oxygen molecule
(and may be toxic because) it binds strongly to the Fe?+ (ion)
prevents oxygen being carried to the cells / organs / around the body / blood
Explain how impurities in the gaseous reactants could make the catalyst less effective
impurities adsorb onto (catalyst)
surface or impurities occupv active sites or
impurities bond / bind to (catalyst) surface
(1)
M2
impurities prevent bond weakening in the reactants or
less surface area (of catalyst) / fewer active sites available for reaction
(1)
M3
impurities form strong bonds (to surface) or
impurities less likely to desorb (from surface)
