Reaction of transition metals

Question 1

what happens to the colours during the addition of zinc to vanadium (v) in acidic solution

Answer 1

reduce the vanadium down through each successive oxidation state
The colour would successively change from yellow to blue to green to violet

Question 2

how do we add the half equations from redox equation and e value table

Answer 2

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

Question 3

how can chromate be converted to dichoromate

Answer 3

2CrO42- (aq) + 2H+ (aq) ⇌ Cr2O72- (aq) + H2O (l)

Question 4

explain addition of acid or alkali to
2CrO42- (aq) + 2H+ (aq) ⇌ Cr2O72- (aq) + H2O (l)

Answer 4

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

Question 5

is 2CrO42- (aq) + 2H+ (aq) ⇌ Cr2O72- (aq) + H2O (l) a redox reaction

Answer 5

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

Question 6

how do metal ions react with excess ammonia

Answer 6

through ligand substitution

Question 7

how can you remember number of hydroxides in the precipitate

Answer 7

charge of the metal aqua ion

Question 8

[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

Answer 8

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]

Question 9

reaction of transition metal ion with sodium hydroxide

Answer 9

[Cr(H2O)6]3+ (aq) + 3OH- (aq) → [Cr(H2O)3(OH)3] (s) +3H2O (l)

Question 10

reaction of transition metal ion with excess sodium hydroxide

Answer 10

[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)

Question 11

can chromium(III) hydroxide also act as a base

Answer 11

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)

Question 12

what is a metal hydroxide called that can act as an acid and a base

Answer 12

amphoteric hydroxide

Question 13

what type of reaction occurs when excess NH3 is reacted with Cu, Co and Cr

Answer 13

With excess NH3 ligand substitution reactions occur with Cu, Co and Cr and their precipitates dissolve

Question 14

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

Answer 14

[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

Question 15

reaction of copper (II) hydroxide precipitate with concentrated/ excess HCL

colour

Answer 15

[Cu(H2O)6]2+ (aq) + 4Cl– (aq) → [CuCl4]2– (aq) + 6H2O (l)

forms a yellow solution

Question 16

reaction of cobalt metal aqua ion with concentrated/ excess HCL

colour

Answer 16

Pink [Co(H2O)6]2+ (aq) forming blue [CoCl4]2– (aq)

Question 17

reaction of iron hydroxide precipitate with concentrated/ excess HCL

colour

Answer 17

Yellow [Fe(H2O)6]3+ (aq) forming orange [FeCl4]– (aq)

Question 18

what is the purpose of ligand exchange

Answer 18

forms a new complex that is more stable than the original one

Question 19

when are there no changes in coordination number or geometry of the complex and when are there changes

Answer 19

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

Question 20

what does an addition of high concentration of chloride ions to aqueous ions lead to

use Copper (II) sulfate as an example

Answer 20

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)

Question 21

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)

Answer 21

all six water ligands have been replaced by four chloride ions

Question 22

why is the green colour seen

Answer 22

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

Question 23

reaction of hexaaquacobalt(II) with HCL

Answer 23

[Co(H2O)6]2+ (aq) + 4Cl- (aq) ⇌ [CoCl4]2- (aq) + 6H2O (l)

Question 24

what is the chelate effect and would ΔGꝋ be negative/positive

Answer 24

The replacement of monodentate ligands with bidentate and multidentate ligands in complex

It is an energetically favourable reaction, meaning that ΔGꝋ is negative

Question 25

explain the shape of cobalt II aqua ion using electron pair repulsion

Answer 25

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

Question 26

discuss why scandium and zinc are d block elements but not transition metals

Answer 26

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)

Question 27

why are zinc ions colourless

Answer 27

(zinc (ions) / Zn2+) has / have a full
(3)d sub-shell

electrons cannot be promoted / excited to higher (3)d orbitals

Question 28

why cant ammonia act as a ligand

Answer 28

ammonium ions do not have a lone pair (of electrons for bonding)

Question 29

Explain why the complex ions [Co(NHs)62+ and [Co(H20)6]?+ are coloured and have different colours.

Answer 29

*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

Question 30

why can inhaling carbon monoxide fatal

Answer 30

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

Question 31

Explain how impurities in the gaseous reactants could make the catalyst less effective

Answer 31

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)