Hydroxide Reactions And Vanadium

Question 1

How does colour of vanadium change as it is reduced

Answer 1

5+ yellow
4 blue
3 green
2 violet

Question 2

How can vanadium be reduced

Answer 2

Zinc in acidic conditions

Question 3

What conditions are required for transition metal ions to be reduced

Answer 3

Acidic conditions

Question 4

What conditions are required for transition metal ions to be oxidised

Answer 4

React with water to produce OH- ions and therefore alkaline conditions required

Question 5

What are the most stable oxidation states of chromium

Answer 5

+6, +3 and +2

Question 6

How can Cr2O7 2- be reduced and to what

Answer 6

To Cr3+/2+ by reduction with zinc in acidic conditions

Question 7

How is Cr3+ oxidised and to what

Answer 7

By hydrogen peroxide in alkaline conditions, reaction first forms CrO4 2- which is then converted to Cr2O7 2- by acidification

Question 8

Equilibrium between CrO4 2- and Cr2O7 2- and how does acidification affect this

Answer 8

2CrO4 2- + 2H+ double arrow Cr2O7 2- + H2O
-acidification of solution containing CrO4 2- will cause equilibrium to shift to the right to use up the additional H+ ions so concen of Cr2O7 2- will increase

Question 9

If hydroxide precipitate dissolves in excess hydroxide what type of reaction is this

Answer 9

Acid base reaction as involves deprotonation of ligands for 3+ ions except iron

Question 10

What does amphoteric mean

Answer 10

Species that reacts and dissolves in both acids and bases (so able to act as both an acid and base)

Question 11

If ammonia ligand complex precip dissolves in excess ammonia what type of reaction is this

Answer 11

Ligand substitution except +2/+3 iron which do not react

Question 12

Two equations for hydrolysis of M2+ ions

Answer 12

[M(H2O)6] 2+ + H2O double arrow [M(H2O)5OH]+ + H3O+
[M(H2O)5OH]+ + H2O double arrow [M(H2O)4(OH)2] (s) + H3O+

Question 13

Which species form precipitates

Answer 13

Neutral ones

Question 14

What is a Lewis base

Answer 14

Donates a pair of electrons

Question 15

Actual and seen colour and formula of metal-aqua ion for Cr3+

Answer 15

[Cr(H2O)6] 3+ and is violet but appears green due to hydrolysis in water

Question 16

Series of reactions between chromium 3+ metal-aqua ion and OH-/ excess

Answer 16

With OH-:
Cr(OH)3 (H2O)3 (green precip)
Excess OH-:
[Cr(OH)6]3- (green solution)

Question 17

Colour and formula of metal-aqua ion for Fe2+

Answer 17

[Fe(H2O)6]2+ , green solution

Question 18

Series of reaction of Fe2+ metal aqua ion with OH-/ excess

Answer 18

With OH-:
Fe(OH)2(H2O)4 green precip
-with excess OH- no change so insoluble in excess

Question 19

Colour and formula of metal-aqua ion for Fe3+

Answer 19

[Fe(H2O)6]3+ yellow solution

Question 20

Series of reactions of Fe3+ metal aqua ion with OH-/ excess

Answer 20

With OH-:
Fe(H2O)3(OH)3 brown precip
-no change with excess

Question 21

Colour and formula of metal-aqua ion for Co2+

Answer 21

[Co(H2O)6] 2+ pink solution

Question 22

Series of reactions of Co2+ metal aqua ion with OH-/excess

Answer 22

With OH-:
Co(OH)2(H2O)4 blue precip
-no change with excess

Question 23

Colour and formula of metal-aqua ion for Cu2+

Answer 23

[Cu(H2O)6] 2+ blue solution

Question 24

Series of reactions between Cu2+ and OH-/ excess

Answer 24

With OH-:
Cu(OH)2(H2O)4 blue precip
-no change with excess

Question 25

What is the number of OH- substituted the same as for just OH- not with excess

Answer 25

The same as the value of the charge on the initial ion

Question 26

How does Fe2+ hydroxide precip change upon standing

Answer 26

Changes from green to rusty brown due to oxidisation by air to form Fe(OH)3(H2O)3 (s)

Question 27

Colour of CrO4 2- chromate (VI)

Answer 27

Yellow

Question 28

Colour of Cr2O7 2- (dichromate)

Answer 28

Orange

Question 29

How does adding hydroxide ions shift equilibrium of CrO4 2- reacting to form Cr2O7 2-

Answer 29

Shifts equilibrium to the left as more OH- to react with H+ so will form water which is on right hand side of equation meaning will shift away from water to use it up so more CrO4 2- produced

Question 30

Example of oxidising agent

Answer 30

Hydrogen peroxide

Question 31

Why are compounds in alkaline easier to oxidise

Answer 31

As in alkaline the OH- will deprotonate the water ligands producing negatively charged complex and it is easier to remove an electron from a negatively charged ion as the negative charge of the OH- ligands stabilises the greater positive charge of the oxidation state

Question 32

What happens when excess NaOH added to [Cr(H2O)6] 3+ (aq)

Answer 32

Will form [Cr(OH)6] 3- (aq) which is easier to oxidise and is green solution

Question 33

How to balance half equations in alkaline conditions

Answer 33

Add H2O to balance oxygen and H+ to balance hydrogen, add enough OH- to the side with hydrogen on it to cancel them out and form water and add the same OH- to the other side

Question 34

Why type of reaction is the chromate (VI) - dichromate (VI) equilibrium

Answer 34

Acid base reaction