Reactions of Ions in Aqueous Solutions

Question 1

what is a metal aqua complex

Answer 1

it is a complex that is formed when a transition metal compound is added to water

Question 2

what affects how acidic a metal aqua complex is and why are they acidic

Answer 2

the charge of the complex affects how how acidic the metal complex is. metal aqua ions are acidic when in solution

Question 3

what is the reaction when [Fe(H2O)6]2+ reacts with water and what is this reaction called

Answer 3

[Fe(H2O)6]^2+ + H2O = [Fe(H2O)5(OH)]^+ + H3O+

the hydroxonium ion is what makes the solution acidic.

this is a hydrolysis reaction

Question 4

what happens when you react [Fe(H2O)6]^3+ and water and what is this reaction called

Answer 4

[Fe(H2O)6]^3+ + H2O = [Fe(H2O)5(OH)]^2+ + H3O+

this is also a hydrolysis reaction

Question 5

what is the difference between the hydrolysis of a 2+ complex and a 3+ complex

Answer 5

• 2+ complex ions dissociate weakly so they are not very acidic
• 3+ complex ions dissociate more readily than 2+ complexes and are more acidic.

Question 6

why are 3+ complexes more acidic than 2+ complexes and why does this allow the complex to dissociate to form a more acidic solution

Answer 6

this is because 3+ metal ions have a higher charge density than 2+ metal ions. this is because they have a larger charge and are small.

• this means that the 3+ metal ions are more polarising than the 2+ metal ions. this means that they attract the O-H bond in the ligands more strongly, this weakens the bond. this means that the H+ ion is more likely to be lost which means the 3+ metal ions form a more acidic solution.

Question 7

what is the further hydrolysis of metal aqua ions

Answer 7

it is the addition of more water to the metal aqua ion to more an insoluble metal hydroxide.
e.g. metal(H2O)3(OH)3 (s)
the complex no longer has a charge.

Question 8

why is an insoluble metal hydroxide formed when the metal aqua ion is further hydrolysised

Answer 8

this is because a neutral complex is formed which is solid which forms a precipitate in solution.

Question 9

what are the two general reactions for when a 2+ & 3+ metal aqua ions are further hydrolsised to form an insoluble metal hydroxide

Answer 9

[M(H2O)6]^2+ + 2H2O = M(H2O)4(OH)2 + 2H3O^+

[M(H2O)6]^3+ + 3H2O = M(H2O)3(OH)3 + 3H3O^+

Question 10

how can you reverse the formation of the metal hydroxide formed from hydrolysis

Answer 10

add and acid (h+) and the precipitate will dissolve. this is only possible when the metal hydroxide is amphoteric e.g aluminium

Question 11

what happens when you add a base (OH-) or and acid (H3O+) to aluminium hydroxide

Answer 11

Al(H2O)3(OH)3 + OH^- = [Al(H2O)2(OH)4]^- + H2O

Al(H2O)3(OH)3 + 3H3O^+ = [Al(H2O)6]^3+ + 3H2O

Question 12

what does adding ammonia to a metal aqua ion do and what could happen when you add an excess of ammonia

Answer 12

adding ammonia to metal aqua ions form a metal hydroxide precipitate too.

sometimes when adding an excess of ammonia could lead to partial ligand subsitution.

Question 13

what is the equilibrium equation for when ammoina is in solution

Answer 13

NH3 + H2O ⇌ NH4^+ + OH^-

Question 14

what is the reaction for when and excess of ammonia to cu(H2O)4(OH)2

Answer 14

the ligands are displaced an a charge soluble complex is formed
Cu(H2O)4(OH)2 + 4NH3 = [Cu(NH3)4(H2O)2]^2+ + 2OH^- + 2H2O

Question 15

what happens when you add sodium carbonate to 2+ metal aqua ions

Answer 15

it forms metal carbonate precipitates

Question 16

what is the general formula for when you react a 2+ metal aqua ion with carbonate ions

Answer 16

[M(H2O)6]^2+ + CO3^2- ⇌ MCO3 + 6H2O

Question 17

what is the general formula for when you react a 3+ metal aqua ion with carbonate ions and why does this occur

Answer 17

2[M(H2O)6]^3+ + 3CO3^2- ⇌ 2M(H2O)3(OH)3 + 3CO2 + 3H2O

• this is because 3+ metal ions are more acidic than 2+ and therfore ther is more H3O^+ ions in solution so the carbonate reacts with the H3O+ instead of displacing the water ligands.

Question 18

what are the steps of test tube reactions that are used to identify an unknown metal ion solution

Answer 18

1. add sample of unknown metal ion solution into 3 test tubes
2. add sodium hydroxide drop by drop to test tube 1 and observe any changes. and then add more sodium hydroxide to see if an excess results in any further change
3. add ammonia solution to test tube 2 drop by drop and observe any change. then add in excess to see if it results in a change
   4.then add sodium carbonate drop by drop and record any change

Question 19

what is a safety precaution that can be used when dealing with ammonia

Answer 19

ammonia gives off pungent fumes and should therefore be done in a fume cupboard

Question 20

what happens when you add an excess of sodium hydroxide to aluminium hydroxide

Answer 20

the precipitate dissolves when in excess and this is because aluminium is amphoteric

Question 21

what is the colour for :
[Cu(H2O)6]^2+
[Fe(H2O)6]^2+
[Fe(H2O)6]^3+
[Al(H2O)6]^3+

Answer 21

[Cu(H2O)6]^2+ = blue sol
[Fe(H2O)6]^2+ = green sol
[Fe(H2O)6]^3+ = yellow sol
[Al(H2O)6]^3+ = colourless sol

Question 22

what is the colour change for adding HCL to :
[Cu(H2O)6]^2+
[Fe(H2O)6]^2+
[Fe(H2O)6]^3+
[Al(H2O)6]^3+

Answer 22

[Cu(H2O)6]^2+ = gr -yel sol
[Fe(H2O)6]^2+ = bl - yel sol
[Fe(H2O)6]^3+ = or - yel sol
[Al(H2O)6]^3+ = remains colourless

Question 23

what is the colour change when ammonia (NH3) is added to:
[Cu(H2O)6]^2+
[Fe(H2O)6]^2+
[Fe(H2O)6]^3+
[Al(H2O)6]^3+

Answer 23

[Cu(H2O)6]^2+ = blue sol - pale blue precipitate ( in ex deep blue solution)
[Fe(H2O)6]^2+ = green sol - green precipitate
[Fe(H2O)6]^3+ = orange sol - brown precipitate
[Al(H2O)6]^3+ = colorless sol - white precipitate

Question 24

what is the colour change when you add some OH- to:
[Cu(H2O)6]^2+
[Fe(H2O)6]^2+
[Fe(H2O)6]^3+
[Al(H2O)6]^3+

Answer 24

[Cu(H2O)6]^2+ = blue sol -
pale blue precipitate
[Fe(H2O)6]^2+ = green sol - green precipitate
[Fe(H2O)6]^3+ = orange sol - orange precipitate
[Al(H2O)6]^3+ = colorless sol - white precipitate

Question 25

what is the colour change when you add OH- in excess to:
[Cu(H2O)6]^2+
[Fe(H2O)6]^2+
[Fe(H2O)6]^3+
[Al(H2O)6]^3+

Answer 25

[Cu(H2O)6]^2+ = no change
[Fe(H2O)6]^2+ = no change
[Fe(H2O)6]^3+ = no change
[Al(H2O)6]^3+ = colorless solution

Question 26

what is the colour change when you add Na2CO3 in excess to:
[Cu(H2O)6]^2+
[Fe(H2O)6]^2+
[Fe(H2O)6]^3+
[Al(H2O)6]^3+

Answer 26

[Cu(H2O)6]^2+ = blue sol - blue green precipitate
[Fe(H2O)6]^2+ = green sol - green precipitate
[Fe(H2O)6]^3+ = yellow sol - brown precipitate
[Al(H2O)6]^3+ = colorless sol - white precipitate