Reactions of ions in aqueous solution

Question 1

are metal aqua ions acidic or alkaline in solution?

Answer 1

acidic

Question 2

what affects how acidic the solution of metal aqua ions formed is?

Answer 2

the charge on the ion: higher charge = more acidic in solution

Question 3

what is H3O+?

Answer 3

a hydronium ion

Question 4

what happens to 2+ complexes in water?

Answer 4

they dissociate weakly so are not very acidic

Question 5

what happens to 3+ complexes in water?

Answer 5

they dissociate more readily than 2+ complexes so are more acidic

Question 6

why are 3+ complexes more acidic than 2+ complexes when in solution?

Answer 6

3+ complex ions have a higher charge density so are more polarising than 2+ ions - they attract electrons in the O-H bond in the water ligands more strongly, which weakens the bond - so it is more likely that the H+ ion will be released

Question 7

how can you further hydrolyse metal-aqua ions?

Answer 7

using OH- ions
the OH- ions remove H+ and cause the eqm. that was previously established with hydrolysis to shift right

Question 8

at happens when you add water to metal-aqua ions

Answer 8

they are hydrolysed and an eqm. is established

Question 9

what does the further hydrolysis of metal-aqua ions eventually lead to?

Answer 9

the formation of a neutral complex that is solid and so forms a ppt. in solution

Question 10

how many steps are there in the continuous hydrolysis of metal-aqua 3+ ions?

Answer 10

3

e.g. M(H2O)3(OH)3 (s)

Question 11

how many steps are there in the continuous hydrolysis of metal-aqua 2+ ions? why?

Answer 11

2
because only 2 water ligands need to be deprotonated to form a neutral complex

e.g. M(H2O)4(OH)2 (s)

Question 12

what is special about aluminium hydroxide [Al(H2O)3(OH)3]?

Answer 12

it is amphoteric

Question 13

what happens when ammonia is added to metal-aqua ions?

Answer 13

they form metal hydroxides

Question 14

what can sometimes happen when excess ammonia is added to metal-aqua ions?

Answer 14

ligand-substitiution reactions

Question 15

how does ammonia exist in solution?

Answer 15

NH3 + H2O ⇌ NH4+ + OH-

Question 16

what happens when excess ammonia is added to [Cu(OH)2(H2O)4]?

Answer 16

partial ligand substitution:
[Cu(OH)2(H2O)4] + 4NH3 ⇌ [Cu(NH3)4(H2O)2]2+ + 2OH- + 2H2O

Question 17

what does adding sodium carbonate to 2+ metal-aqua ions form?

Answer 17

metal carbonates precipitates
e.g. [M(H2O)6]2+ + CO32- ⇌ MCO3 + 6H2O
(complete substitution of all the water ligands)

Question 18

what does adding sodium carbonate to 3+ metal-aqua ions form? why?

Answer 18

[M(OH)3(H2O)3] ppt. because the ions are more acidic so the carbonate ions react with the H+ ions instead of displacing the water ligands

note that carbon dioxide is also produced so fizzing is seen

Question 19

how can you identity metal ion solutions?

Answer 19

by reacting them with NH3, NaOH and Na2CO3 and observing what happens

Question 20

which 4 metal-aqua ions need to be learnt?
(and the test-tube reactions known)

Answer 20

[Fe(H2O)6]2+
[Cu(H2O)6]2+

[Al(H2O)6]3+
[Fe(H2O)6]3+

Question 21

which metal-aqua ion dissolves in excess NaOH?

Answer 21

[Al(H2O)6]3+

Question 22

how do you carry out the test tube reactions?

Answer 22

add a small amount of reagent and observe, then add it in excess and observe (only one of them should redissolve but they will all initially form a ppt.)

Question 23

which metal-aqua ion dissolves in excess NH3?

Answer 23

[Cu(H2O)6]2+

Question 24

which metal-aqua ions will produce fizzing (CO2) when they react with Na2CO3?

Answer 24

[Al(H2O)6]3+
[Fe(H2O)6]3+

Question 25

what happens when Fe2+ reacts with air?

Answer 25

it oxides to form Fe3+

Question 26

what formula do metal ions dissolved in water have?

Answer 26

[M(H2O)6]n+ (metal-aqua ions)
can be simplified to Mn+
where M = metal

Question 27

colour of [Cu(H2O)6]2+
a.k.a Cu2+ (aq.)

Answer 27

blue (aq.)

Question 28

colour of [Cu(OH)2(H2O)4]

Answer 28

pale blue precipitate

Question 29

colour of [Cu(NH3)4(H2O)2]2+

Answer 29

dark blue (aq.)

Question 30

colour of CuCo3

Answer 30

green-blue precipitate

Question 31

colour of [Fe(H2O)6]2+
a.k.a Fe2+ (aq.)

Answer 31

pale green (aq.)

Question 32

colour of [Fe(OH)2(H2O)4]2+

Answer 32

green precipitate

Question 33

colour of FeCO3

Answer 33

green precipitate

Question 34

colour of [Fe(H2O)6]3+
a.k.a Fe3+ (aq.)

Answer 34

yellow (aq.)

Question 35

colour of [Fe(OH)3(H2O)3]

Answer 35

brown precipitate

Question 36

colour of [Fe(OH)3(H2O)3] (from addition of Na2CO3)

Answer 36

brown precipitate

Question 37

colour of [Al(H2O)6]3+
a.k.a Al3+ (aq.)

Answer 37

colourless

Question 38

colour of [Al(OH)3(H2O)3]

Answer 38

white precipitate