Inorganic Unit 2.6: Reactions of Ions in Aqueous Solution

Question 1

define metal aqua ions

Answer 1

central metal ion with 6 water ligands

Question 2

when are metal aqua ions present?

Answer 2

when salts are crystallised from solution

Question 3

define hydrolysis

Answer 3

loss of H+ from H2O ligands (O-H bond in H2O ligand breaks)
(‘spontaneous’)

Question 4

define substitution

Answer 4

replacement of H2O by other ligands (metal-ligand bond breaks)
= ligand exchange

Question 5

define redox

Answer 5

metal changes oxidation state (gain or loss of e-s)

Question 6

what are the metal aqua ions of Cu2+, Fe2+, Fe3+ & Al3+ & their colours?

Answer 6

[Cu(H2O)6]2+ blue solution
[Fe(H2O)6]2+ green solution
[Fe(H2O)6]3+ purple solution (may look yellow-brown due to some [Fe(H2O)5(OH)]2+ formed by hydrolysis)
[Al(H2O)6]3+ colourless solution

Question 7

what are the equations for hydrolysis of M2+ aqua ions?

Answer 7

see booklet
neutral complexes are solid

Question 8

what are the equations for hydrolysis of M3+ aqua ions?

Answer 8

see booklet
neutral compounds are solid

Question 9

how is the equilibrium of hydrolysis reactions shifted right & left?

Answer 9

right: add base/OH- to remove H+ = deprotonation

left: add acid H+

Question 10

neutral complex ions

Answer 10

insoluble in water
solid ppts
known as metal(II) hydroxides or metal (III) hydroxides

Question 11

describe the trend in acidity/pH of solutions of aqueous metal ions

Answer 11

as charge on metal in metal aqua ion increases, ion gets smaller so acidity increases so pH decreases

Question 12

what are the main species in solution & in water?

Answer 12

in solution, metal aqua ions lose H+ from H2O ligands

in water, the main species present is [M(H2O)6]n+, but some hydrolysis happens so solution is acidic

Question 13

explain the trend in pH of solutions of metal aqua ions

Answer 13

as the charge on metal aqua ion increases & size decreases, the pH decreases

metal ion with higher charge & smaller
pulls e-s in co-ordinate bond more strongly
so e-s pulled more strongly towards the O
which weakens O-H bond
so O-H is easier to break
H+ released so increased [H+] in solution
so pH decreases

Question 14

some metal hydroxides show amphoteric character

Answer 14

by dissolving in both acids & bases
e.g. hydroxides of Al3+

Question 15

describe the reaction of metal aqua ions with bases

Answer 15

hydrolysis/deprotonation
the base removes H+ pushing the equilibria right
common bases: NH3, OH-, CO32-
forms insoluble, neutral complex ppt

adding XS base = ligand eXchange
insoluble complex reacts further

Question 16

what are the observations & equations for the reaction of [Fe(H2O)6]2+ with dropwise NaOH & XS NaOH?

Answer 16

with dropwise OH-: green solution –> green ppt
[Fe(H2O)6]2+ (aq) + 2OH-(aq) –> Fe(H2O)4(OH)2 + 2H2O(l)

with XS OH-: nvc

Question 17

what are the observations & equations for the reaction of [Cu(H2O)6]2+ with dropwise NaOH & XS NaOH?

Answer 17

with dropwise OH-: blue solution –> blue ppt
[Cu(H2O)6]2+(aq) + 2OH-(aq) –> Cu(H2O)4(OH)2 + 2H2O(l)

with XS OH-: nvc

Question 18

what are the observations & equations for the reaction of [Fe(H2O)6]3+ with dropwise NaOH & XS NaOH?

Answer 18

with dropwise OH-: pale violet solution –> brown ppt
[Fe(H2O)6]3+(aq) + 3OH-(aq) –> Fe(H2O)3(OH)3 + 2H2O(l)

with XS OH-: nvc

Question 19

what are the observations & equations for the reaction of [Al(H2O)6]3+ with dropwise NaOH & XS NaOH?

Answer 19

with dropwise OH-: colourless solution –> white ppt
[Al(H2O)6]3+(aq) + 3OH-(aq) –> Al(H2O)3(OH)3 + 3H2O(l)

with XS OH-: white ppt –> colourless solution
Al(H2O)3(OH)3 + OH-(aq) –> [Al(H2O)2(OH)4]-(aq) + H2O(l)

Question 20

what are the observations & equations for the reaction of [Fe(H2O)6]2+ with dropwise NH3 & XS NH3?

Answer 20

with dropwise NH3: green solution –> green ppt
[Fe(H2O)6]2+(aq) + 2NH3(aq) –> Fe(H2O)4(OH2) + 2NH4+(aq)

with XS NH3: nvc

Question 21

what are the observations & equations for the reaction of [Cu(H2O)6]2+ with dropwise NH3 & XS NH3?

Answer 21

with dropwise NH3: blue solution –> blue ppt
[Cu(H2O)6]2+(aq) + 2NH3(aq) –> Cu(H2O)4(OH)2 + 2NH4+(aq)

with XS NH3: blue ppt –> deep blue solution
Cu(H2O)4(OH)2 + 4NH3(aq) –> [Cu(H2O)2(NH3)4]2+(aq) + 2OH- + 2H2O

Question 22

what are the observations & equations for the reaction of [Fe(H2O)6]3+ with dropwise NH3 & XS NH3?

Answer 22

with dropwise NH3: pale purple solution –> brown ppt
[Fe(H2O)6]3+(aq) + 3NH3(aq) –> Fe(H2O)3(OH)3 + 3NH4+(aq)

with XS NH3: nvc

Question 23

what are the observations & equations for the reaction of [Al(H2O)6]3+ with dropwise NH3 & XS NH3?

Answer 23

with dropwise NH3: colourless solution –> white ppt
[Al(H2O)6]3+(aq) + 3NH3(aq) –> Al(H2O)3(OH)3 + 3NH4+(aq)

with XS NH3: nvc

Question 24

dropwise
XS

Answer 24

deprotonation/hydrolysis
ligand eXchange

Question 25

what is the observation & equation for the reaction of [Fe(H2O)6]2+ with dropwise Na2CO3?

Answer 25

green solution --> green ppt [Fe(H2O)6]2+(aq) + CO32- --> FeCO3(s) + 6H2O precipitation reaction, not deprotonation

Question 26

what is the observation & equation for the reaction of [Cu(H2O)6]2+ with dropwise Na2CO3?

Answer 26

blue solution --> blue-green ppt [Cu(H2O)6]2+(aq) + CO32- --> CuCO3(s) + 6H2O precipitation

Question 27

what is the observation & equation for the reaction of [Fe(H2O)6]3+ with dropwise Na2CO3?

Answer 27

pale purple solution --> brown ppt & effervescence 2[Fe(H2O)6]3+(aq) + 3CO32- --> 2[Fe(H2O)3(OH)3](s) + 3CO2 + 3H2O hydrolysis/deprotonation/acid-base reaction

Question 28

what is the observation & equation for the reaction of [Al(H2O)6]3+ with dropwise Na2CO3?

Answer 28

colourless solution --> white ppt & effervescence 2[Al(H2O)6]3+(aq) + 3CO32- --> 2[Al(H2O)3(OH)3](s) + 3CO2 + 3H2O hydrolysis/deprotonation/acid-base reaction

Question 29

summary of reactions of metal aqua ions & Na2CO3

Answer 29

metal(II) aqua ions react to form ppt of metal (II) carbonates by precipitation metal(III) aqua ions react to form bubbles of CO2 gas & ppt of metal(III)hydroxides by hydrolysis

Question 30

why do metal(II) aqua ions & metal(III) aqua ions react differently with Na2CO3?

Answer 30

[M(H2O)6]3+ is acidic enough to react in an acid base-reaction with CO32- ions by hydrolysis, but [M(H2O)6]2+ is not acidic enough + explanation for acidity

Question 31

what are the observations & equations for the reaction of [Fe(H2O)4(OH)2] with XS acid & XS alkali?

Answer 31

with XS acid: green ppt --> green solution [Fe(H2O)4(OH)2] + 2H+ --> [Fe(H2O)6]2+ with XS alkali: nvc

Question 32

what are the observations & equations for the reaction of [Cu(H2O)4(OH)2] with XS acid & XS alkali?

Answer 32

with XS acid: blue ppt --> blue solution [Cu(H2O)4(OH)2] + 2H+ --> [Cu(H2O)6]2+ with XS alkali: nvc

Question 33

what are the observations & equations for the reaction of [Fe(H2O)3(OH)3] with XS acid & XS alkali?

Answer 33

with XS acid: brown ppt --> pale purple solution [Fe(H2O)3(OH)3] + 3H+ --> [Cu(H2O)6]3+ with XS alkali: nvc

Question 34

what are the observations & equations for the reaction of [Al(H2O)3(OH)3] with XS acid & XS alkali?

Answer 34

with XS acid: white ppt --> colourless solution [Al(H2O)3(OH)3] + 3H+ --> [Al(H2O)6]3+ with XS alkali: white ppt --> colourless solution [Al(H2O)3(OH)3] + OH- --> [Cu(H2O)2(OH)4]- + H2O

Question 35

define & give examples of: acidic hydroxide amphoteric hydroxide basic hydroxide

Answer 35

acidic hydroxide: hydroxide that only reacts with bases amphoteric hydroxide: hydroxide that reacts with both acids & bases e.g. [Al(H2O)3(OH)3] basic hydroxide: hydroxide that only reacts with acids e.g. [Fe(H2O)4(OH)2] [Cu(H2O)4(OH)2] [Fe(H2O)3(OH)3]

Question 36

what are the observations & equations for the reaction of [Fe(H2O)6]2+, [Cu(H2O)6]2+, [Fe(H2O)6]3+ & [Al(H2O)6]3+ with similar sized ligands e.g. XS NH3(aq)

Answer 36

[Fe(H2O)6]2+, [Fe(H2O)6]3+ & [Al(H2O)6]3+ same as for dropwise NH3 [Cu(H2O)6]2+: blue solution --> deep blue solution [Cu(H2O)6]2+ + 4NH3 --> [Cu(H2O)2(OH)4]2+ + 4H2O ligand substitution

Question 37

what is the observation & equation for the reaction of [Fe(H2O)6]2+ with larger ligands e.g. conc. HCl to provide XS Cl-?

Answer 37

green solution --> yellow solution [Fe(H2O)6]2+ + 4Cl- --> [FeCl4]2- + 6H2O

Question 38

what is the observation & equation for the reaction of [Cu(H2O)6]2+ with larger ligands e.g. conc. HCl to provide XS Cl-?

Answer 38

blue solution --> yellow solution (may appear green) [Cu(H2O)6]2+ + 4Cl- --> [CuCl4]2- + 6H2O

Question 39

what is the observation & equation for the reaction of [Fe(H2O)6]3+ with larger ligands e.g. conc. HCl to provide XS Cl-?

Answer 39

pale purple solution --> yellow solution [Fe(H2O)6]3+ + 4Cl- --> [FeCl4]- + 6H2O

Question 40

what is the observation & equation for the reaction of [Al(H2O)6]3+ with larger ligands e.g. conc. HCl to provide XS Cl-?

Answer 40

nvc/colourless solution --> colourless solution [Al(H2O)6]3+ + 4Cl- --> [AlCl4]- + 6H2O

Question 41

summary of substitution reactions with larger ligands

Answer 41

metal aqua ions react with conc. HCl by substitution all 6 H2O ligands are replaced by 4 Cl- ligands

Question 42

what is the colour of the cobalt hexaqua ion? what is the cobalt species & its colour formed from substitution reactions with: NaOH XS NH3(aq) Na2CO3(aq) conc. HCl(aq)?

Answer 42

[Co(H2O)6]2+ pink solution NaOH: [Co(H2O)4(OH)2](s) blue ppt XS NH3(aq): [Co(NH3)6]2+(aq) pale brown solution that darkens on exposure to air Na2CO3(aq): CoCO3(s) purple ppt conc. HCl(aq): [CoCl4]2-(aq) blue solution