2.6 Reactions of ions in aqueous solution

Question 1

What happens when Fe2+ reacts with dilute sulphuric acid
- state observation
- state complex ion formed

Answer 1

observation : pale green solution
formula : {Fe(H2O)6}^2+

Question 2

state formula of precipitate and observation when {Fe(H2O)6}^2+ is added to sodium hydroxide
- write equation

Answer 2

observation : green solution turns into a pale green precipitate
formula : Fe(OH)2(H2O)4
equation: Fe(H2O)6]2+ + 2OH- → Fe(H2O)4(OH)2 + 2H2O

Question 3

state formula of precipitate and observation when Fe(OH)2(H2O)4 is allowed to stand in air

Answer 3

observation : brown precipitate
formula : Fe(OH)3(H2O)3

Question 4

what happens when Cu^2+ dissolves in nitric acid
- state observation
- state formula
- write equation

Answer 4

observation : blue solution formed
formula : [Cu(H2O)6]2+

Question 5

what happens when excess concentrated hydrochloric acid is added to [Cu(H2O)6]2+
- state formula
- state observation
- state equation

Answer 5

observation : yellow - green solution
formula : CuCl4^2-
equation : [Cu(H2O)6]2+ + 4Cl^- -> CuCl4^2- + 6H2O

Question 6

what happens when aqueous ammonia is added to [Cu(H2O)6]2+
- state formula
- state observation
- write an equation for its formation
b) do the same for when an excess ammonia is added to the new ion

Answer 6

observation : blue precipitate
formula : Cu(OH)2(H2O)4
equation : Cu(H2O)6 ^2+ + 2NH3 -> Cu(OH)2(H2O)4 + 2NH4^+
b) formula : [Cu(NH3)4(H2O)2]^2+
observation : dark/deep blue solution
equation : Cu(H2O)4(OH)2 + 4NH3 -> Cu(NH3)4(H2O)^2+ 2H2O + 2OH^-

Question 7

what happens when Na2CO3 is added to [Cu(H2O)6]2+ (aq)
- state formula
- state observation
- write an equation for its formation

Answer 7

formula : CuCO3
green precipitate
[Cu(H2O)6]^2+ + CO3^2- -> CuCO3 + 6H2O

Question 8

Copper metal can be extracted from dilute aqueous solution containing copper (ii) ions using scrap ion
- state initial and final colour
- write an equation for its formation

Answer 8

initial : blue
final : green
equation : Cu^2+ (aq) + Fe(s) -> Cu (s) + Fe^2+ (aq)

Question 9

what happens when Na2CO3 is added to [Fe(H2O)6]3+ (aq)
- state initial colour and final observation
- write an equation for its formation

Answer 9

brown solution gives a brown precipitate
effervescence
2[Fe(H2O)6]3+ + 3CO3^2– → 2Fe(H2O)3(OH)3 + 3CO2 + 3H2

Question 10

what happens when Na2CO3 is added to [Al(H2O)6]3+ (aq)
- state observation
- write an equation for its formation

Answer 10

white precipitate
effervescence
2[Al(H2O)6]^3+ + 3CO3^2- -> 2[Al(H2O)3(OH)3] + 3CO2 + 3H2O

Question 11

what happens when Na2CO3 is added to [Fe(H2O)6]2+ (aq)
- state initial colour and final observation
- write an equation for its formation

Answer 11

green solution gives a green precipitate
[Fe(H2O)6]2+ + CO32− → FeCO3 + 6H2O

Question 12

what happens when excess concentrated HCl is added to [Co(H2O)6]^2+
- state initial colour and final observation
- write an equation for its formation

Answer 12

pink solution turns into a brown solution
[Co(H2O)6]2+ + 4Cl− → [CoCl4]^2− + 6H2O

Question 13

what happens when dilute aqueous ammonia is added to [Al(H2O)6]3+ (aq)
- state observation
- write an equation for its formation

Answer 13

colourless solution gives a white precipitate
[Al(H2O)6]3+ + 3NH3 → Al(H2O)3(OH)3 + 3NH4

Question 14

what happens when dilute aqueous ammonia is added to [Ag(H2O)2]^+
- state observation
- write an equation for its formation

Answer 14

no visible change as colourless solution remains a colourless solution
[Ag(H2O)2]+ + 2NH3 → [Ag(NH3)2]+ + 2H2

Question 15

what forms with NaOH and Na2CO3 to form a white precipitate

Answer 15

Calcium & magnesium

Question 16

What is formed when aluminium reacts with NaOH and Na2CO3

Answer 16

NaOH : white precipitate, dissolves in NaOH
Na2CO3 : white precipitate, bubbles of gas

Question 17

An aqueous solution of Y gave a cream precipitate of Compound A when reacted with silver nitrate solution
Compound A gave a colourless solution when reacted with concentrated ammonia solution
Identify A

Answer 17

Silver bromide

Question 18

Aqueous solution of Y gave a green precipitate B when reacted with sodium carbonate
- Identify B & write the simplest ionic equation that occurs when green precipitate B and sulfuric acid react
green precipitate of B was filtered and dried and then reacted with sulfuric acid to give a pale green solution containing compound C and a colourless gas D
Identify C and D

Answer 18

B: FeCO3 Iron (ii) carbonate
equation : 2H+ + CO3^2- -> H2O + CO2
C: Iron (ii) sulphate FeSO4
D: CO2

Question 19

Solution A contains the compound [Cu(H2O)6]Cl2
State the type of bonding between the oxygen and hydrogen in this compound.
b) state why chloride ions in this compound are not considered to be ligands

Answer 19

Covalent bonding
b) they are not donating a lone pair to the metal ion
and it doesn’t form a coordinate bond to the metal ion

Question 20

what is a complex ion

Answer 20

A complex ion is a positive metal ion surrounded by ligands. The ligands bond to the central metal ion by co-ordinate bonds

Question 21

define a coordinate bond

Answer 21

a coordinate bond is a shared pair of electrons which have both come from the same atom

Question 22

define a ligand

Answer 22

A Ligand is an ion or molecule with a lone pair of electrons which can form a coordinate bond with a metal ion

Question 23

what is the coordination number

Answer 23

the number of coordinate bonds a transition metal ion forms

Question 24

what happens when an excess of ammonia is added to [Cu(H2O)6]Cl2
- state observation
- write an equation for its formation

Answer 24

Cu(H2O)4(OH)2 + 4NH3 -> Cu(NH3)4(H2O)^2+ 2H2O + 2OH^-
deep blue solution formed

Question 25

When anhydrous aluminium chloride reacts with water, solution Y is formed that contains a complex aluminium ion, Z, and chloride ions. Give an equation for this reaction. b) Give an equation to show how the complex ion Z can act as a Brønsted–Lowry acid with water.

Answer 25

AlCl3 + 6H2O -> [Al(H2O)6]^3+ + 3Cl b) [Al(H2O)6]^3+ + H2O -> [Al(H2O)5(OH)]2+ + H2O^-

Question 26

state the colour of a) [Cu(H2O)6]2+ b) [Fe(H2O)6]2+ c) [Fe(H2O)6]3+ d) [Al(H2O)6]3

Answer 26

a) Blue solution Pale b) green solution c) Yellow brown solution d) Colourless solution

Question 27

write equation of Fe(III) complex acting as an acid

Answer 27

Fe(H2O)6]3+ → [Fe(H2O)5(OH)]2+ + H+

Question 28

Aqueous potassium hydroxide is added, until in excess, to [Al(H2O)6]^3+ Describe two observations you would make. For each observation give an equation for the reaction that occurs.

Answer 28

Observation 1 : colourless solution to white precipitate equation 1 : Al(H2O)6]3+ + 3OH- → [Al(H2O)3(OH)3](s) + 3H2O observation 2: White precipitate dissolves to form a colourless solution equation 2 : [Al(H2O)3(OH)3](s) + OH- → [Al(H2O)2(OH)4]- + H2O

Question 29

state what is observed and give equation for when [Fe(H2O)6]^2+ reacts with Na2CO3

Answer 29

Observation : green solution to green precipitate equation : Fe(H2O)6]2+ + CO32- → FeCO3(s) + 6H2O

Question 30

state what is observed and give equation for when [Fe(H2O)6]^2+ reacts with NH3

Answer 30

Observation : green solution turns into green precipitate equation : [Fe(H2O)6]2+ + 2NH3 → [Fe(H2O)4(OH)2](s) + 2NH4+

Question 31

reagent to turn [Fe(H2O)6]^3+ -> [Fe(H2O)6]^2+

Answer 31

Excess H2SO4

Question 32

why, with use of an equation., a solution containing [Al(H2O)6]^3+ has a pH less than 7

Answer 32

Al(H2O)6]3+ ⇌ [Al(H2O)5(OH)]2+ + H+ Al3+ has a small size and high charge Weakens the OH bond (in water) releasing H+ ions

Question 33

Explain why an aqueous solution containing [Fe(H2O)6]3+ ions has a lower pH than an aqueous solution containing [Fe(H2O)6]2+ ions.

Answer 33

- [Fe(H2O)6]^3+ has a higher charge and is smaller - Fe^3+ is more polarising as it polarises water molecules more - more OH bonds in the water ligands break and hence more OH^+ ions are released

Question 34

When anhydrous aluminium sulphate, Al2(SO4)3, is added to water a solution forms that contains the complex aluminium ion, [Al(H2O)6]3+Give the equation for the reaction

Answer 34

Al2(SO4)3 + 12 H2O → 2 [Al(H2O)6]3+ + 3 SO42-

Question 35

Explain why the solution containing [Al(H2O)6]3+ is acidic

Answer 35

Al3+ has a high charge and small size Al3+ weakens the O-H bond (in water ligands and donates H+ to water or forms H3O+ ions with water

Question 36

Which aqueous-ion solutions are the most acidic

Answer 36

[Fe(H20)6]^3+ & [Al(H20)]^3+

Question 37

Why are solutions of [Al(H2O)6]3+ and [Fe(H2O)6]3+ more acidic than solutions of [CuH2O)6]2+ and [Fe(H2O)6]2+?

Answer 37

Al3+ and Fe3+ are smaller and have a higher charge than Cu2+ and Fe2+. Al3+ and Fe3+ polarise the water ligands more than Cu2+ and Fe2+, so the weaken the O−H bonds more (and dissociate more H+)

Question 38

Answer 38

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Question 39

Answer 39