Reactions Of Ions In Aqeuous Solutions

Question 1

In aqueous solutions what ions are formed with

Fe^2+

Cu^2+

Al^3+

Fe^3+

Answer 1

[Fe(H2O)6]^2+

[Cu(H2O)6]^2+

[Al(H2O)6]^3+

[Fe(H2O)6]^3+

Question 2

Explain when aqueous ions of [M(H2O)6]^3+ have a higher acidity that [M(H2O)6]^2+

Answer 2

This is because M^3+ ion complexes are larger and have a higher charge therefore having a stronger polarising power.

This means that the oxygen atoms in the water ligands are more strongly attracted to the M^3+ ions.

This therefore weakens the OH bonds meaning H+ ions are lost more easily and hence the solution is more acidic.

Question 3

Define amphoteric?

Answer 3

A species that shows both acidic and basic properties

Question 4

Explain the amphoteric properties of Aluminium hydroxide.

Answer 4

Although aluminium hydroxide is not a transition metal, it forms aqua ions.

With acid (HCL):

[Al(H2O)3(OH)3] + 3HCl ——> [Al(H2O)6]^3+ + 3Cl^-

With base (NaOH):

[Al(H2O)3(OH)3] + OH^- ——> [Al(OH)4]^- + 3H2O

Question 5

Describe and explain (using equations) what happens when aqueous solution of [Fe(H2O)6]^2+ has the addition of

NaOH

NaOH (excess)

NH3

NH3 (excess)

Na2CO3

Answer 5

NaOH:
[Fe(H2O)6]^2 + NaOH ——> Fe(H2O)4(OH)2
Goes from green solution to form a dark green ppt which goes brown when standing in air

NaOH (excess):
No further change

NH3:
[Fe(H2O)6]^2 + NH3 ——> Fe(H2O)4(OH)2
Goes from green solution to form a dark green ppt which goes brown when standing in air

NN3 (excess):
No further change

Na2CO3:
[Fe(H2O)6]^2 + Na2CO3 ——> FeCO3
Goes from green solution to form a light green ppt

Question 6

Describe and explain (using equations) what happens when aqueous solution [Cu(H2O)6]^2+ has the addition of

NaOH

NaOH (excess)

NH3

NH3 (excess)

Na2CO3

HCl

Answer 6

NaOH:
[Cu(H2O)6]^2+ + NaOH ——> [Cu(H2O)4(OH)2]^2+
Goes from dark blue solution to form a light blue ppt

NaOH (excess):
No further change

NH3:
[Cu(H2O)6]^2+ + 2NH3 ——> [Cu(H2O)4(OH)2]+ + 2NH4^+
Goes from a dark blue solution to a light blue ppt

NH3 (excess):
[Cu(H2O)4(OH)2]^2+ + 4NH3 ——> [Cu(NH3)4(H2O)2]^2+ + 4H2O
Goes from blue solution to a deep blue solution

Na2CO3:
[Cu(H2O)6]^2+ Na2CO3 ——> CuCO3
Goes from a blue solution to a blue-green ppt

HCl:
[Cu(H2O)6]^2 +HCl ——> [Cu(Cl)4]^2-
Goes form a blue solution to form a yellow solution

Question 7

Describe and explain (using equations) what happens when aqueous solution [Fe(H2O)6]^3+ has the addition of

NaOH

NaOH (excess)

NH3

NH3 (excess)

Na2CO3

Answer 7

NaOH:
[Fe(H2O)6]^3+ + NaOH ——> [Fe(H2O)3(OH)3]
Goes from a purple solution to a brown ppt

NaOH (excess):
No further change

NH3:
[Fe(H2O)6]^3+ + NH3 ——> [Fe(H2O)3(OH)3]
Goes from a purple solution to a brown ppt

NH3 (excess):
No further change

Na2CO3:
[Fe(H2O)6]^3+ + Na2CO3 ——> [Fe(H2O)3(OH)3]
Goes from a purple solution to a brown ppt and CO2 gas evolved

Question 8

Describe and explain (using equations) what happens when aqueous solution [Al(H2O)6]^3+ has the addition of

NaOH

NaOH (excess)

NH3

NH3 (excess)

Na2CO3

Answer 8

NaOH:
[Al(H2O)6]^3+ + NaOH ——> [Al(H2O)3(OH)3]
Goes from a colourless solution to a white ppt

NaOH (excess):
[Al(H2O)3(OH)3] + NaOH ——> [Al(OH)4]^-
Forms a colourless solution

NH3:
[Al(H2O)6]^3+ + NH3 ——> [Al(H2O)(OH)3]
Goes from a colourless solution to form a white ppt

NH3 (excess):
No further change

Na2CO3:
[Al(H2O)6]^3+ + Na2CO3 ——> [Al(H2O)3(OH)3]
Goes from a colourless solution to form a white ppt and CO2 has evolved

Question 9

Describe and explain (using equations) what happens when aqueous solution [Co(H2O)6]^2+ has the addition of

NaOH

NH3 (excess)

Na2CO3

HCl

Answer 9

NaOH:
[Co(H2O)6]^2+ + NaOH ——> [Co(H2O)4(OH)2]
Goes from a pink solution to form a blue ppt

NH3 (excess):
[Co(H2O)6]^2+ + NH3 ——> [Co(NH3)6]^2+
Goes from a pink solution to form a pale brown solution

Na2CO3:
[Co(H2O)6]^2+ + Na2CO3 ——> CoCO3
Goes from a pink solution to form a purple ppt

HCl:
[Co(H2O)6]^2+ + HCl ——> [Co(Cl)4]^2-
Goes from a pink solution to form a blue solution

Question 10

What is the test for positive ions?

Answer 10

Look at precipitation reactions for positive transition metal ions.

Half full a test tube and add ammonia or NaOH drop by drop

Observe colour change of precipitates formed

Add excess for more information

Question 11

What is the test for ammonium ions?

Answer 11

Ammonium ions react with NaOH to produce ammonia

NH4+ + OH- ——> NH3 + H2O

If distinctive smell is produced and damp red litmus paper then blue then solution has ammonium ions

Question 12

How do you find negative ions?

Answer 12

Carry out 3 tests

1. Carbonate test
2. Sulphate test
3. Halide test

Carries out in this order as the carbonates and sulphates may give positive tests for one another

Question 13

How do you test for carbonate ions?

Answer 13

Add an aqueous acid to suspected solution and if CO2 has is produced the. Carbonate ions are present

Test gas by bubbling through lime water and if goes cloudy white then the gas is CO2

Question 14

What do you test for sulphate ions?

Answer 14

Acidify test solution with HCl

Add a few drops of barium chloride to the solution

A white precipitate is formed if sulphate ions are present.

Question 15

What is the test for halide ions?

Answer 15

Add dilute nitric acid and aqueous silver nitrate solution

A precipitate of silver halide ions will form if chloride bromide or iodide is present

Question 16

Explain why carbonate ions react with Cu/Fe 2+ ions to produce a precipitate of a metal carbonate where as they react with Al/Fe 3+ producing metal hydroxides?

Answer 16

M3+ is more acidic than M2+ due to a greater charge density.
This means that H+ ions from the M3+ solution react with the carbonate to liberate carbon dioxide and form the metal Hydroxide.