AQA A Level Chemistry

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A LevelChemistryAQATopic Questions6. Advanced Inorganic Chemistry (A Level only)6.3 Reactions of Ions in Aqueous Solution (A Level only)

6.3 Reactions of Ions in Aqueous Solution (A Level only)

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11 mark

Which of the following is true about the bonding in metal-aqua ions?

  • Water molecules act as Brønsted-Lowry acids

  • Metal ions act as Brønsted-Lowry bases

  • Water molecules act as Lewis bases

  • Metal ions act as proton acceptors

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21 mark

Which of the following is true about metal-aqua ions?

  • All aqueous transition metal ions are neutral 

  • Transition metal ions with a +2 charge are acidic

  • Deprotonation occurs in all transition metal ions

  • Transition metal ions with a +3 charge are acidic

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31 mark

A white precipitate with some bubbles could be the observations in which of the following reactions?

  • CuCl2 + NH3

  • Al2(SO4)3 + Na2CO3

  • H2SO4 + Na2CO3

  • BaCl2 + Na2SO4

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41 mark

Aqueous iron(II) ions react with ammonia according to the following equation:

[Fe(H2O)6] 3+ (aq)  + 3NH3 (aq) →    Fe(H2O)3(OH)3 (s)  + 3NH4+ (aq)

In this reaction, what is the role of the ammonia?

 

Base

Nucleophile

Ligand

A

✓

✓

✓

B

✓

✓

⨯

C

⨯

✓

✓

D

✓

⨯

⨯

 

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51 mark

Copper(II) nitrate can undergo the following sequence of reactions:

 Cu left parenthesis NO subscript 3 right parenthesis subscript 2 space rightwards arrow with Step space 1 on top space space blue space solution space straight A space rightwards arrow with Step space 2 on top space space blue space precipitate space straight B space rightwards arrow with Step space 3 on top space dark space blue space solution space straight C

The reagents needed to carry out steps 1, 2 and 3 could be

 

Step 1

Step 2

Step 3

A

Excess H2O

Drops of NaOH (aq)

Drops of conc. HCl (aq)

B

Excess H2O

Excess NH3 (aq)

Drops of conc. HCl (aq)

C

Excess H2O

Drops of NH3 (aq)

Excess NH3 (aq)

D

Excess H2O

Drops of NH3 (aq)

Excess H2O

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11 mark

Two possible reactions of hydrated chromium(III) hydroxide are shown below.

6-3-aqa-a-level-chemistry-mcq-q1-hard

Which statement about these reactions is correct?

  • Reaction 1 shows the hydrated chromium(III) hydroxide acting as a Brønsted–Lowry acid

  • Reactions 1 and 2 are examples of ligand substitution reactions

  • Reactions 1 and 2 display the amphoteric nature of hydrated chromium(III) hydroxide

  • Reaction 2 shows the hydrated chromium(III) hydroxide behaving as a Brønsted–Lowry base

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21 mark

Hexa-aqua solutions of transition metals in the +2 oxidation state, [M(H2O)6]2+ (aq), can react with excess aqueous ammonia to form various complexes.

Which of the following statements about these reactions with excess aqueous ammonia is correct?

  • [M(H2O)6]2+ (aq) can form products that exist as stereoisomers

  • [M(H2O)6]2+ (aq) undergo full ligand substitution to form [M(NH3)6]2+ (aq)

  • [M(H2O)6]2+ (aq) forms products with the transition metal in the +3 oxidation state

  • [M(H2O)6]2+ (aq) can form precipitates of [M(H2O)4(NH3)2] (s)

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31 mark

The reactions of three different metal complexes with aqueous sodium hydroxide are shown in the table.

Formula of complex ion

Addition of small amount of NaOH (aq)

Addition of excess NaOH (aq)

[M(H2O)6]2+

Coloured precipitate forms

No further change

[X(H2O)6]3+

Coloured precipitate forms

Precipitate dissolves

[Q(H2O)6]3+

White precipitate forms

Precipitate dissolves

 

Which statement about the metals is most likely to be true?

  • Q is not a transition metal

  • The [M(H2O)6]2+ complex will react with carbonate ions to produce carbon dioxide 

  • [X(H2O)6]3+ forms a precipitate with carbonate ions with the formula XCO3

  • [Q(H2O)6]3+ forms a coloured solution when excess aqueous ammonia is added

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41 mark

The pH of a 1.0 mol dm-3 solution of aluminium chloride is approximately 3, whereas the pH of a 1.0 mol dm-3 solution of iron(II) chloride is approximately 5.

What is the best explanation for this?

  • The Al3+ has a greater charge density than the Fe2+ ion

  • The aluminium chloride solution contains more ions

  • The Al3+ ion has a greater nuclear charge than the Fe2+ ion

  • The aqueous Al3+ ion has a greater coordination number than the Fe2+ ion

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51 mark

Which of the options below shows the correct observation and chemical explanation for the reactions of a solution of iron(II) chloride?

 

 

Substance added (in excess)

Observation

Explanation

A

Na2CO3 (aq)

Green precipitate which redissolves to form a green solution

Carbonate ions act as a base, removing H+ from the water molecules in the complex

B

NH3 (aq)

Green precipitate which redissolves to form a green solution

A ligand exchange reaction occurs  - ammonia displaces

C

Na2CO3 (aq)

Green precipitate which does not redissolve; fizzing

Carbonate ions act as a base, removing H+ from the water molecules in the complex. CO2 gas is also formed.

D

NH3 (aq)

Green precipitate which does not redissolve

Ammonia acts as a base, removing H+ from the water molecules in the complex

 

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11 mark

Iron(III) forms a complex ion [Fe(H2O)6]3+.

What is the role of the water molecule in this species?

  • Brønsted-Lowry acid and Lewis base

  • Brønsted-Lowry base and Lewis base

  • Brønsted-Lowry base only

  • Lewis base only

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21 mark

Transition metal ions with the general formula, M3+, will often undergo hydrolysis reactions in water. One such ion is Fe(III) and the reactant side of the hydrolysis equation is:

 [Fe(H2O)6]3+    +   H2O      ⇌      -------------------      +     -------------------

Which of the following correctly completes the equation?

  • [Fe(H2O)5(OH)]2+    +   H+

  • [Fe(H2O)5(OH)]3+    +   H3O+

  • [Fe(H2O)5(OH)]2+    +   H3O+

  • Fe(H2O)3(OH)3          +  3H+

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31 mark

Which of the following ions produces identical observations when sodium hydroxide or ammonia solutions are added until in excess?

  • [Fe(H2O)6]2+

  • [Al(H2O)6]3+

  • [Cu(H2O)6]2+   

  • [Co(H2O)6]2+

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41 mark

Chelation is the formation of complexes with multidentate ligands.

Which of the following is true about chelation?

  • Stronger bonds are formed between the multidentate ligands and the central metal ions

  • The chelated complexes are more stable due to positive entropy changes

  • The number of entities decreases in chelation which favours the reaction

  • Negative enthalpy changes during chelation favour the reactions

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51 mark

Aqueous iron(III) ions react with sodium carbonate solution.

What happens in the reaction?

 

Observations

Products

A

Brown precipitate

Bubbles of gas

Fe(H2O)3(OH)3

CO2

B

Brown precipitate

-

Fe2(CO3)3

-

C

Orange solution

-

[Fe(H2O)5(OH)]2+

-

D

Brown precipitate

Bubbles of gas

Fe2(CO3)3

CO2

 

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