Exam Q - ions in aq

state a reagent for reaction from Fe3+ to Fe2+

XS Sn

 Solution Y contains two different negative ions. 

To a sample of solution Y in a test tube a student adds 

•   silver nitrate solution 

•   then an excess of dilute nitric acid 

•   finally an excess of concentrated ammonia solution. 

The observations after each addition are recorded in the table. 

  

Reagent added to solution Y	Observation
silver nitrate solution	cream precipitate containing compound D and compound E
excess dilute nitric acid	cream precipitate D and bubbles of  gas F
excess concentrated ammonia solution	colourless solution containing complex ion G

Give the formulas of D, E and F. 

Give an ionic equation to show the formation of E. 

Give an equation to show the conversion of D into G. 

 D AgBr Ignore state symbols 

1 

E Ag₂CO₃ 

1 

F CO₂ 

1 

2 Ag⁺  +  CO₃^2–  →  Ag₂CO₃ 

1 

AgBr  +  2 NH₃  →  Ag(NH₃)₂⁺  +  Br ^– 

Or → Ag(NH₃)₂Br 

One mark for Ag(NH₃)₂⁺ and 1 mark for equation 

If D = AgCl, then allow 2 marks for 

AgCl + 2 NH₃ → Ag(NH₃)₂⁺ + Cl^– 

2 

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. 

___________________________________________________________________ 

(1) 

(b)     Give an equation to show how the complex ion Z can act as a Brønsted–Lowry acid with water. 

(a)     AlCl₃  +  6H₂O  →  [Al(H₂O)₆]³⁺  +  3Cl^– 

Allow 

AlCl₃ + 6H₂O → Al(H₂O)₅(OH)²⁺ + H⁺ + 3Cl^– 

1 

(b)     [Al(H₂O)₆]³⁺  +  H₂O  →  [Al(H₂O)₅(OH)]²⁺  +  H₃O⁺

Solution A contains the compound [Cu(H₂O)₆]

 (a)     An excess of ammonia was added to a sample of solution A to form solution B. 

Write an ionic equation for the reaction that occurs when solution A is converted into solution B and state the colour of solution B

 (a)     [Cu(H₂O)₆ ]²⁺  +  4NH₃  →  [Cu(NH₃)₄(H₂O)₂ ]²⁺  +  4H₂O 

1 

Deep blue / Royal blue / Dark blue (solution) 

   Reagent D was added to another sample of solution A to form a yellow-green solution. 

Identify reagent D and write an ionic equation for the reaction that occurs when the yellow-green solution is formed from solution A. 

Solution A contains the compound [Cu(H₂O)₆]

  HCl / hydrochloric acid 

Allow soluble chloride salt 

Also allow any reagent which leads to a change in colour of solution due to a change in ligands (e.g. NH₂CH₂CH₂NH₂) or change in oxidation state (e.g. SO₂ ) and associated correct equations. 

1 

[Cu(H₂O)₆ ]²⁺  +  4Cl⁻  →  [CuCl₄]²⁻  +  6H₂O 

[Cu(H₂O)₆ ]²⁺  +  4HCl  →  [CuCl₄]²⁻  +  6H₂O  +  4H⁺ 

The following tests were carried out to identify an unknown green salt Y. 

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. 

Another aqueous solution of Y gave a green precipitate B when reacted with sodium carbonate solution. 

The green precipitate 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. 

(a)     Identify by name or formula the compounds A, B, C, D and Y. 

(c)     Write the simplest ionic equation for the reaction that occurs between the green precipitate B and sulfuric acid. 

(a)     A  Silver bromide / AgBr 

1 

B  Iron(II) carbonate / FeCO₃ 

1 

C  Iron(II) sulphate / FeSO₄ 

1 

D  Carbon dioxide / CO₂ 

1 

Y  Iron(II) bromide / FeBr₂ 

(c)     2H⁺  +  CO₃²⁻  ⟶  H₂O  +  CO₂ 

Allow   FeCO₃ + 2H⁺ ⟶ Fe²⁺ + CO₂ + H₂O 

Q6. 

What forms when a solution of sodium carbonate is added to a solution of gallium(III) nitrate? 

A        A white precipitate of gallium(III) carbonate.                        

B        A white precipitate of gallium(III) hydroxide.                        

C        A white precipitate of gallium(III) carbonate and                 
 bubbles of carbon dioxide. 

D        A white precipitate of gallium(III) hydroxide and                  
 bubbles of carbon dioxide. 

d

Which compound gives a colourless solution when an excess of dilute aqueous ammonia is added? 

A        MgCl₂             

B        AgCl              

C        CuCl₂            

D        AlCl₃              

b

What is the final species produced when an excess of aqueous ammonia is added to aqueous aluminium chloride? 

A        [Al(NH₃)₆]³⁺                  

B        [Al(OH)₃(H₂O)₃]          

C        [Al(OH)₄(H₂O)₂]^–         

D        [Al(OH)(H₂O)₅]²⁺         

b

  Describe what you would observe when dilute aqueous ammonia is added dropwise, to excess, to an aqueous solution containing copper(II) ions. 
Write equations for the reactions that occur. 

(a)     Blue precipitate 

1 

Dissolves to give a dark blue solution 

1 

[Cu(H₂O)₆]²⁺  +  2NH₃     Cu(H₂O)₄(OH)₂  +  2NH₄⁺ 

1 

Cu(H₂O)₄(OH)₂  +  4NH₃    [Cu(NH₃)₄(H₂O)₂]²⁺  +  2OH^–  +  2H₂O 

This question is about aqueous ions of the metal iron.

When an aqueous [Fe(H2O)6]3+ ion reacts with ethanedioate ions, an iron(III)

complex ion X is formed.

The only ligands in X are ethanedioate ions.

state the charge.

3-

(b) The formation of X is an example of the chelate effect.

Explain the meaning of the chelate effect.

M1 When bidentate/multidentate ligands replace monodentate ligands (to

form a more stable complex)

M2 Because there is an increase in entropy/positive entropy

change/disorder or more particles formed (so ∆G is negative and ∆H is

approximately 0)

Outline how Fe2+ ions catalyse the reaction between S2O82– ions and I– ions

in aqueous solution.

In your answer you should include

• a sketch graph to show how the concentration of S2O82– ions changes

over time

• an explanation of how Fe2+ ions catalyse the reaction, including

equations

• an overall equation for the reaction.

_____________________________________

1a labelled axes

and concentration (of S2O82- ions) decreasing with

time (ignore units)

1b downwards curve of reducing steepness

stage 2 explanation

2a (reaction slow) because S2O82- and I- repel/high

Ea

OR

(reaction slow) because two negative ions

repel/high Ea

2b Fe2+ attracts the S2O82- so lower Ea

OR

Fe2+ and S2O82- oppositely charged so lower Ea

2c Iron/Fe has a variable oxidation state

OR

Fe2+ oxidised to Fe3+

OR

Fe2+ → Fe3+ + e-

stage 3 equations

3a 2 Fe2+ + S2O82- → 2 SO42- + 2 Fe3+

3b 2 Fe3+ + 2 I-

→ 2 Fe2+ + I2

3c S2O82- + 2 I-

→ 2 SO42- + I2

Allow equations with hexaaqua ions

The student adds sodium carbonate solution to a solution containing

[Fe(H2O)6]2+ ions.

State one observation the student would make.

green ppt

Solution A contains the compound [Cu(H2O)6]Cl2

1. An excess of ammonia was added to a sample of solution A to form solution B.

Write an ionic equation for the reaction that occurs when solution A is

converted into solution B and state the colour of solution B.

[2 marks]

2. Reagent D was added to another sample of solution A to form a yellow-green

   solution.

   Identify reagent D and write an ionic equation for the reaction that occurs when

   the yellow-green solution is formed from solution A.

3. Explain why colorimetry cannot be used to determine the concentration of

   solutions containing [CuCl2]−

   In your answer refer to the electron configuration of the metal ion.

[Cu(H2O)6 ]2+ + 4NH3  [Cu(NH3)4(H2O)2 ]2+ + 4H2O

1

Deep blue / Royal blue / Dark blue (solution)\

HCl/ hydrochloric acid

1

[Cu(H2O)6 ]2+ + 4Cl–  [CuCl4]2– + 6H2O

[Cu(H2O)6 ]2+ + 4HCl  [CuCl4]2– + 6H2O + 4H+

1

07.6 (3)d10 or has full (3)d (sub) shell/orbital It is colourless/cannot absorb (frequencies of) visible light

equation when ALCL3(aq) acts as a brostead lowery acid

[Al(H2O)6]3+ + H2O → [Al(H2O)5(OH)]2+ + H3O+

(e)  [CuCl₄]²⁻  +  6H₂O  →  [Cu(H₂O)₆]²⁺  +  4Cl⁻ 

1 

(f)  deep / dark blue 

1 

[CuCl₄]²⁻  +  4NH₃  +  2H₂O  →  [Cu(NH₃)₄(H₂O)₂]²⁺  +  4Cl⁻ 

Give the formula of the complex ion C.

State one condition needed for the formation of C from [Al(H2O)6]3+(aq) and

NaOH(aq).

Give an equation for this reaction.

[3 marks]

M1 C = [Al(OH)4]– OR [Al(H2O)2(OH)4]– OR [Al(OH)6]3–

M2 Excess NaOH

M3 [Al(H2O)6]3+ + 4 OH–  [Al(OH)4]– + 6 H2O

OR

[Al(H2O)6]3+ + 4 OH–  [Al(H2O)2(OH)4]– + 4 H2O

OR

[Al(H2O)6]3+ + 6 OH–  [Al(OH)6]3– + 6 H2O

Explain, with the use of an equation, why a solution containing [Al(H2O)6]3+ has

a pH ˂7

[3 marks]

M1 [Al(H2O)6]3+ + H2O ⇌ [Al(H2O)5(OH)]2+ + H3O+ OR

[Al(H2O)6]3+ ⇌ [Al(H2O)5(OH)]2+ + H+

Al3+ has a small size and high charge OR has a high charge

Accept other equations

M2 density

M3 M2 Allow the aluminium ion has a small size and

high charge OR has a high charge density

Weakens the OH bond (in water) releasing H+ ions