2.6 Reactions of Ions In Aqueous Solution

Question 1

Are 2+ ions or 3+ ions more acidic in solution? Why?

Answer 1

3+ ions are much more acidic

3+ ions are smaller and more highly charged, so have a higher charge density. They attract the electrons from the oxygen of the ligands much more strongly. This weakens the O-H bonds, so the complex readily releases a H+ ion into the solution, making it acidic

Question 2

Write an equation for the hydrolysis of a 3+ ion to release a proton

Answer 2

[Fe(H2O)6]3+ (aq) ⇌ [Fe(H2O)5(OH)]2+ (aq) + H+ (aq)

Question 3

What kind of acid is the complex ion acting as? Why?

[Fe(H2O)6]3+ (aq) ⇌ [Fe(H2O)5(OH)]2+ (aq) + H+ (aq)

Answer 3

Bronsted-Lowry - donates a proton

Question 4

Define a Lewis acid

Answer 4

Electron pair acceptor

Question 5

Define a Lewis base

Answer 5

Electron pair donor

Question 6

What is acting as the Lewis acid and what is acting as the Lewis base during the formation of complex ions?

Answer 6

The metal ion is acting at the Lewis acid and the ligands as Lewis bases

Question 7

Fill in the table for Fe2+ reactions

Answer 7

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Question 8

Why does the green ppt go brown on standing in air in the reaction of Fe2+ with NH3?

Answer 8

Oxygen in the air oxidises Fe2+ to Fe3+, and [Fe(OH)3(H2O)3] is brown, so colour changes

Question 9

Fill in the table for the reactions of Cu2+

Answer 9

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Question 10

Fill in the table for the reactions of Fe3+

Answer 10

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Question 11

Fill in the table for the reactions of Al3+

Answer 11

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Question 12

Fill in the table for the reactions of CO2+

Answer 12

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