4.3.2

Identification (A2 Only)

Test yourself

Precipitates

Precipitates can form with ammonia solution and with carbonates. They are different precipitates to those you get with sodium hydroxide ions.

Illustrative background for Ammonia precipitatesIllustrative background for Ammonia precipitates ?? "content

Ammonia precipitates

  • Ammonia is a base.
    • When you add it to water, you get a reaction according to the following equation:
    • NH3(aq) + H2O(l) ⇌ NH4+(aq) + OH-(aq)
    • The OH-(aq) ions will deprotonate the water ligands and generate an insoluble metal hydroxide precipitate.
Illustrative background for Ammonia ligandsIllustrative background for Ammonia ligands ?? "content

Ammonia ligands

  • If you add a small amount of ammonia, you get the same as with sodium hydroxide.
  • If you add an excess of ammonia, you can get a ligand exchange reaction.
    • The ammonia can replace some of the water ligands and some of the hydroxide ligands.
  • This happens for the reaction with [Cu(H2O)6]2+.
    • The reaction with excess ammonia is:
    • [Cu(H2O)6]2+(aq) + 4NH3(aq) → [Cu(H2O)2(NH3)4]2+(aq)
Illustrative background for Carbonate reactionsIllustrative background for Carbonate reactions ?? "content

Carbonate reactions

  • M2+ ions react with sodium carbonate according to the following equation:
    • [M(H2O)6]2+(aq) + CO32-(aq) ⇌ MCO3(s) + 6H2O(l)
Illustrative background for M<sup>3+</sup> ions and carbonatesIllustrative background for M<sup>3+</sup> ions and carbonates ?? "content

M3+ ions and carbonates

  • M3+ ions are stronger acids. This means they react with the carbonates in a different way.
    • They release H+ ions which react with the carbonate ions:
    • CO32-(aq) + 2H+(aq) → H2O(l) + CO2(g)
    • In practice, this means that the carbonates act as bases. You get the same product as for hydroxide with M3+ ions.

Test Tube Reactions

To identify a metal ion, you can test its behaviour with hydroxide, ammonia, and carbonates in a test tube.

Illustrative background for ProcedureIllustrative background for Procedure ?? "content

Procedure

  • To test your ions, you want to put a small sample in three test tubes:
    • To the first, add sodium hydroxide and record any changes. Then add sodium hydroxide to excess to see if anything changes.
    • To the second, repeat the process with ammonia.
    • To the third, add some sodium carbonate.
  • In the following slides, we’ll see how to tell the difference between copper(II), iron(II), iron(III) and aluminium(III).
Illustrative background for Sodium hydroxideIllustrative background for Sodium hydroxide ?? "content

Sodium hydroxide

  • The four ions will all form precipitates with sodium hydroxide.
    • When you add excess sodium hydroxide to aluminium(III), it will re-dissolve because [Al(OH)4]−(aq) forms.
    • The rest will do nothing with an excess.
Illustrative background for AmmoniaIllustrative background for Ammonia ?? "content

Ammonia

  • The four ions will all form precipitates with ammonia.
    • When you add excess ammonia to copper(II), it re-dissolves.
    • This is because you get the following ligand exchange:
    • [Cu(H2O)6]2+(aq) + NH3(aq) → [Cu(H2O)2(NH3)4]2+(aq)
  • The rest will do nothing on excess.
Illustrative background for Sodium carbonateIllustrative background for Sodium carbonate ?? "content

Sodium carbonate

  • Sodium carbonate will always generate a precipitate.
  • If the solution bubbles, you have an M(III) ion. If not, it’s an M(II) ion.
  • This can be used to distinguish between iron(II) and iron(III).

Colour Changes

In addition to the behaviours in each test tube reaction, you need to know the colours of everything produced.

Illustrative background for SolutionsIllustrative background for Solutions ?? "content

Solutions

  • These are the colours of the aqueous solutions of the above ions.
Illustrative background for HydroxidesIllustrative background for Hydroxides ?? "content

Hydroxides

  • These are the colours of the precipitates produced when hydroxide ions are added to the solutions.
Illustrative background for AmmoniaIllustrative background for Ammonia ?? "content

Ammonia

  • The only change on adding ammonia is that the copper ion goes a deeper blue.
Illustrative background for CarbonatesIllustrative background for Carbonates ?? "content

Carbonates

  • Upon adding sodium carbonate, the copper precipitates as a green-blue carbonate.

Jump to other topics

1Physical Chemistry

1.1Atomic Structure

1.1.1Fundamental Particles

1.1.2Isotopes & Mass Number

1.1.3Mass Spectrometry

1.1.4Electron Shells, Sub-Shells & Orbitals

1.1.5Electron Configuration

1.1.6Ionisation Energy

1.1.7Factors Affecting Ionisation Energies

1.1.8Trends of Ionisation

1.1.9Specific Impacts on Ionisation Energies

1.1.10End of Topic Test - Atomic Structure

1.1.11A-A* (AO3/4) - Atomic Structure

1.2Amount of Substance

1.2.1Relative Masses

1.2.2The Mole

1.2.3The Ideal Gas Equation

1.2.4Empirical & Molecular Formulae

1.2.5Balanced Equations

1.2.6Percentage Yield

1.2.7A-A* (AO3/4) - Percentage Yield

1.2.8Atom Economy

1.2.9End of Topic Test - Amount of Substance

1.2.10A-A* (AO3/4) - Substances & Yield

1.3Bonding

1.3.1Ionic Bonding

1.3.2Covalent & Dative Bonding

1.3.3Carbon Structures

1.3.4Metallic Bonding

1.3.5Physical Properties

1.3.6Shapes of Molecules

1.3.7Polarity

1.3.8Intermolecular Forces

1.3.9Intermolecular Forces 2

1.3.10End of Topic Test - Bonding

1.3.11Exam-Style Question - Shape of Molecules

1.3.12A-A* (AO3/4) - Bonding

1.4Energetics

1.4.1Enthalpy Changes

1.4.2Calorimetry

1.4.3Hess' Law

1.4.4Bond Enthalpies

1.4.5End of Topic Test - Energetics

1.5Kinetics

1.5.1Collision Theory

1.5.2Maxwell-Boltzmann Distribution

1.5.3Increasing Rates

1.5.4End of Topic Test - Kinetics

1.6Equilibria

1.6.1Le Chatelier

1.6.2Equilibrium Constants

1.6.3A-A* (AO3/4) - Energetics, Kinetics, Equilibria

1.6.4End of Topic Test - Equilibria

1.7Redox

1.7.1Redox

1.7.2End of Topic Test - Redox

2Physical Chemistry 2 (A2 Only)

2.1Thermodynamics (A2 Only)

2.1.1Born-Haber Cycles (A2 Only)

2.1.2Born-Haber Cycle Calculations (A2 Only)

2.1.3Entropy (A2 Only)

2.1.4Free Energy (A2 Only)

2.1.5End of Topic Test - Thermodynamics

2.1.6A-A* (AO3/4) - Thermodynamics

2.2Rate Equations (A2 Only)

2.2.1Rate Equations (A2 Only)

2.2.2Rate Equations 2 (A2 Only)

2.2.3The Arrhenius Equation (A2 Only)

2.2.4Experimental Methods for Rates (A2 Only)

2.2.5End of Topic Test - Rate Equations

2.2.6Exam-Style Question - Rates

2.2.7A-A* (AO3/4) - Rate Equations

2.3The Equilibrium Constant Kp (A2 Only)

2.3.1Properties of Kp (A2 Only)

2.4Electrochemical Cells (A2 Only)

2.4.1Electrochemical Cells (A2 Only)

2.4.2Electrochemical Series (A2 Only)

2.4.3Commercial Application (A2 Only)

2.4.4End of Topic Test - Kp & Electrochemistry

2.4.5A-A* (AO3/4) - Electrochemical Cells

2.5Acids & Bases (A2 Only)

2.5.1Brønsted-Lowry Acids & Bases (A2 Only)

2.5.2pH (A2 Only)

2.5.3The Ionic Product of Water (A2 Only)

2.5.4Weak Acids & Bases (A2 Only)

2.5.5pH Curves & Titrations (A2 Only)

2.5.6pH Curves & Titrations 2 (A2 Only)

2.5.7Buffer Solutions (A2 Only)

2.5.8End of Topic Test - Acids & Bases

2.5.9Exam-Style Question - Weak Acids

2.5.10A-A* (AO3/4) - Acids & Bases

3Inorganic Chemistry

3.1Periodicity & Trends

3.1.1The Periodic Table

3.1.2Trends in the Periodic Table

3.1.3End of Topic Test - Periodicity & Trends

3.2Group 2

3.2.1Group 2 Chemistry

3.2.2End of Topic Test - Group 2

3.3Group 7

3.3.1Introduction to Halogens

3.3.2Reactions of Halogens

3.3.3Chlorine & Chlorate(I)

3.3.4End of Topic Test - Group 7

3.3.5Exam-Style Question - Group 7

3.3.6A-A* (AO3/4) - Periodicity, Group 2 & 7

4Inorganic Chemistry 2 (A2 Only)

4.1Period 3 (A2 Only)

4.1.1Period 3 Elements & Oxides (A2 Only)

4.1.2Period 3 Oxides (A2 Only)

4.1.3End of Topic Test - Period 3

4.2Transition Metals (A2 Only)

4.2.1General Properties (A2 Only)

4.2.2Substitution Reactions (A2 Only)

4.2.3Shapes of Complex Ions (A2 Only)

4.2.4Colours of Ions (A2 Only)

4.2.5Variable Oxidation States (A2 Only)

4.2.6Titrations (A2 Only)

4.2.7Homogeneous Catalysts (A2 Only)

4.2.8Heterogeneous Catalysts (A2 Only)

4.2.9End of Topic Test - Transition Metals

4.2.10A-A* (AO3/4) - Transition Metals

4.3Reactions of Ions in Aqueous Solutions (A2 Only)

4.3.1Acidity (A2 Only)

4.3.2Identification (A2 Only)

4.3.3End of Topic Test - Reactions of Ions in Solution

5Organic Chemistry 1

5.1Introduction

5.1.1Naming Conventions

5.1.2Mechanism

5.1.3Isomerism

5.1.4End of Topic Test - Introduction to Organic Chem

5.2Alkanes

5.2.1Fractional Distillation

5.2.2Cracking

5.2.3Combustion

5.2.4Chlorination

5.2.5End of Topic Test - Alkanes

5.3Halogenoalkanes

5.3.1Substitution Reactions

5.3.2Elimination Reactions

5.3.3Ozone Depletion

5.3.4End of Topic Test - Halogenoalkanes

5.4Alkenes

5.4.1Introduction to Alkenes

5.4.2Reactions of Alkenes

5.4.3Polymerisation Reactions

5.4.4Properties of Polymers

5.4.5End of Topic Test - Alkenes

5.5Alcohols

5.5.1Production of Alcohols

5.5.2Oxidation of Alcohols

5.5.3Oxidation of Alcohols - 2

5.5.4Elimination Reactions

5.5.5End of Topic Test - Alcohols

5.5.6Exam-Style Question - Alcohols

5.6Organic Analysis

5.6.1Reactions

5.6.2Reactions 2

5.6.3Mass Spectrometry

5.6.4Infrared Spectroscopy

5.6.5End of Topic Test - Organic Analysis

5.7A-A* (AO3/4) - Organic 1

5.7.1A-A* (AO3/4) - Organic 1

6Organic Chemistry 2 (A2 Only)

6.1Optical Isomerism (A2 Only)

6.1.1Optical Isomerism (A2 Only)

6.1.2End of Topic Test - Optical Isomerism

6.2Aldehydes & Ketones (A2 Only)

6.2.1Aldehydes & Ketones (A2 Only)

6.2.2End of Topic Test - Aldehydes & Ketones

6.3Carboxylic Acids & Esters (A2 Only)

6.3.1Acids & Esters (A2 Only)

6.3.2Acylation (A2 Only)

6.3.3End of Topic Test - Carboxylic Acids & Esters

6.4Aromatic Chemistry (A2 Only)

6.4.1Structure & Reactivity (A2 Only)

6.4.2Reactions of Benzene (A2 Only)

6.4.3End of Topic Test - Aromatic Chemistry

6.5Amines (A2 Only)

6.5.1Nature & Preparation of Amines (A2 Only)

6.5.2Basicity & Nucleophilicity (A2 Only)

6.5.3End of Topic Test - Amines

6.6Polymers (A2 Only)

6.6.1Condensation Polymers (A2 Only)

6.6.2Biodegradability (A2 Only)

6.7Biological Organic (A2 Only)

6.7.1Amino Acids (A2 Only)

6.7.2Proteins (A2 Only)

6.7.3DNA (A2 Only)

6.7.4Anti-Cancer Drugs (A2 Only)

6.7.5End of Topic Test - Biological Organic

6.8Organic Synthesis (A2 Only)

6.8.1Organic Synthesis (A2 Only)

6.8.2Examples of Synthetic Routes (A2 Only)

6.8.3End of Topic Test - Polymers & Organic Synthesis

6.9NMR Spectroscopy (A2 Only)

6.9.1Understanding NMR (A2 Only)

6.9.2Carbon-13 NMR (A2 Only)

6.9.3Hydrogen-1 NMR (A2 Only)

6.9.4Hydrogen-1 NMR 2 (A2 Only)

6.9.5End of Topic Test - NMR

6.10Chromatography (A2 Only)

6.10.1Overview of Chromatography (A2 Only)

6.10.2Thin-Layer Chromatography (A2 Only)

6.10.3Column Chromatography (A2 Only)

6.10.4Gas Chromatography (A2 Only)

6.10.5End of Topic Test - Chromatography

6.11A-A* (AO3/4) - Organic 2

6.11.1A-A* (AO3/4) - Organic 2

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Acidity (A2 Only)

End of Topic Test - Reactions of Ions in Solution