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HSC Chemistry

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  1. Module 5: Equilibrium and Acid Reactions
    5.1 Static and Dynamic Equilibrium
    5 Topics
  2. 5.2 Factors that Affect Equilibrium
    2 Topics
  3. 5.3 Calculating the Equilibrium Constant
    2 Topics
  4. 5.4 Solution Equilibria
  5. Module 6: Acid/Base Reactions
    6.1 Properties of Acids and Bases
    7 Topics
  6. 6.2 Using Brønsted–Lowry Theory
    2 Topics
  7. 6.3 Quantitative Analysis
    1 Topic
  8. Module 7: Organic Chemistry
    7.1 Nomenclature
    2 Topics
  9. 7.2 Hydrocarbons
    2 Topics
  10. 7.3 Products of Reactions Involving Hydrocarbons
  11. 7.4 Alcohols
    1 Topic
  12. 7.5 Reactions of Organic Acids and Bases
  13. 7.6 Polymers
    2 Topics
  14. Module 8: Applying Chemical Ideas
    8.1 Analysis of Inorganic Substances
    3 Topics
  15. 8.2 Analysis of Organic Substances
  16. 8.3 Chemical Synthesis and Design
  17. Working Scientifically
    Working Scientifically Overview
    1 Topic

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Lesson 14, Topic 2
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Testing for Ions

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Cation analysis

Qualitative tests can be performed to identify the presence of various cations in solution.

Mg2+, Ca2+, and Ba2+ can be distinguished using several tests. Sulfuric acid produces white precipitates with Ca2+ and Ba2+. Sodium hydroxide produces only a white precipitate with Mg2+. Calcium ions produce an orange-red flame colour and barium ions produce a yellow-green flame colour.

Pb2+ and Ag+ both form white precipitates with HCl. However, PbCl2 is soluble in hot water.

Cu2+ ions form a blue precipitate with NaOH solution. Fe2+ ions form a green precipitate and Fe3+ ions form a brown precipitate with NaOH solution.

Flame tests

When aqueous solutions of various metal ions are atomised in a blue (non-luminous) Bunsen burner flame, they produce a characteristic colour in the flame. There are various methods to practically conduct a flame test.

Flame colour examples: Ba2+ = pale yellow-green, Cu2+ = green, Ca2+ = orange-red.

Anion Analysis

Various acid-base and precipitation reactions can be used to identify various anions.

CO32- and OH ions form alkaline solutions, which can be detected using a pH meter. Nitric acid causes effervescence of CO2 from CO32- ions but not with OH- ions.

Cl forms a white precipitate with Ag+, whereas Br forms a cream precipitate and I- forms a pale-yellow precipitate. AgCl dissolves in dilute ammonia. AgBr dissolves in concentrated ammonia solution. AgI does not dissolve in concentrated ammonia solution.

SO42- precipitates in an acidified solution of Ba2+, but PO43- will not. The phosphate ion will precipitate with barium ions in a solution made alkaline with ammonia solution. Acetate (CH3COO) ions do not precipitate with Ba2+ in acidic or alkaline solutions.