Tests for Ions

Tests for Ions

Cations - Positive Ions

• Flame tests can be used to identify some metal ions (cations).
• Lithium ions colour the flame crimson.
• Sodium ions colour the flame yellow.
• Potassium ions colour the flame lilac.
• Copper ions colour the flame green.
• Calcium ions colour the flame brick-red.

Testing for Ammonium Ions (NH4+)

• Ammonium ions react with sodium hydroxide to produce ammonia gas.
• The ammonia gas can be detected by its characteristic smell or by turning damp red litmus paper blue.

Anions - Negative Ions

• Carbonate ions (CO3 2-) react with dilute acids to produce carbon dioxide gas.
• Sulfate ions (SO4 2-) form a white precipitate when reacted with barium chloride in the presence of dilute hydrochloric acid.
• Halides (Cl-, Br-, I-) form different coloured precipitates when reacted with silver nitrate in the presence of nitric acid: chloride gives a white precipitate, bromide a cream precipitate, and iodide a yellow precipitate.

Testing for Specific Ions

• The presence of hydrogen ions (H+) in a solution can be tested using a pH meter or universal indicator paper. Acids have a pH less than 7.
• The presence of hydroxide ions (OH-) in a solution can also be tested using a pH meter or universal indicator paper. Alkalis have a pH greater than 7.
• Carbon Dioxide (CO2) released in a reaction can be tested by bubbling the gas through lime water, which then turns a milky/cloudy colour.

Remember, safety is paramount while performing these tests. Always wear safety glasses and handle chemicals with care.