Further Analysis + Quantitative Chemistry

A cation is the positive ion. An anion is the negative ion.

Testing for cations

Flame Test:

• 1) Take a small sample from the container.
• 2) Clean the nichrome wire loop with hydrochloric acid.
• 3) Hold the loop in the blue flame of a bunsen burner. Repeat multiple times.
• 4) Use the colour of the flame to identify the metal element in the compound.

• Lithium - Bright Red flame
• Sodium -  Golden Yellow flame
• Potassium - Lilac flame
• Calcium - Brick red flame
• Barium - Green flame

Testing for precipitates using sodium hydroxide

Precipitate = insoluble salt

• 1) Add small sample of sodium hydroxide to metal salt in test tube.
• 2) Precipitate formed, can tell what it is by the colour.

• Al³+ - White Precipitate - Keep Adding NaOH, it'll redissolve.
• Ca²+ - White Precipitate - Flame Test produces brick red.
• Mg²+ - White Precipitate - Flame Test produces brick red.
• Cu²+ - Light Blue Precipitate.
• Fe²+ - Dirty Green Precipitate.
• Fe³+ - Brown Precipitate.

Testing for ammonium

Sodium hydroxide solution can also be used to test if ammonium ions are present. Ammonium reacts with NaOH to form ammonia and water.

If the solution is gently warmed, ammonia is driven off as a gas. We can detect this with damp red litmus paper. The litmus will turn blue as ammonia is an alkaline.

Testing for anions

To check for a carbonate, add hydrochloric acid and the result will be a fizz, meaning that carbon dioxide has been produced.

To check for a sulfate add hydrochloric acid followed by barium chloride solution. The white precipitate formed is the insoluble salt, barium sulfate.

To check for halide ions, add dilute nitric acid…