Flame & precipitate tests

Session focus: Identifying cations and anions using colour results from flame and precipitate tests

Today, the students were taught how to perform a flame test - an analytical technique used to identify the presence of certain metal ions in a sample based on the distinct colors they produce when heated in a flame. They carried out the flame test on five different metal salts containing the following ions: Lithium, Sodium, Potassium, Copper and Zinc. Through this practical, they also learned the importance of avoiding contamination between the salts as to obtain accurate results.

The second portion of the lab was based around the precipitate tests, a process used to identify the presence of specific ions in a solution based on the colour of the insoluble compounds formed. They learned to distinguish between the Iron (II), Iron (III) and Copper (II) ions.

Lesson materials:

Chemicals:

Metal salts ofLithium, Sodium, Potassium, Copper, Zinc

Dilute Hydrochloric Acid

Iron (II) Sulfate

Iron (III) Chloride

Copper (II) Sulfate

Sodium Hydroxide

Sodium Sulfate

Barium Chloride

Equipment:

Bunsen burners

Boiling tubes

Pipettes

Beakers

Platinum Wire

Test tube rack

Lesson plan:

• Introductory slides

• Ask students to create a table

Part 1 - Flame tests

•  Lithium, Sodium, Copper, Potassium, Zinc

Part 2 - Precipitate tests

• Iron II Sulfate + NaOH (green)

• Iron III Chloride + NaOH (brown)

• Copper II Sulfate + NaOH (blue)

• Sodium Sulfate + BaCl2 (white