Which of the following compounds will burn with a brick-red colour in a non-luminous Bunsen flame?

Analysis

The question asks for the identification of a specific metal salt based on the characteristic flame colour it produces when heated in a non-luminous Bunsen flame. This is a classic test in qualitative analysis known as the Flame Test.

Concept: Flame Test

The flame test is used to detect the presence of certain metallic ions. When these metal salts are heated, the electrons in the metal atoms absorb energy and move to higher energy levels. As they return to their ground state, they emit light at specific wavelengths, which appear as distinct colours to the human eye.

Here are the characteristic flame colours for the metals in your options:

• Lithium (Li⁺): Produces a crimson (deep red) flame.
• Sodium (Na⁺): Produces a golden-yellow flame.
• Calcium (Ca²⁺): Produces a brick-red flame.
• Magnesium (Mg²⁺): Does not produce a characteristic flame colour (it is often considered non-flame-active in standard school laboratory tests).

Step-by-Step Solution

1. Examine the options: We are looking for the compound that contains the metal ion responsible for a "brick-red" flame.
2. Evaluate the metals: • LiCl contains Lithium (Crimson). • NaCl contains Sodium (Golden-yellow). • CaCl₂ contains Calcium (Brick-red). • MgCl₂ contains Magnesium (No characteristic colour).
3. Match the observation: Since Calcium ions (Ca²⁺) are known to impart a brick-red colour to a non-luminous flame, the compound CaCl₂ is the correct choice.

Conclusion

Exam Tip

To remember these easily for your JAMB or WASSCE exams, use this mnemonic:

• Sodium = Sunny yellow
• Calcium = Chili red (Brick-red)
• Potassium = Purple (Lilac)
• Lithium = Lovely crimson