A compound that gives a brick-red colour to a non-luminous flame is likely to contain

Analysis

The question asks for the identification of a metal ion based on the characteristic color it imparts to a non-luminous Bunsen flame. This is a classic Flame Test question in inorganic chemistry.

Concept: Flame Test

The flame test is an analytical procedure used in chemistry to detect the presence of certain metal ions based on the characteristic emission spectrum produced by each element when heated in a flame. When an element is heated, its electrons absorb energy and jump to higher energy levels. As they return to their ground state, they emit light at specific wavelengths, which we perceive as distinct colors.

Here are the common flame test colors for the ions listed:

• Copper ions ($Cu^{2+}$): Produce a blue-green flame.
• Sodium ions ($Na^+$): Produce an intense golden-yellow flame.
• Calcium ions ($Ca^{2+}$): Produce a brick-red (or orange-red) flame.
• Potassium ions ($K^+$): Produce a lilac (or pale violet) flame.

Step-by-Step Solution

1. Identify the requirement: We are looking for the ion that produces a "brick-red" flame.
2. Evaluate the options: • Option A (Copper) is incorrect because it gives a green flame. • Option B (Sodium) is incorrect because it gives a yellow flame. • Option C (Calcium) matches the description of a brick-red flame. • Option D (Potassium) is incorrect because it gives a lilac flame.
3. Conclusion: Based on standard flame test observations, calcium compounds are the ones responsible for the brick-red coloration.

Exam Tip

To remember these colors easily, use a mnemonic:

• Sodium = Sun (Yellow)
• Calcium = Carrot (Brick-red/Orange)
• Potassium = Purple/Lilac
• Copper = Color of the sea (Blue-green)