Flame Tests for Cations

Flame Tests

Purpose of Flame Tests

  • Method used to test for positive ions (cations) in a compound through observation of color changes in a flame.

Procedure for Flame Tests

  1. Preparation of Nichrome Wire

    • Dip the nichrome wire into concentrated hydrochloric acid.

  2. Sample Preparation

    • Dip the treated nichrome wire into the sample being tested.

  3. Flame Observation

    • Place the loop of wire into a blue Bunsen flame and observe the color produced.

Color Observations of Common Cations

  • The following colors are associated with specific cations:

    • Crimson: Lithium (Li⁺)

    • Yellow-Orange: Sodium (Na⁺)

    • Lilac: Potassium (K⁺)

    • Red: Rubidium (Rb⁺)

    • Blue: Caesium (Cs⁺)

    • Dark Red: Calcium (Ca²⁺)

    • Crimson: Strontium (Sr²⁺)

    • Green: Barium (Ba²⁺)

Explanation of Color Production

  • Electron Behavior

    • Electrons in the shells of the atoms move to higher energy levels when they absorb energy from the flame.

    • As electrons drop back down to lower energy levels, they release light.

  • Color Formation

    • Different colors are emitted based on the difference in energy levels of the electrons, which determines the wavelength of light released.

Reference

  • For more detailed explanations regarding flame tests and electron transitions, see Topic 1 in the relevant material.