Question

Elements of group 1 give colour in Bunsen Burner due to:
1. Low ionisation potential
2. Low melting point
3. Softness
4. One electron in outermost orbit

Answer 1

Correct Answer - Option 1 : Low ionisation potential

Concept:

• Alkali metals lie on the extreme left of the periodic table in Group 1.
• They have low ionization potential as they have loosely bound electrons.
• Alkali metals are extremely soft and can be cut with a knife.
• Alkali metals are highly reactive and some of them react violently in water.
• Sodium metal is stored in kerosene and potassium and lithium are stored wrapped in Paraffin wax.
• Most of them are ionic in nature.

Explanation:

• Flame test:
  • Alkali metals solution when placed in the oxidizing flame of the burner gives a characteristic colored flame.
  • Alkali metals have low ionization enthalpy and the heat supplied provides them with sufficient energy which makes the outermost electron transition to higher energy levels.
  • As higher energy levels are not stable, the electron in excited states falls back to ground levels, which emits radiation of characteristic color.
  • Thus each ion gives a unique color.
  • Li gives a Magenta color flame, Na gives a golden-yellow flame, Potassium gives a lilac flame and Cesium gives purple flame.
  • The flames are used to detect the presence of Metals in a salt sample.
  • Metals with high ionization potential do not respond to this test.

Hence, the color given by alkali metals in Bunsen Burner is due to their Low Ionisation potential.

• Other metals that give these tests are Calcium, Barium, Strontium, etc.
• Each flame has a unique color and is used to identify the presence of the metals.