Why ionic compounds form colourless flames?

Asked by Pragnya Kar | 30th Jun, 2014, 11:42: PM

Expert Answer:

Ionic compounds can form coloured flames.

Solutions of ions, when mixed with concentrated HCl and heated on a nickel/chromium wire in a flame, cause the flame to change to a color characteristic of the atom. Visible colors occur with the following ions:

Sodium

Bright yellow (intense, peristent)

Potassium

Pale violet (slight, fleeting)

Calcium

Brick red (medium, fleeting)

Strontium

Crimson (medium)

Barium

Light green (slight)

Lead

Pale bluish (slight, fleeting)

Copper

Green or blue (medium, persistent)

A flame test can be used to distinguish between Na+ and K+. Na+ makes a yellow flame while K+ turns the flame a lilac/violet colour. However, flame tests are not required for this standard.

Answered by Hanisha Vyas | 1st Jul, 2014, 11:58: AM