Question

Calcium ions impart…..colour through blue glass.
A. green
B. pale green
C. violet
D. yellow

Answer 1

Hint:: As we know that every element specially alkali metal and alkaline earth metals has their own characteristic colour because these elements have one or two electrons in its outermost shell which can easily jump to excited state and emit colour with particular wavelength.

Complete answer:The colour of the alkaline earth metal ions depends upon the absorption of the frequency of light. The best method to detect the colour of the ions is flame test.
Flame test is used to detect the characteristic colour of the ions. As the name indicates, this method is completed by the colour of the flame in a particular temperature. As the temperature increases or decreases, the colour of the flame may also change.
When calcium ions undergo flame test, the colour of the flame turns brick red colour which means that the calcium ions have brick red colour characteristics.
When this brick red colour is seen by blue glass, it changes into pale green colour because now this blue glass acts as a prism which changes its wavelength and colour of the brick red reflects pale green to our eyes.

Therefore, Calcium ions impart pale green colour through blue glass.

Note:: Among the alkaline earth metals, beryllium and magnesium ions do not give any colour in the flame test. Strontium ions change flame into bright red colour. Barium ion gives green colour in the flame test. Alkaline earth metals impart colors because of low first ionization energy.