Question

A substance which gives brick red flame and breaks down on heating to oxygen and a brown gas is:
(a)- Magnesium nitrate
(b)- Calcium nitrate
(c)- Barium nitrate
(d)- Strontium nitrate

Answer 1

Hint: The compounds of s-block i.e., alkali metals and alkaline earth metal salts impart characteristics color to the flame. Brick red color is imparted by the element which has atomic number 20.

Complete step by step answer:
The elements of alkali metal compounds and alkaline earth metal compounds impart characteristic color to the flame.
From alkaline earth metals calcium when put into a flame gives a brick red color, strontium gives Crimson red color, Barium gives apple green color, and Radium gives crimson color.
This can be explained, when alkaline earth metals or their compounds are put into a flame, the electrons absorb energy and are excited to higher levels. When they return to their ground state
(normal state), the absorbed energy is emitted in the form of visible light of a particular wavelength.
So, from the above, we can see that the compound of calcium gives a brick red color flame. So, it could be a calcium nitrate.
Calcium nitrate when heated gives calcium oxide, oxygen, and $N{{O}_{2}}$.

$2Ca{{(N{{O}_{3}})}_{2}}\to 2CaO+{{O}_{2}}+4N{{O}_{2}}\uparrow (brown\,gas)$
So, the correct answer is “Option B”.

Note: Beryllium and magnesium atoms are smaller in size and their electrons are strongly held by the nucleus. They need a large amount of energy for excitation of electrons to higher energy which is not available in the Bunsen burner flame. So, they do not impart color to the flame.