Question

Potassium chromate solution is added to an aqueous solution of a metal chloride. The precipitates thus obtained are insoluble in acetic acid. These are subjected to flame tests. Then the colour of the flame is?
A. Lilac
B. Apple green
C. Crimson red
D. Golden yellow

Answer 1

Hint: Since it is provided that the precipitates obtained when Potassium Chromate ${K_2}Cr{O_4}$ solution is added to aqueous solution of a metal chloride is insoluble in acetic acid and then is subjected to flame test, $B{a^{2 + }}$ gives yellow precipitate with ${K_2}Cr{O_4}$ solution. So the colour of the flame will be the colour $B{a^{2 + }}$ gives in the flame test.

Complete step-by-step answer:
Potassium Chromate is a yellow, crystalline, inorganic compound that releases poisonous chromium fumes upon heating. Potassium chromate is very corrosive and is a good oxidizing agent. Potassium chromate is used in the manufacture of dyes and in textile industries.
A flame test is a scientific method used to identify the presence of certain elements, mainly metal ions, based on each element's characteristic emission spectrum. The colour of flames is also dependent on the temperature in general.

Whenever the atoms of a gas are excited, their electrons jump from their ground states to higher energy levels. This energy correlates to particular wavelengths of light, which produces particular colours of light.
According to the question: Potassium chromate solution is added to an aqueous solution of a metal chloride and forms a precipitate which is insoluble in Acetic acid ($C{H_3}COOH$)
${K_2}Cr{O_4}\, + \,MCl\, \to \,ppt$
Now this precipitate is insoluble in $C{H_3}COOH$
We know that $B{a^{2 + }}$ ions give a yellow precipitate on reaction with ${K_2}Cr{O_4}$ and also the resulting precipitate is not soluble in $C{H_3}COOH$. Thus the colour of the flame will be apple green.
Hence, option B is correct.

Note: It is always a good habit to memorise the colours given by the common metal ions. For instance Lithium ($L{i^ + }$ion) gives red flame colour, whereas Sodium ($N{a^ + }$ ion) gives yellow colour and Potassium (${K^ + }$ ion) gives lilac flame test colour.