Question

An aqueous solution of metal nitrate P reacts with sodium bromide solution to form yellow ppt of compound Q which is used in photography. Q on exposure to sunlight undergoes decomposition reaction to form metal present in P with reddish brown gas. Identify P&Q. Write the chemical reaction and the type of chemical reaction.

Answer 1

An aqueous solution of Silver nitrate reacts with sodium bromide solution to form yellow ppt of compound
Silver bromide which is used in photography.
IT IS A DOUBLE DISPLACEMENT reaction where mutual exchange of ions takes between reactants.
BALANCED CHEMICAL EQUATION:
2Ag (NO3) (aq)+ 2 NaBr (aq) -----> 2AgBr (s) + NaNO3 (aq)
Element P = Silver Nitrate
Element Q = Silver Bromide which is used in photography.

Silver Bromide on exposed to sunlight decomposes to silver metal and brown Bromine gas.
It is Photo chemical decomposition reaction where compound split up into it's constituents by sunlight energy.
BALANCED CHEMICAL Equation:
2AgBr-----> 2Ag (s) + Br2 ( g).

Answer 2

The metal nitrate P is silver nitrate.

It could be any metal nitrate but only silver chloride and silver bromide are used for photography.

AgNO3 + NaBr ------> AgBr + NaNO3.

This is double displacement reaction.

The yellow precipitate is AgBr.

AgBr is the compound Q.

AgBr in sunlight decomposes to form silver {the metal present in compound P (silver nitrate.).} and reddish brown gas bromine.

2AgBr ------> 2Ag + Br2.

This photochemical decomposition reaction as light energy is absorbed for the reaction to take place.

So,

compound P is AgNO3 (silver nitrate.).

Compound Q is AgBr (silver bromide.).

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