Question

A white salt on heating decomposes to give brown fumes

Answer 1

$\Large\underline\mathfrak{Question}$

A white salt on heating decomposes to give brown fumes

We should know to

a) Identify the salt and write it's chemical name.
b) Identify the name of the gas evolved.
c) Identify the type of chemical reaction.
d) write a balanced chemical equation for the reaction.

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a) Identification of salt and it's chemical name,

→ White salt producing the brown colour gas.
This indicates the presence of nitrate ion.

→ it may be the salt contains nitrate ion (NO3)-

for example ,

→ it must be lead nitrate " Pb (NO3)2 " if it implies the yellow colourish residue left after heating.

→ Chemical name of salt is

Pb (NO3)2 / or / X No3

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b) identification of gas evolved

→ The production of brown gas indicating that the nitrogen dioxide gas is evolved.

→ But , it may be the another gas

Example → in some chemical reactions bromine ( brown gas ) is produced .

→ The another one with the product must be oxygen ( included in this reaction ) which is colourless but can brightly glow ( Depends upon the quantity of oxygen ) .

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c) identification of reaction's type ,

→ As , we are supposing that this reaction involves the thermal heating / or / breakdown of the nitrate salt / lead nitrate which is given below ,

Pb(NO3)2 ––––––⟩ PbO + NO2 + O2

→ The Decomposition will take place if the temperature is in between 200 - 470 ( °C )

→ it involves thermal decomposition of Lead nitrate Pb(NO3)2.

→ So , it is Decomposition reaction.

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d) Balanced chemical equation for the decomposition of Lead nitrate ,

→ Balanced equation for this reaction is ,

2 Pb(NO3)2 ———— ⟩ 2 PbO + 4 NO2 + O2

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