Question

A powdered salt (X) in a dry test tube was heated that evolves brown fumes of nitrogen dioxide and a yellow residue of lead oxide is also formed. The salt (X) is
A. MgCO3
B. Pb(NO3)2
C. (NH4)2SO4
D. CaCO3

Answer 1

$\huge\star{\green{\underline{\mathfrak{Answer :-}}}}$

B) $\sf{Pb(NO_3)_2}$

This compound is also called lead nitrate.

$\rule{200}2$

Lead nitrate is a powdered salt which is given as X in the question. When dry lead nitrate is heated in a test tube, a brown fumes of nitrogen dioxide evolves. And at last yellow residue of lead is left in the test tube.

$\rule{200}2$

The chemical reaction involved in this process is:

$\tt{2Pb(NO_3)_2\longrightarrow(Heat) 2PbO +4NO_2+O_2}$

$\rule{200}4$

Answer 2

$\Huge{\underline{\boxed{\bf{SOLUTION}}}}$

The powdered salt (X) is $\huge{\red{Lead\:Nitrate}}$

OPTION (B) is correct here → Pb(NO3)2

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Now, let us know what exactly happened →

•Chemical reaction involved here -

2Pb(NO3)2→ 2PbO + 4NO2 + O2

•Explaination -

The above reaction is example of thermal decomposition.

When powdered salt is heated it decomposes to release the gas which is nitrogen dioxide and the yellow residue left behind is lead oxide which clearly indicates that salt is LEAD SALT.

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