When solid lead(II) trioxonitrate(V), Pb(NO_3)_2, is heated strongly in a dry test tube, i… — JAMB UTME

When solid lead(II) trioxonitrate(V), $Pb(NO_3)_2$ , is heated strongly in a dry test tube, it decomposes to yield a yellow solid residue, oxygen gas, and a reddish-brown gas. Which formula represents this reddish-brown gas, and what is the oxidation state of nitrogen in it?

$NO_2$ with an oxidation state of $+4$ Answer
B
$N_2O$ with an oxidation state of $+1$
C
$NO$ with an oxidation state of $+2$
D
$N_2O_5$ with an oxidation state of $+5$

Answer

The reddish-brown gas is nitrogen(IV) oxide (

NO_2

), in which nitrogen has an oxidation state of

+4

Heating lead(II) trioxonitrate(V) decomposes it into lead(II) oxide (

PbO

), nitrogen(IV) oxide (

NO_2

), and oxygen (

O_2

). Nitrogen(IV) oxide is a characteristic reddish-brown gas, and assigned oxidation state calculations give

+4

for nitrogen in

NO_2

Step-by-Step Solution

Write the balanced chemical equation for the thermal decomposition of lead(II) trioxonitrate(V).

2Pb(NO_3)_2(s) \rightarrow 2PbO(s) + 4NO_2(g) + O_2(g)

Heavy metal nitrates decompose on heating to yield the metal oxide, nitrogen(IV) oxide gas, and oxygen gas.

Identify the physical property of the gaseous products.

PbO

is a yellow solid residue (when hot/cold depending on form),

O_2

is a colorless gas, and

NO_2

is a distinctive reddish-brown acidic gas.

Nitrogen(IV) oxide (

NO_2

) is the only brown oxide of nitrogen produced in this reaction.

Calculate the oxidation state of nitrogen in

NO_2

Let

x

be the oxidation state of N.

x + 2(-2) = 0 \implies x = +4

Oxygen has an oxidation number of

-2

in neutral covalent oxides.

Key Concept

Thermal Decomposition of Metal Nitrates and Oxides of Nitrogen

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