CAIE A-Level Chemistry 12.1 Nitrogen, Ammonia and NOx

Practise explaining nitrogen inertness, ammonia acid–base chemistry and the atmospheric reactions of nitrogen oxides.

Exam points

explain nitrogen’s low reactivity using its strong non-polar N≡N triple bond
use proton transfer to explain ammonia basicity, ammonium formation and ammonia displacement
connect NO and NO2 separately to catalytic converters, PAN formation and acid-rain chemistry

Covered syllabus points

12.1.1—Lack of reactivity of nitrogen, using triple 12.1.2—And explain 12.1.3—NOx sources and catalytic removal 12.1.4—Atmospheric NOx and photochemical smog 12.1.5—Role of NO and NO2 in the formation of acid

[Maximum number: 1]

Compounds P, Q and R have all been found in the atmosphere of one of Saturn's moons.
P

Figure for Question 12.1 Nitrogen and sulfur question 1 — CAIE A-Level Chemistry AS

The equation for the complete combustion of $\mathbf{P}, \mathrm{C}_{4} \mathrm{~N}_{2}(\mathrm{I})$ , is shown.

\mathrm{C}_{4} \mathrm{~N}_{2}(\mathrm{I})+4 \mathrm{O}_{2}(\mathrm{~g}) \rightarrow 4 \mathrm{CO}_{2}(\mathrm{~g})+\mathrm{N}_{2}(\mathrm{~g}) \quad \Delta H=-2036 \mathrm{~kJ} \mathrm{~mol}^{-1}

One of the products of the complete combustion of P is nitrogen gas, $\mathrm{N}_{2}(\mathrm{~g})$ .

Explain the lack of reactivity of nitrogen.

[Maximum number: 5]

Nitrogen and phosphorus are elements in Group 15 of the Periodic Table.

(a)

Nitrogen is found in inorganic compounds such as nitrogen oxides ( $\mathrm{NO}_{x}$ ), nitrates and nitric acid.

[ 4 ]

(i)

Identify one natural and one man-made occurrence of nitrogen oxides in the atmosphere.
natural
man-made

[ 2 ]

(ii)

Write an equation to describe the role of $\mathrm{NO}_{2}$ in the direct formation of acid rain.

[ 1 ]

$2 \mathrm{NO}_{2}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{HNO}_{2}+\mathrm{HNO}_{3} \mathrm{OR} 4 \mathrm{NO}_{2}+\mathrm{O}_{2}+2 \mathrm{H}_{2} \mathrm{O} \rightarrow 4 \mathrm{HNO}_{3}$

(iii)

Peroxyacetyl nitrate, PAN, is a component of photochemical smog.

Describe how PAN forms from $\mathrm{NO}_{2}$ .

3 Nitrogen and phosphorus are elements in Group 15 of the Periodic Table.
(v) Describe what is seen when solid calcium nitrate is heated strongly.
(b) A common test for nitrates is the reaction with NaOH and Al . Equation 1 shows the reaction.

[ 1 ]

It / $\ce{NO2}$ reacts with (unburned) hydrocarbons / $\ce{VOCs}$

ALLOW reaction of unburned hydrocarbons / $\ce{VOCs}$ in presence of $\ce{NO2}$

(b)

A common test for nitrates is the reaction with NaOH and Al . Equation 1 shows the reaction.

\text { equation } 1 \quad 3 \mathrm{NO}_{3}^{-}+8 \mathrm{Al}+5 \mathrm{OH}^{-}+18 \mathrm{H}_{2} \mathrm{O} \rightarrow 3 \mathrm{NH}_{3}+8\left[\mathrm{Al}(\mathrm{OH})_{4}\right]^{-}

[ 1 ]

(i)

$\mathrm{NH}_{3}$ is a basic gas.

Describe how $\mathrm{NH}_{3}$ is able to act as a base.

[ 1 ]

( $\mathrm{NH}_{3}$ is an) $\mathrm{H}^{+}$ acceptor

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Covered syllabus points

12.1 Nitrogen and sulfur question 1

12.1 Nitrogen and sulfur question 2

Question (a)

Question (i)

Question (ii)

Question (iii)

Question (b)

Question (i)