GCSE Nitrogen

Nitrogen

Nitrogen makes up 78% of the air and it is a highly unreactive gas. This is due to the fact that nitrogen has a triple bond, and the activation energy to break this bond is very high.

Nitrogen reacts with oxygen under extreme condition (thunderstorms, car engines) to form Nitrogen monoxide, which is then oxidised to nitrogen dioxide in the air.

Ammonia

Preparation

Industrial

The haber process is used to manufacture ammonia in industry.

Catalyst: Iron

Temperaeture: 400^oC (Even though the reaction is exothermic, a high temperature is used in order to increase the rate of reaction.

Pressure: 200 atm

Laboratory

Reacting Ammonium salts with alkali. This gives off the salt, water and ammonia.

$NH_4Cl + NaOH \rightarrow NaCl + H_2O + NH_3$

Properties

Basic

Ammonia has a lone pair on the nitrogen and therefore this can donate a pair of elecrtons making it a Lewis base. Ammonia can react with acids to produce ammonium salts while it can form bonds with B and Al since this both are electron deficient.

Solubility

Ammonia is very soluble in water to give a basic solution.

Reducing properties

Nitrogen has a number of different oxidation states, and ammonia is the lowest of these, meaning that it can be oxidised to higher oxidations states.

$2NH_3 + 3CuO \rightarrow N_2 + 3H_2O + 3Cu$

Ammonium salts

Most ammonium salts decompose to give ammonia and an acid, such as:

$NH_4Cl \rightarrow NH_3 + HCl$

Oxides of Nitrogen

Nitrogen monoxide NO

NO is quite unstable due to the fact that it has an odd number of electron and therefore it readily oxidises in air to form NO_2.

Nitrogen dioxide NO₂

It is a brown gas and can be prepared by the oxidation of copper with hot nitric acid.

$Cu + 4HNO_3 \rightarrow Cu(NO_3)_2 + 2NO_2 + 2H_2O$

It can also be prepared by the decomposition of nitrates are group II nitrates.

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

This can be collecting and purified by passing from a u-shaped tube over ice cold water. The NO₂ will dimerise to produce a liquid while the O₂ will remain gaseous.

When NO₂ dissolves in water it forms two different compounds:

$2NO2 + H2O \rightarrow HNO_3 + HNO_2$

Nitric acid HNO₃

Nitric (V) can be prepared from any nitrate salt reacting with an acid.

$NaNO_3+ HCl \rightarrow NaCl + HNO_3$

Nitric acid is a very good oxidising agent, and it has a number of reaction that it can undergo:

Hot copper

$Cu + 4HNO_3 \rightarrow Cu(NO_3)_2 + 2NO_2 + 2H_2O$

Nitrates

Nitrates are prepared with the reaction of nitric acid with a base.

Alkali nitrates break down to give nitrites while all other nitrates give nitrogen dioxide.