Lesson Explainer: Properties of Nitrogen Chemistry

In this explainer, we will learn how to describe and explain the properties and reactions of the element nitrogen.

Nitrogen is arguably the most well-known group 15 element. It is slightly soluble in water, but its solubility does depend on the surrounding temperature and pressure. It is the most abundant gas in Earth’s atmosphere, and it is colorless, odorless, and unreactive. Nitrogen gas is chemically unreactive because there is a strong NN triple bond in each diatomic N2 gas molecule, as can be seen below. NN

As a neutral gas, nitrogen has no effect on litmus solutions. To overcome nitrogen’s unreactive nature, reactions involving nitrogen in its elemental form often require the presence of an electric spark, or strong heating to proceed, in order to break the triple covalent bond, which has a bond enthalpy of 942 kJ/mol.

Other important physical properties and information about nitrogen can be found in the following table:

Melting point of nitrogen210C
Boiling point of nitrogen196C
Density1.25 g/L
Common oxidation states3, 2, 1, +1, +2, +3, +4, +5

Example 1: Identifying the Physical and Chemical Properties of Nitrogen Gas

Which of the following is not a property of nitrogen gas?

  1. Its structure is two nitrogen atoms joined by a triple covalent bond.
  2. It is a colorless, odorless, tasteless gas.
  3. It has a neutral effect on litmus paper.
  4. It is heavier than air.
  5. It is slightly soluble in water.

Answer

In this question, we are asked to identify which of a list of properties is not accurate when describing nitrogen gas.

Answer A tells us that nitrogen’s structure is two nitrogen atoms joined by a triple covalent bond, and with three electrons in the p subshell of nitrogen atoms all involved in forming covalent bonds in the diatomic molecules of nitrogen, we know that answer A is a property of nitrogen gas and is therefore not the correct answer.

Nitrogen is used in packets of chips to provide an inert atmosphere and stop the oxidation of food before it is eaten because it is colorless, odorless, and tasteless. We can use these statements to determine that answer B must also be incorrect.

As an inert gas with no acidic or basic properties, we would expect nitrogen gas to have a neutral effect on litmus paper, meaning answer C is incorrect.

Air is primarily made up of nitrogen molecules (N2) and oxygen molecules (O2). Most oxygen molecules have a molecular mass of 32 and most nitrogen molecules have a molecular mass of 28. The average molecular mass of an air molecule must be between 28 and 32 and this is heavier than the mass of the average nitrogen molecule. This logic shows that nitrogen is lighter than air and it also suggests that answer D is the correct answer.

Nitrogen is slightly soluble in water although the amount that dissolves varies depending on other conditions, and so answer D is correct.

Air is a mixture, and isolating nitrogen from it is possible in the laboratory, providing we are able to remove the carbon dioxide, water, and oxygen found in a typical air mixture.

The apparatus is set up as shown in the diagram, and in the first instance, water is used to seal the first container.

The air bubbles through the caustic solution of sodium hydroxide found in the second container where a reaction occurs between sodium hydroxide and carbon dioxide, removing it from the air mixture: 2NaOH()+CO()NaCO()+HO()aqgaql2232

The remaining chemicals then pass through concentrated sulfuric acid in container three, which dehydrates the air mixture and removes the water vapor.

What remains of the air mixture then passes into a horizontal open-ended glass tube where the gases pass over a small pile of strongly heated copper turnings. Oxygen is removed from the gas mixture as it reacts with the heated copper turnings: 2Cu()+O()2CuO()sgs2

The remaining gas, which is almost pure nitrogen, is collected over mercury in a gas cylinder.

Example 2: The Use of Copper in the Preparation Process of Nitrogen from Atmospheric Air

In the preparation process of nitrogen from atmospheric air, what is the role of red-hot copper turnings?

Answer

In order to remove nitrogen from atmospheric air, it is necessary to remove the other unwanted gases in the air, namely, the oxygen, carbon dioxide, and water vapor.

Carbon dioxide can be neutralized and removed using a caustic solution as it is an acidic gas, so this is unlikely the role of red-hot copper turnings. The water vapor is most commonly removed using a dehydrating agent such as concentrated sulfuric acid.

Copper turnings when heated can act as a reducing agent and, in this instance, react with the oxygen gas to remove this gas from what remains of the air mixture. The correct answer is to remove oxygen gas.

Another method of preparing nitrogen in a laboratory involves the heating of a mixture of ammonium chloride and sodium nitrite solutions.

The apparatus is set up as shown in the diagram, and the ammonium chloride is added dropwise to a heated solution of sodium nitrite.

This has the effect of creating ammonium nitrite in situ, which can then decompose into water and nitrogen gas. The reaction is performed in this way as ammonium nitrite is highly unstable and cannot be prepared ahead of time. The overall equation for this reaction is NaNO()+NHCl()NaCl()+2HO()+N()2422aqaqaqlg

However, the decomposition in which we are interested only involves ammonium nitrite: 2NHNO()4HO()+N()4222aqlg

Having been isolated either from the air or through chemical reactions, elemental nitrogen is capable of a few noteworthy reactions. The first of these, which must be initiated using an electric spark, is the reaction with hydrogen to form ammonia gas: N()+3H()2NH()223gggCelectricspark

In a similar fashion, an electric arc can be used to initiate the reaction between nitrogen and oxygen gases to form nitric oxide, in a two-step process initially creating nitrogen monoxide: N()+O()2NO()22gggCelectricarc which reacts with more oxygen to form nitrogen dioxide: 2NO()+O()2NO()ggg22

Example 3: Identifying the Product from the Reaction between Nitrogen and Oxygen

The inert nature of nitrogen gas (N2) can be overcome by using powerful electric arcs to break the bonds between the two atoms. In an atmosphere of hydrogen and nitrogen, an electric arc causes ammonia gas (NH3) to be formed. What is the major product when an electric arc initiates a reaction in an atmosphere of nitrogen and excess oxygen?

  1. NO25
  2. NO
  3. NO23
  4. NO2
  5. NO2

Answer

In this reaction, an electric arc is required to break the strong bonds that exist between the atoms in a molecule of nitrogen gas. When these atoms react with oxygen molecules, they initially form unstable nitrogen monoxide (NO) molecules. The nitrogen monoxide molecules quickly react oxygen atoms and they form more stable nitrogen dioxide gas, so answer E the correct one.

Although nitrogen is unreactive at high temperatures, it will react with strong reducing metals such as magnesium to form magnesium nitride in the following direct combination reaction: 3Mg()+N()MgN()sgs232

This greenish-yellow powder decomposes when we mix it with water, and this reaction produces ammonia gas and magnesium hydroxide: MgN()+6HO()2NH()+3Mg(OH)()32232slgaq

Example 4: Identifying the Product from the Reaction between Nitrogen and Oxygen

Magnesium nitride reacts vigorously with water to form ammonia and magnesium hydroxide, according to the following reaction: MgN+HONH+Mg(OH)32232

Which of the following numbers, in the right order, are the stoichiometric coefficients missing from the reaction equation?

  1. 1, 3, 1, 2
  2. 1, 3, 2, 2
  3. 2, 6, 4, 3
  4. 2, 3, 4, 3
  5. 1, 6, 2, 3

Answer

Although this question essentially only involves the balancing of a chemical equation, it is not trivial because we have to deal with atoms that have a valence of three.

If we start with the magnesium nitride and assume that the correct stoichiometric value for that substance is one, then the magnesium hydroxide product must be three. This is reinforced by the fact that three of the answers also agree with this line of reasoning, so it appears we may be on the right track.

If the magnesium hydroxide has a stoichiometric value of three, then we must have six oxygen atoms in total in the products, meaning that we must have six oxygen atoms in the reactants, which means that the stoichiometric value for water should be six. This line of reasoning is reinforced in answers C and E.

Looking at either the total number of hydrogen atoms or the total number of nitrogen atoms, we can finally conclude that the stoichiometric value for ammonia must be two in order for this equation to be balanced, and this is in line with answer E, which is the correct answer.

An industrially important reaction of nitrogen involves the reaction with calcium carbide, again using an electric arc, in order to form a chemical known as calcium cyanamide, which is used as a fertilizer: N()+CaC()CaCN()+C()222gsssCelectricarc

While it may not be obvious at initial inspection why the product, calcium cyanamide, would be a particularly effective fertilizer, we can produce two much more familiar chemicals when we add water: CaCN()+3HO()2NH()+CaCO()2233slgs

This production of ammonia, when calcium cyanamide comes into contact with water, introduces ammonia into the soil, providing a source of nitrogen that is essential for plants and crops to grow effectively.

One of the most important nitrogen compounds is ammonia, which is made on an industrial scale using the Haber–Bosch process. Nitrogen and hydrogen gases react at around 500C using a transition metal catalyst. This reaction is usually carried out in a pressurized vessel at around 200 atm, with much of the ammonia produced being used in the production of fertilizers.

Reaction: Formation of Ammonia in the Haber–Bosch Process

N()+3H()2NH()223gggFe/MocatalystC,atm

It is, however, possible to produce ammonia gas in the laboratory using a mixture of ammonium chloride and calcium hydroxide: 2NHCl()+Ca(OH)()CaCl()+2HO()+2NH()42223ssslg

Having attempted this experiment in a laboratory, if it were the case that you wanted to test whether or not you had correctly produced ammonia gas, one of the easiest tests you can do is to use hydrogen chloride vapor. HCl()g can be generated from concentrated hydrochloric acid to react with ammonia and form ammonium chloride: NH()+HCl()NHCl()34ggs

Ammonium chloride is a white crystalline solid that initially forms as a vapor; this can be seen in the picture below.

Chemical experiment - misty ammonium chloride

Key Points

  • Nitrogen can be produced both in the laboratory and on an industrial scale.
  • Nitrogen is a colorless, odorless, and unreactive gas.
  • Nitrogen is unreactive due to its triple covalent bond between the nitrogen atoms in the diatomic molecules.
  • Nitrogen reacts with hydrogen, oxygen, magnesium, and calcium carbide.
  • Ammonia is a common nitrogen compound that can be produced industrially by the Haber–Bosch process and in a laboratory.
  • Ammonia is an essential chemical to society because of its use as a precursor to many fertilizers.

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