Introduction

Nitrogen is a vital element in the atmosphere, comprising about 78% of the air we breathe. It is a non-metal with the atomic number 7 and symbol N. Nitrogen forms various compounds, including ammonia, nitric acid, and nitrogen dioxide. Understanding the properties and reactions of nitrogen and its compounds is crucial in chemistry.

Nitrogen Gas

• Definition: Nitrogen gas ($N_2$) is a diatomic molecule consisting of two nitrogen atoms bonded together.
• Example: Calculate the mass of 2 moles of nitrogen gas.
  • Solution: The molar mass of nitrogen is 14.01 g/mol. Therefore, the mass of 2 moles of nitrogen gas is $2 \times 14.01 = 28.02$ g.

Ammonia

• Definition: Ammonia ($NH_3$) is a compound composed of one nitrogen atom bonded to three hydrogen atoms.
• Example: Write the balanced chemical equation for the synthesis of ammonia.
  • Solution: $N_2 + 3H_2 \rightarrow 2NH_3$

Nitric Acid

• Definition: Nitric acid ($HNO_3$) is a strong acid that is commonly used in the production of fertilizers and explosives.
• Example: Calculate the molarity of a solution containing 0.5 moles of nitric acid in 250 mL of solution.
  • Solution: Molarity is given by $M = \frac{\text{moles of solute}}{\text{volume of solution in liters}}$. Therefore, $M = \frac{0.5}{0.25} = 2$ mol/L.

Nitrogen Dioxide

• Definition: Nitrogen dioxide ($NO_2$) is a reddish-brown gas with a pungent odor, formed by the oxidation of nitrogen monoxide.
• Example: Determine the oxidation state of nitrogen in nitrogen dioxide.
  • Solution: In $NO_2$, oxygen has an oxidation state of -2. Since there are two oxygen atoms, the total oxidation state contributed by oxygen is -4. Therefore, nitrogen must have an oxidation state of +4 to balance the molecule.

Common Mistakes

• Forgetting Stoichiometry: Many students overlook the importance of stoichiometry in balancing chemical equations involving nitrogen compounds.
• Misinterpreting Oxidation States: Incorrectly determining oxidation states can lead to errors in predicting the reactivity of nitrogen compounds.

Key Points

• Nitrogen is a diatomic molecule that forms various compounds such as ammonia, nitric acid, and nitrogen dioxide.
• Understanding stoichiometry is crucial in balancing chemical equations involving nitrogen compounds.
• Correctly determining oxidation states helps in predicting the reactivity of nitrogen compounds.

Practice Questions

1. Write the chemical formula for nitric oxide.
   • Answer: $NO$
2. Calculate the percentage composition of nitrogen in ammonia ($NH_3$).
   • Answer: The molar mass of $NH_3$ is 17.03 g/mol. The mass of nitrogen in $NH_3$ is 14.01 g/mol. Therefore, the percentage composition of nitrogen is $\frac{14.01}{17.03} \times 100%$.
3. Balance the chemical equation for the reaction between nitrogen monoxide and oxygen to form nitrogen dioxide.
   • Answer: $2NO + O_2 \rightarrow 2NO_2$
4. What is the role of nitrogen in plant growth?
   • Answer: Nitrogen is essential for the synthesis of amino acids and proteins in plants, thus promoting growth.
5. Define the term "nitrogen fixation."
   • Answer: Nitrogen fixation is the conversion of atmospheric nitrogen into compounds like ammonia that can be utilized by plants.

These revision notes provide a comprehensive overview of nitrogen and its compounds, covering important concepts and examples essential for KCSE preparation.