Question

Write the chemical formula for each of the following compounds, and indicate the oxidation state of nitrogen in each: (a) sodium nitrite, (b) ammonia, (c) nitrous oxide, (d) sodium cyanide, (e) nitric acid, (f) nitrogen dioxide.

Short answer

(a) Sodium nitrite: NaNO_2; oxidation state of nitrogen: +3. (b) Ammonia: NH_3; oxidation state of nitrogen: -3. (c) Nitrous oxide: N_2O; oxidation state of nitrogen: +1. (d) Sodium cyanide: NaCN; oxidation state of nitrogen: +2. (e) Nitric acid: HNO_3; oxidation state of nitrogen: +5. (f) Nitrogen dioxide: NO_2; oxidation state of nitrogen: +4.

Step-by-step solution

(a) Sodium nitrite

Sodium nitrite is composed of the sodium ion (Na^+) and the nitrite ion (NO_2^-). The chemical formula for sodium nitrite is NaNO_2. To find the oxidation state of nitrogen in NO_2^-, we can apply the oxidation state rules: - The oxidation state of oxygen is usually -2. - The sum of the oxidation states of all atoms in a compound must equal its charge. Let x be the oxidation state of nitrogen. Then we have: x + 2(-2) = -1 x = +3 So, the oxidation state of nitrogen in sodium nitrite is +3.

(b) Ammonia

Ammonia is composed of one nitrogen atom (N) and three hydrogen atoms (H). The chemical formula for ammonia is NH_3. To find the oxidation state of nitrogen, we apply the rules again: - The oxidation state of hydrogen is usually +1. - The sum of the oxidation states of all atoms in a neutral compound must equal zero. Let x be the oxidation state of nitrogen. Then we have: x + 3(+1) = 0 x = -3 So, the oxidation state of nitrogen in ammonia is -3.

(c) Nitrous oxide

Nitrous oxide, also known as laughing gas, is composed of two nitrogen atoms (N) and one oxygen atom (O). The chemical formula for nitrous oxide is N_2O. To find the oxidation state of nitrogen, we apply the rules: - The oxidation state of oxygen is usually -2. Let x be the oxidation state of nitrogen. Then we have: 2x + (-2) = 0 2x = +2 x = +1 So, the oxidation state of nitrogen in nitrous oxide is +1.

(d) Sodium cyanide

Sodium cyanide is composed of the sodium ion (Na^+) and the cyanide ion (CN^-). The chemical formula for sodium cyanide is NaCN. To find the oxidation state of nitrogen in CN^-, we apply the oxidation state rule: - The sum of the oxidation states of all atoms in a compound/ion must equal its charge. Let x be the oxidation state of nitrogen. Then we have: x + (-3) = -1 x = +2 So, the oxidation state of nitrogen in sodium cyanide is +2.

(e) Nitric acid

Nitric acid is composed of one nitrogen atom (N), one hydrogen atom (H), and three oxygen atoms (O). The chemical formula for nitric acid is HNO_3. To find the oxidation state of nitrogen, we apply the rules: - The oxidation state of hydrogen is usually +1. - The oxidation state of oxygen is usually -2. Let x be the oxidation state of nitrogen. Then we have: x + (+1) + 3(-2) = 0 x -5 = 0 x = +5 So, the oxidation state of nitrogen in nitric acid is +5.

(f) Nitrogen dioxide

Nitrogen dioxide is composed of one nitrogen atom (N) and two oxygen atoms (O). The chemical formula for nitrogen dioxide is NO_2. To find the oxidation state of nitrogen, we apply the rules: - The oxidation state of oxygen is usually -2. Let x be the oxidation state of nitrogen. Then we have: x + 2(-2) = 0 x = +4 So, the oxidation state of nitrogen in nitrogen dioxide is +4.

Key concepts

Oxidation States

Understanding oxidation states is crucial for identifying how atoms within a molecule or ion share their electrons. The oxidation state, or oxidation number, represents the number of electrons an atom gains or loses when forming a compound. Several rules help determine the oxidation states:

• The oxidation state of a free element (uncombined element) is always zero. For example, N₂ in the atmosphere.
• For a simple (monatomic) ion, the oxidation state is equal to the charge of the ion, such as Na⁺ which has an oxidation state of +1.
• Oxygen has an oxidation state of -2 in most of its compounds. An exception is peroxides, where the oxidation state is -1.
• Hydrogen generally has an oxidation state of +1, unless it is combined with metals in metal hydrides, such as in NaH, where it is -1.

The oxidation state helps predict how atoms will behave in chemical reactions and how they might combine with other atoms.

Inorganic Compounds

Inorganic compounds are substances not primarily based on carbon, unlike organic compounds. They include salts, minerals, and metals, often featuring ionic or covalent bonds. Inorganic chemistry is a vast field that covers everything from simple molecules like water (H₂O) to complex substances such as the minerals found in the Earth's crust.
Some common characteristics of inorganic compounds include:

• Simplicity of structure compared to organic compounds.
• A focus on metallic elements, gases like oxygen and hydrogen, and other non-metal elements.
• Often involve ionic bonding, where electrons are transferred between atoms, resulting in charged ions.
• Compounds like salts (e.g., sodium nitrite NaNO₂), and acids (e.g., nitric acid HNO₃).

Understanding inorganic compounds is key to comprehending a vast array of chemical reactions and their applications in the real world.

Chemical Nomenclature

Chemical nomenclature is the system of naming chemical compounds and is essential for clear communication in science. The International Union of Pure and Applied Chemistry (IUPAC) sets the rules for nomenclature to ensure consistency.
The nomenclature covers both organic and inorganic chemistry but focuses here on inorganic compounds:

• Simple ionic compounds are named by stating the cation (positive ion) first and the anion (negative ion) second. For instance, NaNO₂ is named sodium nitrite.
• For molecules consisting of non-metals, prefixes indicate how many atoms of each element are present, such as in N₂O, which is called dinitrogen monoxide.
• Acids are named based on their anions. For example, if the anion does not contain oxygen, the acid is named with the prefix "hydro-", and the suffix "-ic" attached to the root of the anion's name, such as hydrochloric acid for HCl.

Learning chemical nomenclature enables students to decipher the composition and structure of the compound from its name, aiding in understanding its properties and reactions.

Chemical Reactions

Chemical reactions occur when the substances you start with (reactants) transform into new substances (products). Understanding reactions is fundamental for grasping how chemical processes work.
Here are some basic principles of chemical reactions:

• Reactions involve breaking and forming chemical bonds. Bonds in the reactants are broken, and new bonds form in the products.
• Reactions can be classified into different types, such as synthesis (combining elements or compounds), decomposition (breaking down compounds), single or double displacement, and redox reactions (involving transfer of electrons).
• The rate of reaction and equilibrium affect how quickly and completely reactions occur, influencing yields.
• For instance, when nitrogen dioxide (NO₂) forms from nitrogen and oxygen, it involves a complex interplay of energy, bond formation, and oxidation states.

Chemical reactions are central to chemistry, allowing us to create new substances, harness energy, and understand natural processes.