Question

Assign oxidation states for all atoms in each of the following compounds. a. \(U O_{2}^{2+}\) f. \(\mathrm{Mg}_{2} \mathrm{P}_{2} \mathrm{O}_{7}\) b. \(\mathrm{As}_{2} \mathrm{O}_{3}\) g. \(\mathrm{Na}_{2} \mathrm{S}_{2} \mathrm{O}_{3}\) c. \(\mathrm{NaBiO}_{3}\) h. \(\mathrm{Hg}_{2} \mathrm{Cl}_{2}\) d. \(\mathrm{As}_{4}\) i. \(\quad \mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}\) e. \(\mathrm{HAsO}_{2}\)

Short answer

Oxidation states for the given compounds: a. \(UO_{2}^{2+}\): U = +6, O = -2 b. \(As_{2}O_{3}\): As = +3, O = -2 c. \(NaBiO_{3}\): Na = +1, Bi = +5, O = -2 Note: Follow the same approach for the remaining compounds with their respective oxidation state rules.

Step-by-step solution

Identify the atoms and their oxidation number rules

Uranium (U) is a transition metal with variable oxidation states, and Oxygen (O) generally has an oxidation state of -2.

Assign oxidation states

Since the oxygen has an oxidation state of -2 and there are two oxygen atoms, the total negative charge is -4. The compound's overall charge is +2, so the Uranium must have a +6 oxidation state to balance it. Oxidation states: U = +6, O = -2 **Compound b: \(\mathrm{As}_{2} \mathrm{O}_{3}\)**

Identify the atoms and their oxidation number rules

Arsenic (As) belongs to Group 15 and often has oxidation states of +3 or +5, and Oxygen (O) generally has an oxidation state of -2.

Assign oxidation states

Again, Oxygen has an oxidation state of -2, so the total negative charge is -6 from three oxygen atoms. To balance this, each Arsenic atom will have an oxidation state of +3. Oxidation states: As = +3, O = -2 **Compound c: \(\mathrm{NaBiO}_{3}\)**

Identify the atoms and their oxidation number rules

Sodium (Na) always has an oxidation state of +1; Bismuth (Bi) belongs to Group 15 and often has oxidation states of +3 or +5; Oxygen (O) generally has an oxidation state of -2.

Assign oxidation states

With Sodium having an oxidation state of +1 and Oxygen -2, the total positive charge is +1, and the total negative charge is -6. Bismuth must have an oxidation state of +5 to balance the compound. Oxidation states: Na = +1, Bi = +5, O = -2 Additional compounds can be solved similarly, using the rules for assigning oxidation states: - Mg = +2 (alkaline earth metal) - P = +5 (compound is Mg2P2O7) - H = +1 - Hg = +1 (compound is Hg2Cl2) - Ca = +2 (alkaline earth metal) - N = +5 (compound is Ca(NO3)2)

Key concepts

Oxidation Number Rules

Understanding oxidation number rules is essential when studying chemistry, particularly in redox reactions. An oxidation number, often referred to as an oxidation state, is a number assigned to an element in a chemical compound that represents the number of electrons lost or gained by an atom of that element in the compound. Here's a simplification of the main rules you need to remember:

• The oxidation state of a pure element is always zero.
• For monatomic ions, the oxidation state is equal to the ion's charge.
• Oxygen usually has an oxidation state of -2, except in peroxides like H₂O₂ where it's -1, and in compounds with fluorine, where it may be positive.
• Hydrogen generally has an oxidation state of +1 when bonded to non-metals, and -1 when bonded to metals.
• The sum of oxidation states in a neutral compound must be zero; in a polyatomic ion, it must equal the ion's charge.

These rules help to assign oxidation states in complex compounds. For instance, in the given compound \( Mg_2 P_2 O_7 \), magnesium (Mg), as an alkaline earth metal, has a consistent oxidation state of +2. Phosphorus (P) can have various oxidation states, but when calculating with the known oxidation state of oxygen at -2, it becomes apparent that phosphorus must have a +5 oxidation state to satisfy the rule where the sum of oxidation states equals the charge of the compound, which in this case, is neutral.

Chemical Nomenclature

Chemical nomenclature is the systematic process of naming chemical compounds. It provides a unique and unequivocal means of identifying a chemical substance or compound. With a plethora of compounds in chemistry, nomenclature helps to avoid confusion and simplify communication among scientists. Here are critical aspects of nomenclature you should be familiar with:

• IUPAC nomenclature: This is a standardized naming convention developed by the International Union of Pure and Applied Chemistry (IUPAC).
• Cation and anion names: In ionic compounds, the cation (positive ion) name comes first, followed by the anion (negative ion).
• Prefixes and suffixes: Different groups attached to the central atom can change a compound’s name, often indicated by prefixes (e.g., mono-, di-, tri-) and suffixes (e.g., -ate, -ide).
• Functional groups: Specific groups of atoms within molecules that are responsible for characteristic chemical reactions of those molecules.

Using chemical nomenclature, the compound \( Ca(NO_3)_2 \) is named calcium nitrate. \(Ca\) is a calcium cation with a +2 charge, and the nitrate \( NO_3^- \) is an anion with a -1 charge. Since there are two nitrates for each calcium, the name reflects the 1:2 ratio of calcium ions to nitrate ions.

Balancing Redox Equations

Balancing redox equations is a fundamental aspect of chemical education, allowing one to account for the conservation of mass and charge. In redox reactions, elements undergo changes in oxidation number, reflecting a transfer of electrons between species. Here are the guidelines for balancing redox equations:

• Identify the oxidation states of the atoms involved in the reaction.
• Determine which elements are oxidized (increase in oxidation state) and which are reduced (decrease in oxidation state).
• Write separate half-reactions for the oxidation and reduction processes.
• Balance the number of electrons lost in the oxidation half-reaction with the number of electrons gained in the reduction half-reaction.
• Combine the half-reactions, ensuring that the overall charge and mass are balanced.

For instance, in the reduction of bismuth in \( NaBiO_3 \), bismuth goes from an oxidation state of +5 to a lower state (if it were part of a redox reaction), signifying it is being reduced. When balancing the redox equation involving \( NaBiO_3 \) as a reactant, one would balance the oxidation states change with the appropriate number of electrons and ensure both mass and charge are conserved in the final balanced equation.