Question

Assign oxidation numbers to the atoms in each substance. a) \(\mathrm{CH}_{2} \mathrm{O}\) b) \(\mathrm{NH}_{3}\) c) \(\mathrm{Rb}_{2} \mathrm{SO}_{4}\) d) \(\mathrm{Zn}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right) 2\)

Short answer

a) C: 0, H: +1, O: -2; b) N: -3, H: +1; c) Rb: +1, S: +6, O: -2; d) C: 0, H: +1, O: -2, Zn: +2.

Step-by-step solution

Assign oxidation numbers in CH₂O

In formaldehyde, \( \mathrm{CH}_2\mathrm{O} \), the oxidation number of hydrogen is +1 and oxygen is -2. Let x be the oxidation number of carbon. The sum of the oxidation numbers must equal 0.\[x + 2(+1) + (-2) = 0\] Simplifying, we find x = 0; hence, the oxidation numbers are:- C: 0 - H: +1 - O: -2.

Assign oxidation numbers in NH₃

For ammonia, \( \mathrm{NH}_3 \), the oxidation number of hydrogen is +1. Let y be the oxidation number of nitrogen. The sum of the oxidation numbers must equal 0.\[y + 3(+1) = 0\] Simplifying, we find y = -3; hence, the oxidation numbers are:- N: -3 - H: +1.

Assign oxidation numbers in Rb₂SO₄

In \( \mathrm{Rb}_2\mathrm{SO}_4 \), rubidium is an alkali metal with oxidation number +1 and sulfate is known to have a charge of -2. For sulfur, let z be its oxidation number. The sum of the oxidation numbers must equal 0.\[2(+1) + z + 4(-2) = 0\] Simplifying, we find z = +6; hence, the oxidation numbers are:- Rb: +1 - S: +6 - O: -2.

Assign oxidation numbers in Zn(C₂H₃O₂)₂

Each acetate ion (\(\mathrm{C_2H_3O_2}^-\)) has a known charge of -1. Zinc typically has an oxidation number of +2. Assume each C in acetate has the unknown oxidation number a. Using previously known oxidation states; O is -2 and H is +1. The sum of the oxidation numbers per acetate ion equals -1: \[2a + 3(+1) + 2(-2) = -1\] Solving, \[2a = 0 \rightarrow a = 0\]. Overall, for acetate:- C: 0- H: +1- O: -2For Zn:- Zn: +2

Key concepts

Redox Reactions

A redox reaction involves the transfer of electrons between chemical species. These reactions are crucial in chemistry, as they involve two simultaneous processes: oxidation and reduction. Oxidation refers to the loss of electrons, often resulting in an increase in oxidation number, while reduction refers to the gain of electrons, leading to a decrease in oxidation number.

In the context of the given exercise, assigning oxidation numbers helps determine which atoms are oxidized and which are reduced during the reaction. For example, if a compound involves the conversion of **Formal Charge Calculation:** Oxidation numbers differ slightly from formal charges, as they provide a way to keep track of electrons in redox reactions rather than overall electron distribution in a molecule. This allows chemists to understand the flow of electrons in a reaction and to predict the reactivity of different molecules.

• Oxidation: Increase in oxidation number; loss of electrons.
• Reduction: Decrease in oxidation number; gain of electrons.
• Redox reactions occur when oxidation and reduction processes happen together.

Understanding this concept is essential for solving problems involving redox reactions, as it provides insight into the movement of electrons and helps predict the products of chemical changes.

Formal Charge Calculation

Calculating formal charges in molecules helps understand the distribution of electrons in a chemical compound. While oxidation numbers are assigned to help identify oxidation and reduction, formal charges are used to assess the most feasible Lewis structure by ensuring that electrons are assigned as evenly as possible across atoms in a molecule.

The formula to calculate the formal charge (FC) of an atom is:\[ \text{FC} = \left(\text{valence electrons}\right) - \left(\text{non-bonding electrons}\right) - \frac{1}{2}(\text{bonding electrons})\]

• Assign each atom in a molecule its formal charge to see if electron distribution makes sense.
• Lewis structures are validated through formal charge calculations.
• Formal charges should ideally be as close to zero as possible on each atom to increase stability.

Remember, the goal is to achieve the lowest energy structure, which is often where formal charges on the atoms are minimized. While assigning oxidation numbers is particularly aimed at tracking electron flow in redox reactions, formal charge calculations more broadly help map the electron landscape in molecules.

Chemical Compounds

Chemical compounds consist of two or more elements bonded together, resulting in a substance with distinct chemical properties. Each compound's behavior is determined by the elements' bonding and oxidation numbers. Simple rules help assign oxidation numbers, essential for analyzing redox reactions and balancing chemical equations.

• Understand typical oxidation numbers: Oxygen is usually -2; hydrogen is +1.
• Elements’ oxidation numbers in their stand-alone state (like Zn or O um__2__) are zero.
• The sum of oxidation numbers in a neutral compound must be zero.
• For polyatomic ions, the sum equals the overall charge of the ion.

In the context of this lesson, understanding how atoms in chemical compounds as in **Assigning Oxidation Numbers Methodology:** Chemical compounds is essential not only for solving redox equations but also for qualitative analysis of reactions. Recognizing patterns in oxidation numbers allows you to predict the type of chemical reactions and transformations a compound might undergo.