Problem 99 - Chemistry: An Atoms-Focused Approach

Question

Sulfuric acid reacts with nitric acid as shown below: \(\mathrm{HNO}_{3}(a q)+2 \mathrm{H}_{2} \mathrm{SO}_{4}(a q) \rightarrow \mathrm{NO}_{2}^{+}(a q)+\mathrm{H}_{3} \mathrm{O}^{+}(a q)+2 \mathrm{HSO}_{4}^{-}(a q)\) a. Is the reaction a redox process? b. Identify the acid, base, conjugate acid, and conjugate base in the reaction. (Hint: Draw the Lewis structures for each.

Step-by-Step Solution

Answer

Identify the acid, base, conjugate acid, and conjugate base in the reaction. Answer: Yes, the reaction is a redox process. In the reaction, HNO3 acts as the acid, H2SO4 acts as the base, H3O+ is the conjugate acid, and NO2+ is the conjugate base.

Step 1: Identify the oxidation states of the elements.

Assign oxidation states for each element in the reactants and products. In this case, the oxidation states are as follows: \(\mathrm{HNO}_3\): H +1, N +5, O -2 \(\mathrm{H}_2\mathrm{SO}_4\): H +1, S +6, O -2 \(\mathrm{NO}_2^+\): N +4, O -2 \(\mathrm{H}_3\mathrm{O}^+\): H +1, O -2 \(\mathrm{HSO}_4^-\): H +1, S +6, O -2

Step 2: Compare the oxidation states.

Compare the oxidation states of the elements in the reactants and products to see if any elements have changed their oxidation states: The nitrogen in \(\mathrm{HNO}_3\) has an oxidation state of +5, and the nitrogen in \(\mathrm{NO}_2^+\) has an oxidation state of +4. The other elements have the same oxidation states in both reactants and products. Since the oxidation state of nitrogen changes during the reaction, we can conclude that this reaction is a redox process. Answer to (a): Yes, the reaction is a redox process. #b. Identify the acid, base, conjugate acid, and conjugate base in the reaction.#

Step 1: Analyze the Lewis structures.

Draw the Lewis structures for each species involved in the reaction to understand the electron distribution and potential sites for proton (H+) transfer: - HNO3 has a central N atom with three O atoms, where one O is directly bonded to an H atom. - H2SO4 has a central S atom with four O atoms, where two O atoms are directly bonded to H atoms. - NO2+ has a central N atom with two O atoms and a positive formal charge on N. - H3O+ has an O atom with three H atoms bonded to it and a positive formal charge on O. - HSO4- has a central S atom with four O atoms, where one O is directly bonded to an H atom and a negative formal charge on one of the O atoms.

Step 2: Identify the acid and base.

In the reaction, proton transfer occurs: - HNO3 donates a proton (H+) to H2SO4, which means HNO3 is acting as an acid. - H2SO4 accepts a proton (H+) from HNO3, which means H2SO4 is acting as a base.

Step 3: Identify the conjugate acid and conjugate base.

Once the proton transfer occurs: - HNO3 loses a proton and becomes NO2+ (the conjugate base). - H2SO4 gains a proton and becomes H3O+ and HSO4- (the conjugate acid). Answer to (b): - Acid: \(\mathrm{HNO}_3\) - Base: \(\mathrm{H}_2\mathrm{SO}_4\) - Conjugate acid: \(\mathrm{H}_3\mathrm{O}^+\) - Conjugate base: \(\mathrm{NO}_2^+\)

Key Concepts

Understanding Oxidation States

Oxidation states are vital for identifying how electrons are transferred in chemical reactions, making them crucial in understanding redox reactions. The oxidation state of an element in a compound indicates the number of electrons lost or gained compared to its neutral state.

• In the context of hydrogen and oxygen in compounds, hydrogen is typically +1 and oxygen is -2.
• Transition metals and nonmetals can have varying oxidation states which you determine by balancing the overall charge of the compound.

In the given reaction between sulfuric acid and nitric acid, determining the oxidation states of the elements helps to verify the redox nature of the reaction. We observe that nitrogen's oxidation state changes from +5 in \(\mathrm{HNO}_3\) to +4 in \(\mathrm{NO}_2^+\). This change confirms that a redox reaction has occurred, as electrons are transferred during this process. Identifying these changes helps us understand how the electron flow affects the chemistry involved.

Acid-Base Reactions: Proton Transfer

An acid-base reaction is primarily about the transfer of protons (H+ ions) from one species to another. During these reactions, acids donate protons, while bases accept them. This concept is grounded in the Brønsted-Lowry theory.

• Acids are proton donors.
• Bases are proton acceptors.
• Conjugate acids and bases are formed through the donation and acceptance of protons.

In the sulfuric and nitric acids reaction, \(\mathrm{HNO_3}\) donates a proton to \(\mathrm{H_2SO_4}\), indicating that \(\mathrm{HNO_3}\) is acting as an acid. Concurrently, \(\mathrm{H_2SO_4}\) accepts the proton, so it acts as a base. The species formed after proton donation is \(\mathrm{NO_2^+}\) (the conjugate base), while the proton-accepting species forms \(\mathrm{H_3O^+}\) and \(\mathrm{HSO_4^-}\) (the conjugate acid). Recognizing these roles clarifies the proton movements in acid-base reactions.

Understanding Lewis Structures

Lewis structures are diagrams that show the bonding between atoms of a molecule and any lone pairs of electrons that may exist. These structures allow us to visualize the arrangements and predict how molecules might interact in a reaction.

• Electrons are depicted as dots and bonds as lines between the atoms.
• Lone pairs or non-bonding electrons are shown as pairs of dots on individual atoms.
• Highlighting electronical interactions helps clarify roles in acid-base reactions.

In the reaction given, drawing Lewis structures for each involved compound helps illustrate their electronic arrangements and potential for interactions. For instance, \(\mathrm{HNO_3}\) has a central nitrogen atom that connects to three oxygen atoms, one of which also holds a hydrogen atom. This configuration shows areas where proton transfer may occur. By understanding these structures, we can recognize which molecules are more inclined to donate or accept protons, crucial for predicting the flow of protons and electrons during reactions.