Problem 40 - Chemistry The Central Science In Si Units

Question

Select the more acidic member of each of the following pairs: (a) \(\mathrm{V}_{2} \mathrm{O}_{5}\) and VO, (b) \(\mathrm{Pb} \mathrm{O}\) and \(\mathrm{PbO}_{2}\), (c) \(\mathrm{N}_{2} \mathrm{O}_{3}\) and \(\mathrm{N}_{2} \mathrm{O}_{2},\) (d) \(\mathrm{SO}_{2}\) and \(\mathrm{SeO}_{2}\), (e) \(\mathrm{Al}_{2} \mathrm{O}_{3}\) and \(\mathrm{SeO}_{2},\) (f) \(\mathrm{CO}_{2}\) and \(\mathrm{B}_{2} \mathrm{O}_{3} .\)

Step-by-Step Solution

Answer

(a) \( \mathrm{V}_{2} \mathrm{O}_{5} \); (b) \( \mathrm{PbO}_{2} \); (c) \( \mathrm{N}_{2} \mathrm{O}_{3} \); (d) \( \mathrm{SeO}_{2} \); (e) \( \mathrm{SeO}_{2} \); (f) \( \mathrm{B}_{2} \mathrm{O}_{3} \).

Step 1: Understand the Concept of Acidic Oxides

To find which oxide is more acidic, remember that acid strength generally increases with the oxidation state of the central metal or non-metal. This is because higher oxidation states often lead to more polar bonds and greater ability to donate protons in water.

Step 2: Compare Oxidation States

Identify the oxidation states of the central atom in each oxide pair:- (a) In \( \mathrm{V}_{2} \mathrm{O}_{5} \) and \( \mathrm{VO} \), V has oxidation states \(+5\) and \(+2\) respectively.- (b) In \( \mathrm{PbO} \) and \( \mathrm{PbO}_{2} \), Pb has oxidation states \(+2\) and \(+4\) respectively.- (c) In \( \mathrm{N}_{2} \mathrm{O}_{3} \) and \( \mathrm{N}_{2} \mathrm{O} \), N has oxidation states \(+3\) and \(+2\) respectively.- (d) In \( \mathrm{SO}_{2} \) and \( \mathrm{SeO}_{2} \), oxidation states are \(+4\) for both.- (e) In \( \mathrm{Al}_{2} \mathrm{O}_{3} \) and \( \mathrm{SeO}_{2} \), oxidation states are \(+3\) for Al and \(+4\) for Se.- (f) In \( \mathrm{CO}_{2} \) and \( \mathrm{B}_{2} \mathrm{O}_{3} \), oxidation states are \(+4\) for C and \(+3\) for B.

Step 3: Analyze Acidic Strength Based on Oxidation State

- (a) \( \mathrm{V}_{2} \mathrm{O}_{5} \) is more acidic than \( \mathrm{VO} \) since +5 > +2.- (b) \( \mathrm{PbO}_{2} \) is more acidic than \( \mathrm{PbO} \) since +4 > +2.- (c) \( \mathrm{N}_{2} \mathrm{O}_{3} \) is more acidic than \( \mathrm{N}_{2} \mathrm{O} \) since +3 > +2.- (d) \( \mathrm{SeO}_{2} \) is slightly more acidic than \( \mathrm{SO}_{2} \) because Se has a larger atomic size, enhancing its acidic behavior.- (e) \( \mathrm{SeO}_{2} \) is more acidic than \( \mathrm{Al}_{2} \mathrm{O}_{3} \) due to the higher oxide state of Se and non-metallic nature.- (f) \( \mathrm{B}_{2} \mathrm{O}_{3} \) is more acidic than \( \mathrm{CO}_{2} \) due to the non-metallic nature and structure enhancing B's electron deficiency.

Key Concepts

Oxidation States

Oxidation states are key to understanding why certain compounds exhibit higher acidity. An oxidation state refers to the charge an atom would possess if the compound's bonding were entirely ionic. In simple terms, it helps indicate how many electrons an atom has gained or lost in forming a compound. Generally, a higher oxidation state in a central atom of an oxide corresponds to stronger acidic properties. This is because higher oxidation states tend to result in more polar bonds, making it easier for the compound to release protons when dissolved in water.

When comparing compounds like \( \mathrm{V}_{2} \mathrm{O}_{5} \) and \( \mathrm{VO} \), the oxidation state of Vanadium is +5 in \( \mathrm{V}_{2} \mathrm{O}_{5} \) and +2 in \( \mathrm{VO} \). Similarly, in \( \mathrm{PbO}_{2} \), Lead has a +4 oxidation state compared to a +2 state in \( \mathrm{PbO} \). These examples highlight the pattern of increased acidity with higher oxidation states.

Acid Strength

Acid strength in oxides is partly determined by how readily the oxide can donate protons in a chemical reaction, often when dissolved in water. Oxides of non-metals usually form acidic solutions because they can react with water to form acids. The ability to donate protons is greater when the oxide has a high oxidation state, due to the increased polarity of metal-oxygen bonds.

Consider the pairs \( \mathrm{N}_{2} \mathrm{O}_{3} \) and \( \mathrm{N}_{2} \mathrm{O} \), where \( \mathrm{N}_{2} \mathrm{O}_{3} \) is more acidic due to a higher oxidation state of +3 compared to +2. Similarly, \( \mathrm{SeO}_{2} \) showcases higher acidity compared to \( \mathrm{SO}_{2} \), not only because of its oxidation state but also due to Selenium's larger atomic size enhancing acid strength. In essence, as oxidation states climb, the resulting increase in bond polarity supports stronger acid formation.

Non-metal Oxides

Non-metal oxides are special as they tend to form acidic solutions upon mixing with water, differentiating them from many metal oxides. These compounds are formed when non-metals bond with oxygen, typically resulting in a molecule predisposed to ionization and proton donation.

In the cases mentioned, such as \( \mathrm{SeO}_{2} \) and \( \mathrm{CO}_{2} \), their status as non-metal oxides allows them to effectively form acids. Non-metal oxides like \( \mathrm{B}_{2} \mathrm{O}_{3} \) show significant acidity due to Boron's inconsistent electron sharing, contributing to a more acidic solution than an oxide like \( \mathrm{CO}_{2} \). In analyzing non-metal oxides, their chemical structure and tendency to form acidic compounds in aqueous solutions underscore their significance in understanding acidity trends in chemistry.