Question

Which member of each pair produces the more acidic aqueous solution: \((\mathbf{a}) \mathrm{Zn} \mathrm{Br}_{2}\) or \(\mathrm{CdCl}_{2},\) (b) \(\mathrm{CuCl}\) or \(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}\), (c) \(\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}\) or \(\mathrm{NiBr}_{2} ?\)

Short answer

1. CdCl₂ produces a more acidic aqueous solution than ZnBr₂. 2. CuCl and Cu(NO₃)₂ produce solutions with similar acidity. 3. NiBr₂ produces a more acidic aqueous solution than Ca(NO₃)₂.

Step-by-step solution

Compare ZnBr₂ and CdCl₂#aсidity#

In order to compare the acidity of the resulting solutions when ZnBr₂ and CdCl₂ are dissolved in water, let's look at the elements involved: Zn, Cd, Br, and Cl. The acidity of their solutions will depend on their ability to release H⁺ ions when they form a solution. ZnBr₂ dissolves in water to form Zn²⁺ and 2Br⁻ ions, while CdCl₂ dissolves in water to form Cd²⁺ and 2Cl⁻ ions. Since both bromide and chloride ions are weak bases, we will focus on the cations – Zn²⁺ and Cd²⁺. Comparing their positions in the periodic table, Cd is immediately below Zn in the same group and has a larger atomic radius, so it forms weaker bonds with the surrounding water molecules. Hence, Cd²⁺ ions will have a higher tendency to donate a proton (H⁺) to the water molecules to form hydronium ions (H₃O⁺), which increases the acidity of the solution. Therefore, CdCl₂ produces a more acidic aqueous solution than ZnBr₂. 2.

Compare CuCl and Cu(NO₃)₂ acidity#

Both compounds result in the formation of Cu²⁺ ions when dissolved in water. In the case of CuCl, it will form Cu²⁺ and Cl⁻ ions, while Cu(NO₃)₂ will form Cu²⁺ and 2NO₃⁻ ions. Chloride and nitrate ions are weak bases and minimally impact the acidity of the solution. Since both compounds result in the formation of Cu²⁺ ions, neither one is more acidic than the other. CuCl and Cu(NO₃)₂ will produce solutions with similar acidity. 3.

Compare Ca(NO₃)₂ and NiBr₂ acidity#

When dissolved in water, Ca(NO₃)₂ will form Ca²⁺ and 2NO₃⁻ ions, while NiBr₂ will form Ni²⁺ and 2Br⁻ ions. The acidity of the resulting solutions again depends on their ability to release H⁺ ions. Nitrate and bromide ions are weak bases, so we will focus on the cations – Ca²⁺ and Ni²⁺. Comparing their positions in the periodic table, Ca is an alkaline earth metal located in Group 2, while Ni is a transition metal located in Group 10. Alkaline earth metals, like Ca, typically form basic oxides when they react with oxygen, whereas transition metals, like Ni, can form amphoteric oxides. Since amphoteric oxides can both donate and accept protons (H⁺), the Ni²⁺ ions would have a higher tendency to donate a proton (H⁺) to the water molecules, which will result in a more acidic solution. Therefore, NiBr₂ produces a more acidic aqueous solution than Ca(NO₃)₂. #Summary# 1. CdCl₂ produces a more acidic aqueous solution than ZnBr₂. 2. CuCl and Cu(NO₃)₂ produce solutions with similar acidity. 3. NiBr₂ produces a more acidic aqueous solution than Ca(NO₃)₂.

Key concepts

Cation Acidity

Cation acidity is an important factor when determining the acidity of a solution. In simple terms, a cation is a positively charged ion, and its ability to make a solution more acidic depends on how readily it donates protons (H⁺ ions) to water.

When a cation dissolves in water, it interacts with water molecules. The strength of these interactions is influenced by properties such as the cation's charge and size. Generally, cations with a higher charge or smaller size tend to be more strongly polarized and can more easily donate H⁺ ions.

This proton donation increases the concentration of hydronium ions (H₃O⁺) in the solution, making it more acidic. Understanding these interactions helps explain why certain cations make aqueous solutions more acidic than others.

Periodic Table and Acidity

The position of a chemical element on the periodic table can give significant insights into its acidity characteristics. The periodic table is arranged in a way that groups elements with similar properties together. Generally, acidity can increase with elements located further down a group because they possess larger atomic radii.

For example, in the exercise, cadmium (Cd) is located below zinc (Zn). Because Cd has a larger size, its ions form weaker bonds with water, facilitating the release of H⁺ ions and thus creating a more acidic environment.

When comparing elements within the same group or period, these trends provide strong clues in predicting which might produce a more acidic solution upon dissolution.

Comparison of Ionic Compounds

When analyzing the acidity of ionic compounds, it's crucial to consider not only the cations and their interactions with water, but also the nature of the accompanying anions.

For instance, chloride and bromide ions in solutions are weak bases, meaning they do not significantly affect the solution's acidity. Thus, when comparing ionic compounds, the focus is primarily on the cations.

In cases like CuCl and Cu(NO₃)₂, the resultant Cu²⁺ ions are the primary determinants of the acidity, since chloride and nitrate anions don’t contribute significantly to the acidity level. However, if an anion itself were acidic or basic, it could also influence the overall acidity of the solution.

Acid-Base Chemistry

Acid-base chemistry explores the reactions and interactions involving acids and bases. In aqueous solutions, acids donate protons (H⁺ ions) while bases accept them. The degree to which these interactions occur can vary greatly, impacting the solution's pH level.

The study of these reactions often includes examining the resulting ions and how they interact with water molecules. Strong acids completely ionize in water, releasing more H⁺ ions, thus making the solution more acidic. Conversely, weak acids only partially ionize, contributing less to the overall acidity.

In the exercise context, understanding these principles allows us to predict and compare the acidity of various ionic compounds when they dissolve. Knowing the nature of the cations and anions involved, along with the acid-base behavior, is key to mastering this aspect of chemistry.