Question

Which of the following is not soluble in aq. \(\mathrm{NaOH}\) ?

Short answer

It's not possible to provide a short answer without a list of substances given in the exercise. However, to determine which substance is not soluble in aqueous NaOH, apply the solubility rules for bases: most hydroxides are insoluble, except those of Group 1 elements (alkali metals), Group 2 elements (from calcium downwards), and some amphoteric hydroxides. Once you have a list of substances, apply these rules to identify the insoluble substance.

Step-by-step solution

List the given substances

List the substances that are given in the exercise, so we can analyze their solubility in aqueous NaOH. The exercise does not provide a list of substances, so it's not possible to provide the exact solution step-by-step. However, we can still provide a general approach to solving similar problems.

Recall the solubility rules

Recall the general solubility rules for bases: 1. Most hydroxides are insoluble, but those of Group 1 elements (alkali metals) and Group 2 elements (from calcium downwards) are soluble. 2. Hydroxides of transition metals and post-transition metals are usually insoluble, except for some amphoteric hydroxides (e.g., \(\mathrm{Al(OH)_3}\) and \(\mathrm{Pb(OH)_2}\)) that can dissolve in both acidic and basic solutions.

Apply the solubility rules

For the given substances, determine their solubility in aqueous NaOH by applying the solubility rules. Keep in mind the amphoteric hydroxides that can dissolve in both acidic and basic solutions.

Identify the insoluble substance

Based on the solubility rules and the given substances, identify the substance that is not soluble in aqueous NaOH. Since the exercise did not provide a list of substances, we have followed a general approach to solving problems of this type. Once provided with a list of substances, simply apply the solubility rules described above, and you will be able to determine which substance is not soluble in aqueous NaOH.

Key concepts

aqueous NaOH

Aqueous NaOH, or sodium hydroxide in solution, is a key player in chemistry known for its strong basic properties. When dissolved in water, NaOH completely dissociates into sodium ions (\(\text{Na}^+\)) and hydroxide ions (\(\text{OH}^-\)). These ions are what give NaOH its high solubility in water and its typical characteristics as a strong base.

This solution is widely used in laboratories and industries for various applications, including pH regulation and chemical synthesis. In the context of solubility, aqueous NaOH is unique because it not only dissolves ionic compounds like bases but can also react with amphoteric substances.

Amphoteric substances are capable of reacting with both acids and bases, which means NaOH can sometimes dissolve them contrary to what might be expected given their typical insolubility.

amphoteric hydroxides

Amphoteric hydroxides are fascinating substances because they defy the common solubility rules. These are compounds that can act both as acids and bases, allowing them to dissolve in solutions of strong acids and strong bases like NaOH.

Notable examples of amphoteric hydroxides include aluminum hydroxide \(\text{Al(OH)}_3\) and lead hydroxide \(\text{Pb(OH)}_2\). When placed in a basic solution such as aqueous NaOH, these crystals can dissociate and form complex compounds, which makes them soluble in such conditions.

Their dual nature offers interesting pathways in chemical reactions, making them valuable in different industrial and laboratory processes.

group 1 elements

Elements found in Group 1 of the periodic table are known as alkali metals. These include lithium, sodium, potassium, rubidium, cesium, and francium.

A characteristic feature of these elements is their ability to form highly soluble hydroxides. For instance, sodium forms NaOH, which is readily soluble in water. This is because alkali metals have a single electron in their outer shell, which makes them highly reactive and capable of easily forming ionic compounds with hydroxide ions.

Due to their reactivity and solubility, they are often used in chemical solutions to create strong bases in scientific experiments and industrial processes.

group 2 elements

Group 2 elements are referred to as alkaline earth metals and include beryllium, magnesium, calcium, strontium, barium, and radium.

Unlike Group 1, the solubility of their hydroxides in water varies. Generally, hydroxides of calcium, strontium, and barium become more soluble as you move down the group. This is due to the structure and nature of their ionic compounds, which influences how they interact in aqueous solutions. Typically, beryllium and magnesium hydroxides are less soluble, a notable exception to this trend.

This solubility behavior is critical in solving chemistry problems as it determines how these substances behave in different chemical environments.

chemistry problem-solving

Solving chemistry problems, particularly those involving solubility, requires a good understanding of the fundamental rules and principles that dictate how substances interact.

Here are some key steps to follow:

• Identify the chemical compounds involved and their respective groups in the periodic table.
• Review the general solubility rules, especially for hydroxides, to predict their behavior in a given solution like aqueous NaOH.
• Consider exceptions such as amphoteric hydroxides, which might dissolve despite typical rules.
• Apply logic and reasoning based on chemical principles to determine the expected outcomes in reactions.

Practicing these approaches strengthens problem-solving skills and fosters a deeper understanding of chemistry.