Question

On the basis of the general solubility rules given in Table 4.1, predict which of the following substances are likely to be soluble in water. a. aluminum nitrate b. magnesium chloride c. rubidium sulfate d. nickel(II) hydroxide e. lead(II) sulfide f. magnesium hydroxide g. iron(III) phosphate

Short answer

Using the general solubility rules, the solubility predictions for the given compounds in water are: a. Aluminum nitrate: Soluble b. Magnesium chloride: Soluble c. Rubidium sulfate: Soluble d. Nickel(II) hydroxide: Insoluble e. Lead(II) sulfide: Insoluble f. Magnesium hydroxide: Insoluble g. Iron(III) phosphate: Insoluble

Step-by-step solution

Identify the Anions

Using the general solubility rules, we need to identify the anions in each of the given compounds. We have the following: a. Aluminum nitrate: Nitrate (NO_3^-) b. Magnesium chloride: Chloride (Cl^-) c. Rubidium sulfate: Sulfate (SO_4^2-) d. Nickel(II) hydroxide: Hydroxide (OH^-) e. Lead(II) sulfide: Sulfide (S^2-) f. Magnesium hydroxide: Hydroxide (OH^-) g. Iron(III) phosphate: Phosphate (PO_4^3-)

Apply Solubility Rules

Now, for each compound, we will check its solubility using the general solubility rules (Table 4.1). a. Aluminum nitrate: Nitrates are soluble with all cations. b. Magnesium chloride: Chlorides are soluble with all cations except silver (Ag^+), lead (Pb^2+), and mercury (Hg^2+). c. Rubidium sulfate: Sulfates are soluble with all cations except barium (Ba^2+), calcium (Ca^2+), strontium (Sr^2+), lead (Pb^2+), mercury (Hg^2+), and silver (Ag^+). d. Nickel(II) hydroxide: Hydroxides are insoluble with all cations except alkali metals, ammonium (NH_4^+), calcium (Ca^2+), and barium (Ba^2+). e. Lead(II) sulfide: Sulfides are insoluble with all cations except alkali metals and ammonium (NH_4^+). f. Magnesium hydroxide: Hydroxides are insoluble with all cations except alkali metals, ammonium (NH_4^+), calcium (Ca^2+), and barium (Ba^2+). g. Iron(III) phosphate: Phosphates are insoluble with all cations except alkali metals and ammonium (NH_4^+).

Provide Solubility Predictions

Based on the solubility rules from Table 4.1, we can predict the solubility of each compound in water: a. Aluminum nitrate: Soluble b. Magnesium chloride: Soluble c. Rubidium sulfate: Soluble d. Nickel(II) hydroxide: Insoluble e. Lead(II) sulfide: Insoluble f. Magnesium hydroxide: Insoluble g. Iron(III) phosphate: Insoluble

Key concepts

Solubility Predictions

Understanding solubility predictions in chemistry is fundamental for both students and professionals. It involves assessing whether a specific substance will dissolve in a solvent, such as water.

When presented with a compound, the first step in predicting solubility is to look at the ions it contains. For instance, compounds containing nitrate ions (\(NO_3^-\)) are generally soluble, no matter the cation they are paired with. This is why we can assert that aluminum nitrate is soluble in water. Similarly, magnesium chloride's components, magnesium (\(Mg^{2+}\)) and chloride (\(Cl^-\)), typically result in a soluble substance, as chlorides are soluble with most cations, with notable exceptions.

It is crucial to familiarize oneself with the exceptions to the solubility rules. For example, despite sulfates being widely soluble, rubidium sulfate's solubility is affirmed due to rubidium being an alkali metal, which typically forms soluble compounds. Understanding these guidelines allows chemists to anticipate reactions in clinical, environmental, or industrial settings.

General Solubility Rules

General solubility rules serve as a quick reference to predict the solubility of ionic compounds. Such rules are based on empirical observations and help determine if compounds will dissolve in water, aiding in various chemical applications.

Some cardinal directives include the solubility of nitrates, acetates, and most perchlorates with any cation. Alkali metal compounds and ammonium (\(NH_4^+\)) salts are also typically soluble. Conversely, compounds formed with common anions such as carbonate, phosphate, sulfate, and hydroxide are more selective, showing solubility with specific cations.

Taking magnesium hydroxide as an example, while hydroxides are usually insoluble, alkali metals and a small subset of other cations like (\(Ca^{2+}\)) and (\(Ba^{2+}\)) are exceptions. This systemic approach of learning solubility rules greatly simplifies the process of determining the behavior of chemicals in solution.

Compound Solubility

Compound solubility involves understanding how different chemicals—which are structured from various ions—interact with solvents. It's an essential concept in chemical solutions and influences outcomes in reactions.

For instance, even though sulfides have a general rule of being insoluble, when paired with either alkali metals or (\(NH_4^+\)), they break this trend, becoming soluble. Lead(II) sulfide is insoluble due to the general insolubility of sulfides and the absence of an overriding soluble cation. Similarly, nickel(II) hydroxide's insolubility highlights another aspect of solubility regarding metal hydroxides: only a few, associated with specific cations, dissolve in water.

When considering solubility, it's not just the rules that are important, but also the underlying reasons, such as the lattice energy of ionic solids and the solvation energy of ions in solution.

Anion Identification

Anion identification is a pivotal skill in chemistry, particularly when predicting compound solubility. An anion is a negatively charged ion, which often determines the general solubility of a compound when paired with a cation.

In the exercise provided, we see that the solubility of various substances is largely dependent on the anions present. For example, nitrates (\(NO_3^-\)), chlorides (\(Cl^-\)), and sulfates (\(SO_4^{2-}\)) generally lead to soluble compounds, unless matched with certain cations. On the other hand, hydroxides (\(OH^-\)), sulfides (\(S^{2-}\)), and phosphates (\(PO_4^{3-}\)) frequently form insoluble compounds, providing a quick way to predict solubility.

Recognizing anions and knowing their typical behavior helps chemists to predict outcomes without the need for extensive empirical testing, streamlining processes in laboratories and various industry applications.