Solubility Rules: Videos & Practice Problems

Solubility is a key chemical property that describes the ability of a solute to dissolve in a solvent, forming a solution. Understanding solubility involves distinguishing between two important terms: soluble and insoluble. A solute is considered soluble if it can dissociate into aqueous ions when mixed with a solvent. For example, when aluminum bromide (AlBr₃) is added to water, it dissolves and separates into its constituent ions: one aluminum ion (Al³⁺) and three bromide ions (Br^-). The aluminum ion, derived from group 3A of the periodic table, carries a +3 charge, while each bromide ion, from group 7A, carries a -1 charge. In solution, these ions are surrounded by water molecules, which is referred to as being in an aqueous state.

Conversely, a solute is classified as insoluble if it does not dissolve in a solvent. An example of this is silver bromide (AgBr), which remains intact and does not dissociate into ions when placed in water. This distinction is crucial for predicting the behavior of ionic compounds in various chemical reactions and solutions. In summary, soluble compounds break apart into aqueous ions, while insoluble compounds retain their structure and do not dissociate in solution.

When considering the soluble compound sodium sulfate, represented by the formula Na₂SO₄, it is essential to determine how many ions it produces when dissolved in water. Sodium sulfate dissociates into its constituent ions, which include two sodium ions and one sulfate ion. The dissociation can be expressed as:

Na₂SO₄ (s) → 2 Na⁺ (aq) + SO₄^2- (aq)

Here, each sodium ion (Na⁺) carries a +1 charge, and the sulfate ion (SO₄^2-) is a polyatomic ion with a -2 charge. Since sodium is located in Group 1A of the periodic table, it readily forms +1 ions. Therefore, when sodium sulfate dissolves, it produces a total of three ions: two sodium ions and one sulfate ion. This results in a final count of three ions in solution.

Solubility rules are essential guidelines that assist in predicting whether a compound will dissolve in water, which is crucial in various chemical reactions and processes. A helpful mnemonic to remember these rules is: "The bank robber was gonna cash his loot, but the cops stopped him." This phrase emphasizes key components of solubility.

In this mnemonic, "gonna cash" refers to the compounds that are generally soluble in water. For instance, most alkali metal salts (like sodium and potassium) and ammonium salts are soluble. Additionally, nitrates, acetates, and chlorates are also typically soluble. On the other hand, "cops" signifies the compounds that are generally insoluble, such as carbonates, phosphates, and sulfides, with some exceptions for alkali metals and ammonium.

Understanding these solubility rules is vital for predicting the behavior of ionic compounds in aqueous solutions, which can influence reaction outcomes, precipitate formation, and overall chemical interactions.

Ganache is a mnemonic used to identify soluble ionic compounds, while also highlighting exceptions that lead to the formation of precipitates, which are insoluble solids. The acronym stands for various groups and ions that are typically soluble in water.

The first letter, G, represents Group 1A elements, which include hydrogen, lithium, sodium, potassium, and others. These elements have no exceptions; any ionic compound containing them is automatically soluble.

The next letter, A, stands for the acetate ion (C₂H₃O₂^-), which is also always soluble when part of an ionic compound. Following this, N refers to the nitrate ion (NO₃^-), which similarly has no exceptions regarding solubility.

The second A in ganache represents the ammonium ion (NH₄⁺), which is soluble in all cases. The letter C stands for chlorate (ClO₃^-) and perchlorate (ClO₄^-), both of which are also soluble without exceptions.

The final letters, A and S, refer to sulfate (SO₄^2-) and halogens (Group 7A elements: fluorine, chlorine, bromine, and iodine). While sulfates are generally soluble, they have exceptions. To remember these exceptions, use the mnemonic CBS HAPI: if sulfate is paired with calcium (Ca), barium (Ba), strontium (Sr), or lead (Pb), it will form a precipitate. For halogens, they are soluble unless they are combined with mercury (Hg), silver (Ag), or lead (Pb), which will also result in a precipitate.

In summary, ganache serves as a helpful tool for identifying soluble ionic compounds, while also indicating specific exceptions that lead to the formation of precipitates. Understanding these rules is essential for predicting the solubility of various ionic compounds in aqueous solutions.

Understanding solubility rules is essential for predicting whether ionic compounds will dissolve in water. According to these rules, certain ions dictate the solubility of compounds. For instance, any compound containing a Group 1A element, such as sodium, is automatically soluble. This means that if sodium is present in an ionic compound, it will dissolve regardless of the other ions involved. Similarly, compounds containing nitrate ions are also soluble, as the presence of either ion guarantees solubility.

When examining calcium acetate, we find that acetate ions also confer solubility. Therefore, calcium acetate is soluble by default due to the presence of the acetate ion.

However, the case of barium sulfate is different. While sulfate ions are generally soluble, they have specific exceptions. The acronym CBS (Calcium, Barium, and Strontium) indicates that sulfates connected to these elements are insoluble. Since barium is part of this group, barium sulfate will not dissolve in water and will instead form a precipitate.

In contrast, compounds containing ammonium ions or perchlorate ions are soluble as well. Thus, when evaluating the solubility of the given ionic compounds, barium sulfate stands out as the only insoluble option, confirming it as a precipitate.

Understanding the solubility of ionic compounds is crucial in chemistry, particularly when dealing with insoluble ionic solutes. The acronym COPS helps to identify certain exceptions that lead to soluble aqueous ionic compounds. When we refer to COPS, we are specifically looking at the ions: Carbonate (C), Oxide (O), Phosphate (P), and Sulfide (S).

Starting with the letter C, which represents both the carbonate ion (CO₃^2-) and the chromate ion (CrO₄^2-), we note that these ions typically do not have exceptions and will form precipitates in most cases.

Moving to O, which stands for oxides (O^2-) and hydroxides (OH^-), we encounter exceptions. The solubility of these compounds increases when they are paired with calcium (Ca²⁺), barium (Ba²⁺), or strontium (Sr²⁺). This can be remembered with the phrase "CBS," indicating that oxides and hydroxides connected to these cations will dissolve in water, forming soluble aqueous compounds.

Next, P represents the phosphate ion (PO₄^3-), which, like carbonate, does not have exceptions and will generally form a precipitate.

Finally, S stands for sulfide (S^2-), which shares the same exceptions as oxides and hydroxides. Thus, sulfides will also be soluble when associated with calcium, barium, or strontium.

In summary, the COPS acronym serves as a helpful tool for predicting the solubility of ionic compounds. By remembering the exceptions associated with oxides and sulfides, students can effectively determine whether a compound will be soluble or insoluble in aqueous solutions.

When determining the solubility of various substances in water, it is essential to refer to specific solubility rules and exceptions. For hydroxide ions (OH^-), solubility is contingent upon their association with certain cations, specifically calcium (Ca²⁺), barium (Ba²⁺), or strontium (Sr²⁺). In this case, since aluminum (Al³⁺) is not part of the CBS (Calcium, Barium, Strontium) group, hydroxide connected to aluminum remains insoluble in water.

Next, considering phosphate ions (PO₄^3-), they typically do not have exceptions that would render them soluble unless paired with specific cations from the alkali metal group or ammonium (NH₄⁺). Since zinc (Zn²⁺) does not fall into these categories, the phosphate will also remain insoluble.

For silver (Ag⁺) combined with carbonate (CO₃^2-), the carbonate ion lacks exceptions that would allow for solubility in this context. As silver is not part of the alkali metals or ammonium, this combination will also be insoluble.

When evaluating sulfide ions (S^2-), it is important to note that they can be soluble when paired with calcium, barium, or strontium. Since sulfide is connected to calcium in this scenario, it becomes soluble in water.

Lastly, examining magnesium (Mg²⁺) with chromate (CrO₄^2-), chromate does not have exceptions that would allow for solubility, and magnesium is not part of the alkali metals or ammonium group. Therefore, this combination remains insoluble.

In summary, among the substances evaluated, only the sulfide ion connected to calcium is soluble in water, making it the sole option that forms a soluble ionic solute.