Problem 32 - General Chemistry

Question

Using solubility rules, decide whether the following ionic solids are soluble or insoluble in water. If they are soluble, indicate what ions you would expect to be present in solution. a. \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\) b. \(\mathrm{BaCO}_{3}\) c. \(\mathrm{PbSO}_{4}\) d. \(\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}\)

Step-by-Step Solution

Answer

(NH4)2SO4 and Ca(NO3)2 are soluble; BaCO3 and PbSO4 are insoluble.

Step 1: Assess Solubility of (NH4)2SO4

According to solubility rules, all ammonium (\(\text{NH}_4^+\)) compounds are soluble in water. Therefore, \((\text{NH}_4)_2\text{SO}_4\) is soluble.

Step 2: Determine Ions for (NH4)2SO4

In solution, \((\text{NH}_4)_2\text{SO}_4\) dissociates into two \(\text{NH}_4^+\) ions and one \(\text{SO}_4^{2-}\) ion.

Step 3: Assess Solubility of BaCO3

Barium carbonate (\(\text{BaCO}_3\)) is generally insoluble in water according to solubility rules regarding carbonates, which are typically insoluble except for those associated with alkali metals and ammonium.

Step 4: Assess Solubility of PbSO4

Lead (II) sulfate (\(\text{PbSO}_4\)) is typically insoluble in water. While sulfates are generally soluble, notable exceptions include Pb, Ba, and Sr.

Step 5: Assess Solubility of Ca(NO3)2

Calcium nitrate (\(\text{Ca(NO}_3)_2\)) is soluble in water as nitrates of all elements are soluble without exception.

Step 6: Determine Ions for Ca(NO3)2

In solution, \(\text{Ca(NO}_3)_2\) dissociates into one \(\text{Ca}^{2+}\) ion and two \(\text{NO}_3^-\) ions.

Key Concepts

Ionic Solids

Ionic solids are substances composed of ions held together by ionic bonds. These ions are charged particles, either positive or negative, that result from the gain or loss of electrons. The ionic bonds that hold these ions together in a solid structure are usually strong, which contributes to the high melting and boiling points often observed in ionic compounds.
When an ionic solid is placed in water, it may dissolve, and its ions become solvated by water molecules. However, the solubility of ionic solids can vary significantly based on the nature of the ions present. Understanding solubility rules allows us to predict which ionic solids will dissolve in water and which will not, thus determining their behavior in aqueous solutions.

• Strong ionic bonds give ionic solids their high melting and boiling points.
• Solubility rules help predict whether an ionic solid will dissolve in water.
• Ionic solids typically dissociate into their constituent ions when soluble in water.

Ammonium Compounds

Ammonium compounds, containing the ammonium ion ( ext{NH}_4^+ ext{NH}_4^+), play a significant role in chemistry, particularly in solubility discussions. A key characteristic of ammonium compounds is their high solubility in water. This solubility can be attributed to the nature of the ammonium ion itself, which interacts effectively with water molecules, allowing these compounds to dissolve readily.
According to general solubility rules, nearly all compounds of ammonium are soluble. This means that when such a compound is added to water, it typically dissociates into ammonium ions and whatever other anion is present in the compound. This is helpful in predicting the behavior of these compounds in aqueous environments and when involved in chemical reactions.

• Ammonium compounds are generally soluble in water.
• The ammonium ion ( ext{NH}_4^+ ext{NH}_4^+) readily interacts with water molecules.
• Dissociation in solution helps in understanding chemical reactions and solubility.

Carbonates Solubility

Carbonates ( ext{CO}_3^{2-} ext{CO}_3^{2-}) are a class of compounds with distinct solubility characteristics. Generally, most carbonate compounds are insoluble in water. However, there are notable exceptions to this rule. Carbonates of alkali metals such as sodium and potassium, as well as those of ammonium, are soluble in water.
The insolubility of most carbonates arises from the strong ionic lattice they form, which does not easily dissociate in water. This aspect of their structure makes understanding the solubility rules crucial for predicting the behavior of carbonates in aqueous solutions. Knowledge of these exceptions helps chemists determine how different carbonate compounds will react in water.

• Most carbonate salts are insoluble, except for those with alkali metals and ammonium.
• The strong ionic lattice in carbonates prevents them from dissolving easily.
• Recognition of exceptions aids in predicting reactions involving carbonate compounds.

Sulfates Solubility

Sulfates ( ext{SO}_4^{2-} ext{SO}_4^{2-}) are another type of ionic compound with their own solubility characteristics. In general, sulfates are soluble in water; however, there are important exceptions that must be noted. Compounds containing lead, barium, and strontium, such as lead (II) sulfate, are exceptions and are typically insoluble.
This characteristic of sulfate solubility is due to the specific interactions between the sulfate ion and certain metal cations. While most sulfates will dissolve and dissociate into ions in water, knowing these exceptions helps chemists and students to accurately predict how sulfate compounds will behave, especially in chemical equations and reactions.

• Sulfates are usually soluble, with exceptions for compounds containing Pb, Ba, and Sr.
• The interactions between sulfate ions and certain metal ions impact solubility.
• Understanding these interactions aids in predicting the solubility of sulfate compounds.