Problem 30 - Chemistry The Molecular Science

Question

Predict whether each compound is soluble in water. Indicate which ions are present in solution for the watersoluble compounds. (a) Ammonium nitrate (b) Barium sulfate (c) Potassium acetate (d) Calcium carbonate (e) Sodium perchlorate

Step-by-Step Solution

Answer

(a), (c), and (e) are soluble; (b) and (d) are insoluble.

Step 1: Understand Solubility Rules

To predict the solubility of compounds in water, we use general solubility rules. According to these rules: ammonium ( htags{NH_4^+} ), nitrate ( htags{NO_3^-} ), potassium ( htags{K^+} ), acetate ( htags{C_2H_3O_2^-} ), and sodium ( htags{Na^+} ) salts are typically soluble. Barium sulfate ( htags{BaSO_4} ) and calcium carbonate ( htags{CaCO_3} ) are typically insoluble.

Step 2: Analyze Each Compound

Evaluate the solubility based on the solubility rules: - (a) Ammonium nitrate contains ammonium and nitrate, both of which are soluble. - (b) Barium sulfate is commonly known to be insoluble. - (c) Potassium acetate is soluble due to the presence of potassium and acetate ions. - (d) Calcium carbonate is typically insoluble. - (e) Sodium perchlorate contains sodium, which is soluble.

Step 3: Identify Ions in Solution for Soluble Compounds

For the soluble compounds, identify the ions present: - (a) Ammonium nitrate: In solution, it dissociates into htags{NH_4^+} and htags{NO_3^-} ions. - (c) Potassium acetate: In solution, it dissociates into htags{K^+} and htags{C_2H_3O_2^-} ions. - (e) Sodium perchlorate: In solution, it dissociates into htags{Na^+} and htags{ClO_4^-} ions.

Key Concepts

Solubility Rules

Solubility rules are guidelines that help us predict whether an ionic compound will dissolve in water. These rules are derived from observations about how different ions behave in aqueous solutions. Understanding solubility rules is crucial in numerous chemical processes and applications.

Some general solubility rules include:

• Most nitrate (\(NO_3^-\)) salts are soluble.
• Salts containing alkali metal ions (like \(Na^+\), \(K^+\)) and the ammonium ion (\(NH_4^+\)) are typically soluble.
• Most chloride, bromide, and iodide salts are soluble, except for those containing silver, lead, and mercury ions.
• Most sulfate (\(SO_4^{2-}\)) salts are soluble, but calcium sulfate (\(CaSO_4\)), barium sulfate (\(BaSO_4\)), and lead sulfate are exceptions.
• Most carbonate (\(CO_3^{2-}\)) and phosphate (\(PO_4^{3-}\)) salts are insoluble, except those of sodium, potassium, and ammonium.

These rules are not without exceptions, but they offer a reliable starting point for predicting solubility in water.

Ionic Compounds

Ionic compounds are composed of positive (cation) and negative (anion) ions bonded together by electrostatic forces. This type of bonding is known as ionic bonding. Ionic compounds are usually formed between metals, which tend to lose electrons, and non-metals, which tend to gain electrons.

Characteristics of ionic compounds include:

• They generally have high melting and boiling points due to the strong attraction between ions.
• They are typically solid at room temperature.
• They conduct electricity when melted or dissolved in water, as ions are free to move.
• They are often soluble in water, yet some may be insoluble due to strong ionic bonds or insufficient interaction with water molecules.

In the context of solubility, understanding the nature of ionic bonds helps explain why certain substances like ammonium nitrate (\(NH_4NO_3\)) dissolve easily, releasing ions into solution, whereas others like barium sulfate (\(BaSO_4\)) do not.

Solution Chemistry

Solution chemistry focuses on the process of dissolving, where solutes (such as ionic compounds) are dispersed in solvents (usually water) to form a homogeneous mixture known as a solution. This concept is central to understanding chemical reactions and processes in aqueous environments.

When an ionic compound dissolves in water, it dissociates into its component ions. For example, when sodium perchlorate (\(NaClO_4\)) dissolves, it separates into sodium ions (\(Na^+\)) and perchlorate ions (\(ClO_4^-\)).

Key aspects of solution chemistry include:

• **Concentration:** Describes how much solute is present in a given quantity of solvent, affecting the physical and chemical properties of the solution.
• **Saturation:** Refers to the point at which no more solute can dissolve in the solvent at a given temperature and pressure.
• **Solubility:** The maximum amount of solute that can dissolve in a solvent at a specified temperature and pressure, guided by solubility rules.

Studying how different compounds dissolve and interact in solutions allows chemists to predict and control the outcomes of reactions, important for processes like pharmaceuticals, cleaning, and manufacturing.