Problem 84 - Chemistry and Chemical Reactivity

Question

Identify, from each list below, the compound or compounds that will dissolve in water to give a solution that strongly conducts electricity. (a) \(\mathrm{CuCO}_{3}, \mathrm{Cu}(\mathrm{OH})_{2}, \mathrm{CuCl}_{2}, \mathrm{CuO}\) (b) \(\mathrm{HCl}, \mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}, \mathrm{H}_{3} \mathrm{PO}_{4}, \mathrm{H}_{2} \mathrm{SO}_{4}\)

Step-by-Step Solution

Answer

(a) \( \mathrm{CuCl}_{2} \); (b) \( \mathrm{HCl}, \mathrm{H}_{2} \mathrm{SO}_{4} \).

Step 1: Understanding Electrical Conductivity in Solutions

Compounds that dissolve in water to form solutions that strongly conduct electricity must dissociate into ions. These solutions are known as strong electrolytes. Strong electrolytes typically include soluble salts, strong acids, and strong bases.

Step 2: Analyzing List (a) Compounds

Review the given compounds in list (a): 1. \( \mathrm{CuCO}_{3} \): Typically insoluble in water.2. \( \mathrm{Cu(OH)}_{2} \): Typically insoluble in water.3. \( \mathrm{CuCl}_{2} \): Soluble in water and dissociates into \( \mathrm{Cu}^{2+} \) and \( \mathrm{Cl}^{-} \) ions, thus a strong electrolyte.4. \( \mathrm{CuO} \): Typically insoluble in water.Therefore, \( \mathrm{CuCl}_{2} \) is the compound that will dissolve in water to form a solution that strongly conducts electricity.

Step 3: Analyzing List (b) Compounds

Review the given compounds in list (b): 1. \( \mathrm{HCl} \): A strong acid that dissociates completely into \( \mathrm{H}^{+} \) and \( \mathrm{Cl}^{-} \) ions.2. \( \mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4} \): Weak acid, does not fully dissociate.3. \( \mathrm{H}_{3} \mathrm{PO}_{4} \): Weak acid, does not fully dissociate.4. \( \mathrm{H}_{2} \mathrm{SO}_{4} \): A strong acid that dissociates completely into \( \mathrm{H}^{+} \) and \( \mathrm{HSO}_{4}^{-} \) ions initially.Therefore, \( \mathrm{HCl} \) and \( \mathrm{H}_{2} \mathrm{SO}_{4} \) are the compounds that will dissolve in water to form solutions that strongly conduct electricity.

Key Concepts

Strong Electrolytes

Not all compounds that dissolve in water make good electrical conductors. Strong electrolytes are special because they dissociate fully in water, breaking into positive and negative ions.
These ions are what carry electrical current through the solution.
A few common types of strong electrolytes include:

• Soluble salts, like sodium chloride \((\mathrm{NaCl})\).
• Strong acids, such as hydrochloric acid \((\mathrm{HCl})\).
• Strong bases, like sodium hydroxide \((\mathrm{NaOH})\).

This complete dissociation is crucial because it allows for a high concentration of ions, which in turn, makes the solution a good conductor of electricity.
Understanding which compounds are strong electrolytes helps predict their behavior once they are in a solution.

Ion Dissociation

Ion dissociation is a crucial part of understanding how electrolytes work.
When a compound dissolves in water and dissociates, it breaks into ions.
For example, when sodium chloride \((\mathrm{NaCl})\) dissolves, it separates into sodium ions \((\mathrm{Na}^+)\) and chloride ions \((\mathrm{Cl}^-) \).
The extent to which a compound dissociates in solution tells us a lot about its electrolyte strength:

• Complete dissociation: This happens with strong electrolytes. All the solute dissolves and splits into ions. Strong acids, bases, and most salts do this.
• Partial dissociation: Found in weak electrolytes. Only some of the solute forms ions, while the rest stays as molecules. Weak acids and bases fall into this category.

The more ions present in solution, the better its capacity to conduct electricity.
Therefore, understanding ion dissociation is key to predicting the electrical conductivity of a solution.

Solubility in Water

Solubility refers to how well a substance can dissolve in water.
This characteristic directly affects a compound's potential to act as a strong electrolyte.
Not all substances dissolve equally well. Here's how solubility differences affect solutions:

• Soluble compounds: These dissolve completely and can produce ions if they are electrolytes, leading to good conductivity.
• Insoluble compounds: These barely dissolve, meaning few or no ions are formed, leading to poor conductivity. Examples include most carbonates like \(\mathrm{CuCO}_3\).

Solubility is affected by the nature of the compound and the temperature of the water.
Knowing which compounds are soluble in water helps identify potential strong electrolytes.
This makes it a vital concept in chemistry, especially when predicting the behavior of substances in water.

Electrical Conductivity in Solutions

The ability of a solution to conduct electricity depends on ion presence.
When these ions are present, they move through the solution, carrying electric current.
Several factors influence a solution's conductivity:

• Ion concentration: More ions mean better conductivity. Strong electrolytes, which dissociate completely, provide more ions.
• Ion types: The type of ions can affect conductivity. For instance, even as a single ion, \(\mathrm{H}^+\) in acids like \(\mathrm{HCl}\) contributes significantly to conductivity.
• Temperature: Warmer solutions allow ions to move more freely, increasing conductivity.

Practical applications of electrical conductivity include determining ion concentration in laboratories and ensuring the quality of water in various industries.
Understanding this concept assists in identifying which solutions are capable of conducting electricity efficiently.