Problem 28 - Chemistry The Molecular Science

Question

Which substance conducts electricity when dissolved in water? (a) \(\mathrm{NH}_{4} \mathrm{Cl}\) (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\) (butane) (c) \(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\) (table sugar) (d) \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}\)

Step-by-Step Solution

Answer

\( \mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2} \) conducts electricity when dissolved in water.

Step 1: Identify Ionic Compounds

To conduct electricity when dissolved, a substance must dissociate into ions in water. We need to identify which substances from the list are ionic compounds, as ionic compounds dissociate into ions in solution.

Step 2: Analyze \\( \mathrm{NH}_{4} \mathrm{Cl} \\\)

\( \mathrm{NH}_{4} \mathrm{Cl} \) is an ionic compound because it consists of \( \mathrm{NH}_{4}^{+} \) (ammonium ion) and \( \mathrm{Cl}^{-} \) (chloride ion). It dissociates into these ions when dissolved in water, allowing the solution to conduct electricity.

Step 3: Analyze \\( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3} \\\)

Butane \( ( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}) \) is a molecular compound with nonpolar covalent bonds; it does not dissociate into ions in water and, thus, does not conduct electricity.

Step 4: Analyze \\( \mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11} \\\)

Table sugar, or sucrose, \( \mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11} \), is a molecular compound. It does not dissociate into ions in water, so it cannot conduct electricity.

Step 5: Analyze \\( \mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2} \\\)

Barium nitrate, \( \mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2} \), is an ionic compound. It dissociates into \( \mathrm{Ba}^{2+} \) ions and \( \mathrm{NO}_{3}^{-} \) ions in water, allowing the solution to conduct electricity.

Step 6: Conclusion

Both \( \mathrm{NH}_{4} \mathrm{Cl} \) and \( \mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2} \) are ionic compounds that can conduct electricity when dissolved in water, but only one option needs to be chosen based on the typical format given for these questions.

Key Concepts

Electrical Conductivity in Solutions

When substances dissolve in water, they may or may not conduct electricity. This ability largely depends on whether the substance can dissociate into charged ions.

• Ionic Compounds: When dissolved, these compounds generally break into positive and negative ions. These free ions move in the liquid and carry electric current, making the solution conductive.
• Molecular Compounds: These tend to remain intact as molecules and do not form ions. As a result, they usually do not conduct electricity when dissolved in water.

Understanding the difference between these types of compounds is essential for predicting electrical conductivity. When you combine this with knowing the nature of a substance (ionic or molecular), you can determine if it will conduct electricity in a solution.

Ion Dissociation

Ion dissociation is a crucial process for electrical conductivity in solutions. It's the breaking apart of an ionic compound into its individual ions when introduced to a solvent like water.
For example, when ammonium chloride ( \( \mathrm{NH}_{4} \mathrm{Cl} \) ) is dissolved, it separates into ( \( \mathrm{NH}_4^+ \) ) and ( \( \mathrm{Cl}^- \) ) ions. These ions are responsible for conducting electricity as they move freely in the solution.

• Step-by-Step Dissociation: Initially, the solid ionic compound comes into contact with the solvent. The water molecules surround and pull apart the ions from the solid structure, allowing them to disperse throughout the solution.

This process is fundamental to the behavior of ionic compounds in water and their ability to facilitate electric current.

Molecular vs. Ionic Compounds

Distinguishing between molecular and ionic compounds helps in understanding their properties, including solubility and electrical conductivity.

• Ionic Compounds: These are formed by the electrostatic attraction between positively and negatively charged ions. They typically have high melting points and dissolve in water to produce ions, thus conducting electricity.
• Molecular Compounds: Made up of atoms held together by covalent bonds, they generally do not break into ions in water. An example is butane \( (\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}) \), a non-polar molecular compound that doesn't conduct electricity in a solution.

Understanding these differences is vital when predicting whether a substance will conduct electricity in a solution. Ionic compounds like ammonium chloride and barium nitrate can do this, while molecular compounds like butane and table sugar cannot.