Problem 14 - Chemistry: The Central Science in SI Units, Global Edition

Question

State whether each of the following statements is true or false. Justify your answer in each case. (a) When acetone, \(\mathrm{CH}_{3} \mathrm{COCH}_{3}\), is dissolved in water, a conducting solution results. (b) When ammonium nitrate, \(\mathrm{NH}_{4} \mathrm{NO}_{3}\), dissolves in water, the solution is weakly conducting and basic in nature.

Step-by-Step Solution

Answer

(a) False - Acetone is a covalent compound and does not dissociate into ions when dissolved in water; thus, it cannot produce a conducting solution. (b) False - Ammonium nitrate dissociates into ions in water, resulting in a weakly conducting solution; however, it is acidic in nature due to the presence of hydronium ions, not basic.

Step 1: (a) Determine properties of acetone solution

Acetone, \(\mathrm{CH}_{3} \mathrm{COCH}_{3}\), is a covalent compound; formed by the sharing of electrons between non-metal atoms (carbon, hydrogen, and oxygen). When dissolved in water, it forms a homogenous mixture also known as a solution, but it does not dissociate into ions. Electrolytes are substances that, when dissolved in water, dissociate into ions and become capable of conducting an electric current. Since acetone does not dissociate into ions in water, it cannot produce a conducting solution. The statement is: \(False\)

Step 2: (b) Determine properties of ammonium nitrate solution

Ammonium nitrate, \(\mathrm{NH}_{4} \mathrm{NO}_{3}\), is a salt formed from the reaction between a weak base (ammonium hydroxide, \(\mathrm{NH}_{4}\mathrm{OH}\)) and a strong acid (nitric acid: \(\mathrm{NO}_{3}\)). When dissolved in water, it completely dissociates into its constituent ions, \(\mathrm{NH}_{4}^{+}\) (ammonium) and \(\mathrm{NO}_{3}^{-}\) (nitrate). Since it dissociates into ions, the solution of ammonium nitrate in water is capable of conducting electricity, making it a weakly conducting solution as stated in the problem. Now we need to determine the nature of the solution (whether it is acidic or basic). As mentioned earlier, ammonium nitrate is a salt of a weak base and a strong acid. In water, the ammonium ion (\(\mathrm{NH}_{4}^{+}\)) can donate a proton (\(\mathrm{H}^{+}\)) to water molecules, forming \(\mathrm{NH}_{3}\) (ammonia) and \(\mathrm{H}_{3}\mathrm{O}^{+}\) (hydronium ion). On the other hand, nitrate ion (\(\mathrm{NO}_{3}^{-}\)) does not associate with water and doesn't influence the pH. Since the solution contains \(\mathrm{H}_{3}\mathrm{O}^{+}\) ions, it has a pH below 7, meaning it should be acidic, not basic, in nature. The statement is: \(False\) In summary, both statements (a) and (b) are false. Acetone does not form a conducting solution when dissolved in water, and a solution of ammonium nitrate in water is weakly conducting and acidic in nature, not basic.

Key Concepts

Covalent Compounds

Covalent compounds are fascinating chemical structures where atoms share electron pairs to form a molecule. This sharing often involves non-metals, creating a stable connection without any ions moving independently. Therefore, covalent compounds are quite different from ionic compounds, which consist of charged ions.

• Examples include water (H₂O), carbon dioxide (CO₂), and methane (CH₄).
• They are known for having relatively low melting and boiling points compared to ionic compounds.
• Covalent bonds can be polar or nonpolar, depending on the electronegativity difference between the bonded atoms.

An important characteristic of covalent compounds, such as acetone, is that they do not dissociate into ions when dissolved in water. This means they do not conduct electricity, as there are no charged particles to facilitate an electric current. In the context of acetone, it simply forms a homogenous mixture with water, without breaking down into ions.

Aqueous Solutions

An aqueous solution is a solution where water acts as the solvent. This type of solution is integral in both chemistry and biology due to the exceptional properties of water.

• Water is often called the universal solvent as it can dissolve more substances than any other liquid.
• Aqueous solutions can conduct electricity if they contain free ions, known as electrolytes.

When substances like ammonium nitrate dissolve in water, they separate into ions, creating an ion-rich solution. This ability to dissociate into ions makes such solutions capable of conducting electricity, showing their status as electrolytes. In contrast, covalent compounds that do not dissociate, like sugar or acetone, remain non-conductive in their aqueous forms.

pH of Solutions

The pH of a solution is a measure of its acidity or basicity, scaled between 0 and 14. A solution with a pH less than 7 is considered acidic, while a solution with a pH greater than 7 is considered basic or alkaline.

• A pH of 7 is neutral, which is the pH of pure water.
• The pH scale is logarithmic, meaning each unit change represents a tenfold change in acidity or basicity.

In the case of ammonium nitrate, when it dissolves in water, it dissociates into ammonium and nitrate ions. The ammonium ion (\(\mathrm{NH}_4^+\)) releases a proton (\(\mathrm{H}^+\)), creating hydronium ions (\(\mathrm{H}_3\mathrm{O}^+\)), which results in an acidic solution with a pH below 7. This characteristic is crucial to understand the nature of electrolyte and buffer solutions in chemical reactions and processes.