Problem 14 - Chemistry: The Central Science

Question

State whether each of the statements below is true or false. Justify your answer in each case. (a) When methanol, \(\mathrm{CH}_{3} \mathrm{OH}\), is dissolved in water, a conducting solution results. (b) When acetic acid, \(\mathrm{CH}_{3} \mathrm{COOH}_{\text {, dissolves in water, the so- }}^{\text {- }}\) lution is weakly conducting and acidic in nature.

Step-by-Step Solution

Answer

(a) False. When methanol (\(\mathrm{CH}_{3} \mathrm{OH}\)) is dissolved in water, a non-conducting solution results, as methanol does not dissociate into ions. (b) True. When acetic acid (\(\mathrm{CH}_{3} \mathrm{COOH}\)) dissolves in water, the solution is weakly conducting and acidic in nature due to the partial ionization of the acid.

Step 1: (a) Methanol in water – Analyzing conductivity

Methanol (\(\text{CH}_3\text{OH}\)) is a covalent compound composed of hydrogen, carbon, and oxygen atoms. When it is dissolved in water, it forms hydrogen bonds with water molecules, but it does not dissociate into ionized particles. A conducting solution is formed mainly due to the presence of free ions in the solution. Since methanol is non-electrolyte, it does not produce ions in an aqueous solution. Therefore, the dissolved methanol's solution in water is non-conducting.

Step 2: (a) Methanol: True or False

The statement is False. When methanol (\(\mathrm{CH}_{3} \mathrm{OH}\)) is dissolved in water, a non-conducting solution results, as methanol does not dissociate into ions.

Step 3: (b) Acetic acid in water – Analyzing conductivity and acidity

Acetic acid (\(\mathrm{CH}_{3} \mathrm{COOH}\)) is a weak acid. When acetic acid is dissolved in water, it undergoes a partial ionization, which means some of the acetic acid molecules dissociate into ions (\(\mathrm{CH}_{3} \mathrm{COO}^{-}\) and \(H^{+}\)). The presence of these ions in the solution allows electric current to flow, making the solution weakly conducting. Additionally, excess \(H^{+}\) ions give the solution its acidic nature. The acidic reaction can be represented as: \(\mathrm{CH}_{3} \mathrm{COOH}\) \(\text{(aq)} + \text{H}_2\text{O}\) \(\text{(l)} \,\rightleftharpoons\,\) \(\mathrm{CH}_{3} \mathrm{COO}^{-}\) \(\text{(aq)} + \text{H}_3\text{O}^{+}\) \(\text{(aq)}\)

Step 4: (b) Acetic acid: True or False

The statement is True. When acetic acid (\(\mathrm{CH}_{3} \mathrm{COOH}\)) dissolves in water, the solution is weakly conducting and acidic in nature due to the partial ionization of the acid.

Key Concepts

Methanol

Methanol is a simple alcohol with the chemical formula \( ext{CH}_3 ext{OH}\). It is a covalent compound, meaning that its atoms are bonded together by sharing electrons. This structure is key to understanding its behavior in water.When methanol is mixed with water, it forms hydrogen bonds, but it doesn't break into ions. This union is purely physical, not chemical. Since methanol doesn't create charged particles, it doesn't conduct electricity. For a solution to be conductive, it must contain ions, which are absent in a methanol-water solution. Thus, methanol remains non-conducting when it dissolves in water. Remember, only solutions with free-moving ions can conduct electricity efficiently.

Acetic Acid

Acetic acid, also known as \( ext{CH}_3 ext{COOH}\), is a weak acid commonly found in vinegar. When it dissolves in water, it partially dissociates into ions. This means that only some of the acetic acid molecules break into \( ext{CH}_3 ext{COO}^-\) and \(H^+\) ions.

• These ions can carry an electric charge, enabling the solution to conduct electricity.
• The degree of ionization is not complete, leading to weak conductivity as opposed to strong acids which fully ionize.

This partial ionization also lends the solution its acidic properties. Acetic acid solutions are thus both weakly conducting and acidic.

Ionization

Ionization is the process where molecules split into ions in a solution. This is a crucial concept because only ions allow the solution to conduct electricity.

• Unlike strong acids or bases, weak acids like acetic acid only partially ionize. This means fewer ions are formed.
• The degree of ionization impacts the overall conductivity of the solution.

Ionization is reversible, as depicted by the equilibrium reaction: \[ ext{CH}_3 ext{COOH (aq)} + ext{H}_2 ext{O (l)} ightleftharpoons ext{CH}_3 ext{COO}^- ext{(aq)} + ext{H}_3 ext{O}^+ ext{(aq)}\] The reversible nature signifies the balance between undissociated molecules and ions.

Weak Electrolyte

Weak electrolytes are substances that only partially ionize in solution. This category includes weak acids and bases like acetic acid. When dissolved in water, they produce a limited amount of ions, resulting in low electrical conductivity.

• They contrast with strong electrolytes, which ionize completely, producing numerous ions and exhibiting strong conductivity.
• Understanding the degree of ionization helps explain why weak electrolytes can't conduct electricity well.

Acetic acid is a perfect example, where it only partially breaks into ions, illustrating the concept of weak electrolytes. The ability of a solution to conduct electricity depends significantly on its ion content.