Question

State whether each of the following statements is true or false. Justify your answer in each case. \begin{equation} \begin{array}{l}{\text { (a) When methanol, } \mathrm{CH}_{3} \mathrm{OH}, \text { is dissolved in water, a con- }} \\ {\text { ducting solution results. }} \\ {\text { (b) When acetic acid, } \mathrm{CH}_{3} \mathrm{COOH} \text { , dissolves in water, the }} \\ {\text { solution is weakly conducting and acidic in nature. }}\end{array} \end{equation}

Short answer

(a) False. Methanol (CH3OH) doesn't dissociate into ions when dissolved in water and thus doesn't produce a conducting solution. (b) True. Acetic acid (CH3COOH) forms a weakly conducting and acidic solution when dissolved in water due to partial ionization into acetate ions (CH3COO-) and hydrogen ions (H+).

Step-by-step solution

Statement (a) analysis and justification

Methanol has a molecular formula of CH3OH and is a polar organic molecule. When methanol is dissolved in water, it forms a homogeneous mixture due to its polar nature. The OH in methanol can hydrogen bond with the water molecules. However, methanol doesn't dissociate into charged ions when dissolved in water. As a result, it doesn't produce ions that can facilitate the flow of electricity. Since the conductivity of a solution depends on the movement of ions, methanol in water doesn't result in a conducting solution. Therefore, the statement (a) is false.

Statement (b) analysis and justification

Acetic acid has the molecular formula CH3COOH. When acetic acid dissolves in water, it undergoes ionization to form acetate ions (CH3COO-) and hydrogen ions (H+). However, acetic acid is a weak acid, which means it doesn't ionize completely in water. A small fraction of the acetic acid molecules ionize, releasing a small concentration of H+ ions into the solution. The presence of H+ ions makes the solution acidic. As a weak electrolyte, the solution formed by dissolving acetic acid in water is weakly conducting. The low concentration of ions (CH3COO- and H+) in the solution is responsible for its weak conductivity. So, the statement (b) is true that when acetic acid dissolves in water, the solution is weakly conducting and acidic in nature.

Key concepts

Electrolytes and Conductivity

Understanding how substances can affect the electrical conductivity of solutions is fundamental in chemistry. Electrolytes are substances that dissolve in water to produce a solution that conducts electricity. This is because they separate into ions, which are charged particles. The movement of these ions allows electrical currents to pass through the solution.

Ions come in two varieties: cations, which carry a positive charge, and anions, which are negatively charged. The greater the concentration of ions in a solution, the better it conducts electricity. Electrolytes can be classified as strong or weak, depending on their ability to ionize. Strong electrolytes, such as table salt (sodium chloride), dissociate completely in water, while weak electrolytes, like acetic acid, only partially dissociate.

Non-electrolytes, on the other hand, do not produce ions in solution, failing to conduct electricity. Examples include sugar and methanol that, although they dissolve in water, do not separate into ions.

Properties of Methanol in Water

Methanol (CH₃OH) is an organic compound with properties that influence how it behaves when dissolved in water. Due to its polar nature, methanol mixes readily with water, creating what's known as a homogeneous solution. This means that the methanol molecules are evenly distributed throughout the water.

One of the distinctive properties of methanol in water is its ability to form hydrogen bonds with water molecules. These bonds occur because the oxygen atom in methanol has a slight negative charge, which attracts the slightly positive hydrogen atoms of water. However, it is crucial to note that while methanol engages in hydrogen bonding, it does not ionize to form free ions in the solution. Therefore, even though methanol interacts well with water, it does not contribute to the solution's conductivity.

Ionization of Acetic Acid

When exploring the ionization of acetic acid (CH₃COOH) in water, we delve into the process by which acetic acid molecules separate into ions. Upon dissolving, acetic acid partially ionizes to produce acetate ions (CH₃COO^-) and hydrogen ions (H⁺). It is the hydrogen ions, in particular, that are responsible for the acidic nature of the resulting solution.

The term 'partial ionization' is key here; acetic acid is a weak acid, meaning not all of its molecules will ionize at the same time. The degree to which acetic acid ionizes is governed by its acid dissociation constant (Ka), which quantifies its strength as an acid. The equilibrium between undissociated acetic acid and its ions in solution is delicate and easily disturbed by changes in concentration or the addition of other substances.

Acidic Solutions and Acidity

The concept of acidity in solutions is predominantly tied to the presence of hydrogen ions (H⁺). An acidic solution has an excess of these ions, which is often a result of acids dissolving in water. pH is the scale used to measure the acidity of a solution; the lower the pH, the more acidic the solution is.

Substances that release more hydrogen ions increase the acidity, while those that reduce the concentration of hydrogen ions (like bases) make the solution less acidic. Weak acids, such as acetic acid, contribute to acidity but not to the extent of strong acids, which fully dissociate and release a higher concentration of hydrogen ions. The acidity of a solution affects a myriad of chemical properties and reactions, including the behavior of enzymes, the solubility of minerals, and the corrosiveness of a liquid.