Problem 33 - Chemistry The Central Science

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) Sulfuric acid is a monoprotic acid. }} \\ {\text { (b) HCl is a weak acid. }} \\ {\text { (c) Methanol is a base. }}\end{array} \end{equation}

Step-by-Step Solution

Answer

(a) FALSE. Sulfuric acid (H₂SO₄) is a diprotic acid, not a monoprotic acid, as it can donate two protons per molecule. (b) FALSE. HCl is a strong acid, not a weak acid, as it dissociates completely in water. (c) FALSE. Methanol (CH3OH) does not typically exhibit basic properties. Instead, it can act as a weak acid by donating a proton from its hydroxyl group.

Step 1: (a) Determine the nature of sulfuric acid

Sulfuric acid (H₂SO₄) is an acid, so we need to determine if it is monoprotic or not. A monoprotic acid is one that can donate only one proton (H⁺) per molecule. Looking at the chemical formula of sulfuric acid (H₂SO₄), we can see that it contains two hydrogen atoms. This means sulfuric acid can donate two protons per molecule. Therefore, it should be classified as a diprotic acid. So the statement (a) "Sulfuric acid is a monoprotic acid" is FALSE.

Step 2: (b) Determine the acidity of HCl

HCl (hydrochloric acid) is an acid. We need to decide on its strength – whether it is a weak acid or a strong acid. The strength of an acid is determined by how much it dissociates in water. Strong acids dissociate completely in water, while weak acids dissociate only partially. HCl, when dissolved in water, completely dissociates into H⁺ and Cl⁻ ions. \( HCl (aq) \rightarrow H^+ (aq) + Cl^-(aq) \) Since HCl dissociates completely, it is considered a strong acid, not a weak acid. So the statement (b) "HCl is a weak acid" is FALSE.

Step 3: (c) Determine if methanol is a base

Methanol (CH3OH) is an organic compound and belongs to the group of alcohols. We need to examine if it exhibits basic properties or not. A base typically accepts protons (H⁺) in a chemical reaction. Methanol does not typically accept protons in its reactions. Instead, it can act as a weak acid by donating a proton (H⁺) from its hydroxyl group (OH). \( CH3OH \leftrightharpoons H^+ (aq) + CH3O^- (aq) \) So the statement (c) "Methanol is a base" is FALSE.

Key Concepts

Sulfuric Acid

Sulfuric acid, with the chemical formula \(H_2SO_4\), is one of the most important industrial chemicals. It's often used in the production of fertilizers, in petroleum refining, and even in wastewater processing.
As a strong acid, sulfuric acid fully dissociates in water, releasing hydrogen ions (protons) and forming sulfate ions. This characteristic makes it highly reactive and potent as an acid.
Despite its strength, one of the unique features of sulfuric acid is its diprotic nature. It means it can donate two protons or hydrogen ions per molecule in two steps. In the first step, it donates one proton to form the bisulfate ion \(HSO_4^-\):

• First ionization: \(H_2SO_4 \rightarrow H^+ + HSO_4^-\)
• Second ionization: \(HSO_4^- \rightarrow H^+ + SO_4^{2-}\)

Understanding this property helps in differentiating sulfuric acid from monoprotic acids, which can donate only one proton, thus simplifying many students' grasp of acid-base chemistry.

Monoprotic vs Diprotic Acids

Acids can be classified based on the number of protons they can donate. Monoprotic acids, like hydrochloric acid \(HCl\), donate one proton per molecule in aqueous solutions. These acids are straightforward in their reactions:
For instance, with \(HCl\), the dissociation in water is simple:

• \(HCl \rightarrow H^+ + Cl^-\)

On the other hand, diprotic acids, such as sulfuric acid \(H_2SO_4\), can donate two protons. This means they have two stages of dissociation. The first dissociation happens more easily compared to the second.
This distinction is vital because it affects the calculations and predictions in chemistry involving pH, acid strength, and titration processes.

Strong and Weak Acids

Understanding the difference between strong and weak acids is fundamental in acid-base chemistry.
Strong acids, like hydrochloric acid \(HCl\), dissociate completely in water, meaning they release all their hydrogen ions and leave no undissociated acid in the solution. This full dissociation results in a higher concentration of hydrogen ions and consequently, a lower pH.
In contrast, weak acids only partially dissociate. This means not all the acid molecules donate their protons in solution, leading to less hydrogen ion concentration and a higher pH compared to strong acids. Examples of weak acids include acetic acid \(CH_3COOH\) and formic acid \(HCOOH\).
Recognizing whether an acid is strong or weak is useful in predicting the chemical behavior and reactivity of the acid in various contexts.

Methanol as an Alcohol

Methanol \((CH_3OH)\) is an alcohol, which is an organic compound containing one or more hydroxyl \((OH)\) groups.
Alcohols do not behave like traditional bases. Instead, they feature acid-like properties, albeit weak. Methanol, for instance, can slightly donate a proton from its hydroxyl group, acting as a weak acid:
\(CH_3OH \leftrightharpoons H^+ + CH_3O^-\)
However, this does not make it a base. Unlike bases, methanol doesn't accept protons (\(H^+\)) or form \(OH^-\) ions readily in solution.
Understanding methanol in this context is important, especially when differentiating between alcohols and bases in organic chemistry. It is more accurate to consider its role and reactivity due to its weak acidity rather than any basic characteristics.