Distinguish between a strong acid and a weak acid with one example each.

Distinguish between a strong acid and a weak acid with one example each.

• A. A strong acid fully dissociates in water (e.g., HCl).
• B. A strong acid partially dissociates in water (e.g., CH3COOH).
• C. A weak acid fully dissociates in water (e.g., H2SO4).
• D. A weak acid does not ionize in water (e.g., HCN).

Answer: (A)

Strong acids and weak acids differ by how completely they ionize in water. A strong acid like hydrochloric acid dissociates fully in aqueous solution: HCl splits into H3O+ and Cl-, so essentially every molecule donates its proton. This full ionization is why such solutions conduct electricity well and have very low pH values. A weak acid, such as acetic acid, only partially dissociates: CH3COOH ⇌ H3O+ + CH3COO−, so most of the molecules remain undissociated and the [H3O+] is much smaller, giving a higher pH at the same concentration. The extent of dissociation is described by the acid dissociation constant Ka; large Ka corresponds to strong acids (near-complete ionization in water) and small Ka to weak acids. Thus, describing a strong acid as fully dissociating in water with HCl as an example is the best match. The other statements misstate the behavior—strong acids do not partially dissociate, and weak acids do ionize to some extent (they do not remain completely undissociated).

Strong acids and weak acids differ by how completely they ionize in water. A strong acid like hydrochloric acid dissociates fully in aqueous solution: HCl splits into H3O+ and Cl-, so essentially every molecule donates its proton. This full ionization is why such solutions conduct electricity well and have very low pH values. A weak acid, such as acetic acid, only partially dissociates: CH3COOH ⇌ H3O+ + CH3COO−, so most of the molecules remain undissociated and the [H3O+] is much smaller, giving a higher pH at the same concentration. The extent of dissociation is described by the acid dissociation constant Ka; large Ka corresponds to strong acids (near-complete ionization in water) and small Ka to weak acids.

Thus, describing a strong acid as fully dissociating in water with HCl as an example is the best match. The other statements misstate the behavior—strong acids do not partially dissociate, and weak acids do ionize to some extent (they do not remain completely undissociated).