Question

K, L and M are beakers containing three different solutions as shown below.

Name the beaker which:

1. contains only ions.
2. contains only molecules.
3. has pH less than 7.

Answer 1

1. Beaker L contains only ions. Sodium chloride solution (NaCl) is a strong electrolyte. When it dissolves in water, it dissociates completely into sodium ions (Na⁺) and chloride ions (Cl⁻). In basic chemistry classification, strong electrolytes are often described as containing “only ions” in solution (referring to the state of the solute), whereas the other substances have significant molecular components.
2. Beaker M contains only molecules. Distilled water consists of H₂O molecules. While a tiny fraction of water molecules naturally dissociate into ions, it is so negligible (10⁻⁷ moles per liter) that distilled water is considered to contain only molecules for the purposes of this classification.
3. Beaker K has a pH less than 7. Aqueous acetic acid (CH₃COOH) is an organic acid. Acids increase the concentration of hydrogen ions (H⁺) in a solution, resulting in a pH lower than 7.