Equilibrium

Question 1

Similarity within a Group or Period

Answer 1

Elements in the same group possess identical valence‑electron counts, so they form ions of the same charge and display comparable chemical behaviour. Elements in the same period have the same number of electron shells but varying valence structures, giving a gradual shift from metallic to non‑metallic properties across the row. Thus group membership predicts reactivity, while period membership indicates energy level.

Question 2

Acid‑Base Conjugate Pairs

Answer 2

When an acid loses a proton it becomes its conjugate base, whereas when a base gains a proton it forms its conjugate acid. The pair differs by a single H⁺ and exists on opposite sides of a reversible proton‑transfer equilibrium. Their strengths are inversely related: a strong acid pairs with a weak conjugate base.

Question 3

Calculating K₍a₎ or K₍b₎

Answer 3

For a weak acid write HA ⇌ H⁺ + A⁻, set up an ICE table, measure the equilibrium pH to obtain [H⁺], and substitute into K₍a₎ = [H⁺][A⁻]/[HA]. The same logic with OH⁻ yields K₍b₎ for bases. These constants measure intrinsic acid or base strength.