Question

which of the following would most effectively resist a ph change when small amounts of acid or base are added?
vinegar
saline solution
water
buffer solution

which substance is likely to have a ph close to 7?
blood
orange juice
vinegar
ammonia

Explanation:

• First question: A buffer solution is designed to resist pH changes. It contains a weak acid and its conjugate base (or vice - versa). When small amounts of acid are added, the conjugate base reacts with the added \(H^{+}\) ions. When small amounts of base are added, the weak acid reacts with the added \(OH^{-}\) ions. Vinegar is an acid (\(CH_{3}COOH\)), saline solution (\(NaCl\) in water) and water (\(H_{2}O\)) do not have the acid - base pair to resist pH changes like a buffer.
• Second question: Blood has a pH range of approximately 7.35 - 7.45. Orange juice contains citric acid (\(pH\approx 3\)), vinegar is acetic acid (\(pH\approx 2.5 - 3\)), and ammonia (\(NH_{3}\)) is a base (\(pH > 7\)).

Answer:

• First question: Buffer solution
• Second question: Blood