A Level Chemistry OCR Practice Exam

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Prepare for the A Level Chemistry OCR Exam with quizzes. Study with flashcards, multiple choice questions, hints, and explanations. Enhance your understanding and boost your confidence for success!

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Which substance is considered a strong acid?

Water
Sodium chloride
Hydrochloric acid
Ammonia

The correct answer is: Hydrochloric acid

Hydrochloric acid is considered a strong acid because it completely dissociates in water to produce hydrogen ions (H⁺) and chloride ions (Cl⁻). This complete ionization means that solutions of hydrochloric acid have a high concentration of H⁺ ions, which is characteristic of strong acids. Strong acids are known for their ability to significantly lower the pH of a solution and can react vigorously with bases or other substances. In contrast, water is a neutral substance that does not exhibit acidic properties; sodium chloride is a neutral salt formed from a strong acid (HCl) and a strong base (NaOH), and it does not contribute H⁺ ions in solution. Ammonia is a weak base that does not dissociate to produce a significant amount of H⁺ ions. Thus, hydrochloric acid stands out as the strong acid among the choices presented.