Question

Which description is true of 0.02 M Ca(OH)2 if Ca(OH)2 completely dissociates in water? A. It’s a dilute strong acid. B. It’s a dilute strong base. C. It’s a dilute weak base. D. It’s a concentrated weak base. E. It’s a concentrated weak acid.

Answer 1

Answer: B. It’s a dilute strong base.

Explanation:

1) Definition of acids and bases: as per Bronsted-Lowry model, an acid is a substance that donates hydrogen ions and a base is a substance that accepts hydrogen ions.

Ca(OH)₂ does not have hydrogen ions to donate, but it can accept hydrogen ions to form H₂O according to this equation: H⁺ + OH⁻ → H₂O.

Hence,  Ca(OH)₂ is a base.

2) Definition of strong base: a strong base is a base that dissociates completely into metallic and hydroxide ions in aqueous solutions, while a weak base dissociates partially.

Hence, Ca(OH)₂ is a strong base.

3) Definition of dilute: it refers to a solution meaning that the substance is not pure and the concentration is low. Since, the solution the Ca(OH)₂ is 0.02 M means that it is dilute.

Therefore, we have found that the description of 0.02 M Ca(OH)₂ is that is is a dilute strong base (option B).