Predict whether the equivalence point of each of the following titrations is below, above, or at pH 7: (b) calcium hydroxide titrated with perchloric acid.

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Identify the nature of the titrant and the analyte. In this case, calcium hydroxide (Ca(OH)2) is a strong base and perchloric acid (HClO4) is a strong acid.

Understand that the equivalence point in a titration is where the amount of titrant added is stoichiometrically equivalent to the amount of analyte present. For strong acid-strong base titrations, the reaction is a neutralization reaction.

Write the balanced chemical equation for the reaction: \( Ca(OH)_2 + 2HClO_4 \rightarrow Ca(ClO_4)_2 + 2H_2O \).

Recognize that at the equivalence point of a strong acid-strong base titration, the only species present in significant amounts are the salt and water. The salt formed does not undergo any hydrolysis as it is a neutral salt.

Conclude that since the salt formed does not affect the pH and water is neutral, the pH at the equivalence point will be at pH 7.

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주요 개념

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Strong Acid-Strong Base Titration

In a strong acid-strong base titration, the equivalence point occurs when the amount of acid equals the amount of base, resulting in a neutral solution. For titrations involving strong acids like perchloric acid and strong bases like calcium hydroxide, the pH at the equivalence point is typically around 7, indicating neutrality.

pH of Calcium Hydroxide

Calcium hydroxide (Ca(OH)₂) is a strong base that dissociates completely in water to produce hydroxide ions (OH⁻). This results in a high pH solution, typically above 12. When titrated with a strong acid, the initial pH is significantly higher than 7, influencing the pH at the equivalence point.

Effect of Strong Acid on pH

When a strong acid like perchloric acid is added to a strong base, the resulting solution's pH at the equivalence point depends on the relative strengths of the acid and base. In this case, since both are strong, the pH at the equivalence point will be neutral (around 7), but the initial high pH of the base means the transition will be significant, leading to a final pH that may be slightly below 7 due to the excess of H⁺ ions.