A 20.0-mL sample of 0.150 M KOH is titrated with 0.125 M HClO₄ solution. Calculate the pH after the following volumes of acid have been added: (d) 25.0 mL. (e) 30.0 mL.

검증된 단계별 안내

Step 1: Begin by calculating the initial moles of KOH in the 20.0 mL sample. Use the formula: \( \text{moles} = \text{volume (L)} \times \text{molarity (M)} \). Convert 20.0 mL to liters by dividing by 1000.

Step 2: Calculate the moles of HClO4 added for each volume (25.0 mL and 30.0 mL). Use the same formula: \( \text{moles} = \text{volume (L)} \times \text{molarity (M)} \). Convert the volumes from mL to liters.

Step 3: Determine the reaction between KOH and HClO4. The balanced chemical equation is: \( \text{KOH} + \text{HClO4} \rightarrow \text{KClO4} + \text{H2O} \). This is a 1:1 reaction, meaning one mole of KOH reacts with one mole of HClO4.

Step 4: For each volume of HClO4 added, calculate the remaining moles of KOH or HClO4 after the reaction. Subtract the moles of HClO4 from the initial moles of KOH to find the excess reactant.

Step 5: Calculate the pH based on the excess reactant. If KOH is in excess, calculate the concentration of OH⁻ ions and use \( \text{pOH} = -\log[\text{OH}^-] \) to find pH. If HClO4 is in excess, calculate the concentration of H⁺ ions and use \( \text{pH} = -\log[\text{H}^+] \).

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Titration

Titration is a quantitative analytical technique used to determine the concentration of a solute in a solution. It involves the gradual addition of a titrant (in this case, HClO4) to a solution of the analyte (KOH) until the reaction reaches its equivalence point, where the amount of titrant added is stoichiometrically equivalent to the amount of analyte present.

pH Calculation

pH is a measure of the acidity or basicity of a solution, defined as the negative logarithm of the hydrogen ion concentration. In titration problems, pH can be calculated at various points by considering the concentrations of the remaining acid or base after neutralization, as well as the resulting solution's characteristics, such as whether it is acidic, basic, or neutral.

Neutralization Reaction

A neutralization reaction occurs when an acid reacts with a base to produce water and a salt. In this scenario, KOH (a strong base) reacts with HClO4 (a strong acid) to form water and potassium perchlorate. Understanding the stoichiometry of this reaction is crucial for determining the amounts of reactants and products at different stages of the titration.

A 20.0-mL sample of 0.150 M KOH is titrated with 0.125 M HClO4 solution. Calculate the pH after the following volumes of acid have been added: (d) 25.0 mL. (e) 30.0 mL.