Consider the titration of a 25.0-mL sample of 0.175 M CH₃NH₂ with 0.150 M HBr. Determine each quantity. c. the pH at 5.0 mL of added acid

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Identify the initial moles of CH_3NH_2 in the solution using the formula: \( \text{moles} = M \times V \).

Calculate the moles of HBr added using the formula: \( \text{moles} = M \times V \).

Determine the moles of CH_3NH_2 remaining after reaction with HBr by subtracting the moles of HBr from the initial moles of CH_3NH_2.

Calculate the concentration of CH_3NH_2 and CH_3NH_3^+ in the solution after the reaction, considering the total volume of the solution.

Use the Henderson-Hasselbalch equation to find the pH: \( \text{pH} = pK_a + \log \left( \frac{[\text{base}]}{[\text{acid}]} \right) \), where \( pK_a \) is derived from \( K_b \) of CH_3NH_2.

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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 (a solution of known concentration) to a sample until a reaction reaches its endpoint, often indicated by a color change. In this case, the titration involves a weak base (methylamine) being neutralized by a strong acid (HBr).

pH Calculation

pH is a measure of the acidity or basicity of a solution, calculated as the negative logarithm of the hydrogen ion concentration. In titrations, the pH can change significantly as the titrant is added, especially near the equivalence point. For weak bases like methylamine, the pH at various points can be calculated using the Henderson-Hasselbalch equation or by considering the dissociation of the weak base and the resulting conjugate acid.

Buffer Solutions

Buffer solutions are mixtures that resist changes in pH upon the addition of small amounts of acid or base. In the context of this titration, when a weak base is partially neutralized by a strong acid, a buffer system is formed, which can help maintain a relatively stable pH in the solution. Understanding how buffers work is crucial for predicting the pH at specific points during the titration.

Consider the titration of a 25.0-mL sample of 0.175 M CH3NH2 with 0.150 M HBr. Determine each quantity. c. the pH at 5.0 mL of added acid