Textbook Question
A 5.55-g sample of a weak acid with Ka = 1.3⨉10-4 was combined with 5.00 mL of 6.00 M NaOH, and the resulting solution was diluted to 750.0 mL. The measured pH of the solution was 4.25. What is the molar mass of the weak acid?
Ch.17 - Aqueous Ionic Equilibrium
Chapter 17, Problem 124
Calculate the pH at the beginning of the titration, at the equivalence point, at one-half of the equivalence point, and at 5.0 mL beyond the equivalence point to sketch the titration curve from Problem 123. Then, choose a suitable indicator for this titration from Table 17.1.
Verified step by step guidance1
insert step 1: Identify the type of titration involved, such as strong acid-strong base, weak acid-strong base, or weak base-strong acid. This will help determine the pH calculations at different points.
insert step 2: Calculate the initial pH before any titrant is added. For a weak acid or base, use the initial concentration and the appropriate equilibrium expression to find the pH.
insert step 3: Determine the pH at the equivalence point. For a strong acid-strong base titration, the pH will be neutral (pH = 7). For a weak acid-strong base titration, calculate the pH using the conjugate base formed at the equivalence point.
insert step 4: Calculate the pH at one-half of the equivalence point. For a weak acid-strong base titration, this is where the pH equals the pKa of the weak acid.
insert step 5: Calculate the pH 5.0 mL beyond the equivalence point by determining the concentration of excess titrant and using it to find the pH. Then, choose an indicator whose pH range includes the pH at the equivalence point.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
pH and its Calculation
pH is a measure of the hydrogen ion concentration in a solution, indicating its acidity or basicity. It is calculated using the formula pH = -log[H+]. Understanding how to calculate pH at different stages of a titration is crucial, as it helps determine the solution's behavior and the appropriate indicators to use.
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pH Calculation Example
Titration and Equivalence Point
Titration is a quantitative analytical method used to determine the concentration of a solute in a solution. The equivalence point is reached when the amount of titrant added is stoichiometrically equivalent to the amount of substance in the sample. Recognizing the significance of the equivalence point is essential for understanding the changes in pH during the titration process.
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03:06Equivalence Point in Titration
Indicators in Titration
Indicators are substances that change color at a specific pH range, signaling the endpoint of a titration. Choosing a suitable indicator depends on the pH at the equivalence point of the titration; it should change color close to this pH to provide an accurate visual cue. Familiarity with common indicators and their pH ranges is vital for effective titration analysis.
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Related Practice
Textbook Question
Pseudogout, a condition with symptoms similar to those of gout (see Problem 126), is caused by the formation of calcium diphosphate (Ca2P2O7) crystals within tendons, cartilage, and ligaments. Calcium diphosphate will precipitate out of blood plasma when diphosphate levels become abnormally high. If the calcium concentration in blood plasma is 9.2 mg/dL, and Ksp for calcium diphosphate is 8.64⨉10-13, what minimum concentration of diphosphate results in precipitation?