Textbook Question
Consider the titration curves (labeled a and b) for two weak bases, both titrated with 0.100 M HCl. (a)
(b)
(ii) Which base has the larger Kb?
Ch.18 - Aqueous Ionic Equilibrium
Chapter 18, Problem 85
A 20.0-mL sample of 0.115 M sulfurous acid (H2SO3) solution is titrated with 0.1014 M KOH. At what added volume of base solution does each equivalence point occur?
Verified step by step guidance1
Identify the reaction: Sulfurous acid (H2SO3) is a diprotic acid, meaning it can donate two protons (H+). The reaction with KOH, a strong base, occurs in two steps: H2SO3 + KOH -> KHSO3 + H2O and KHSO3 + KOH -> K2SO3 + H2O.
Calculate the moles of H2SO3: Use the concentration and volume of the sulfurous acid solution to find the initial moles of H2SO3. Moles of H2SO3 = 0.115 M * 0.020 L.
Determine the moles of KOH needed for the first equivalence point: At the first equivalence point, all H2SO3 is converted to KHSO3. This requires an equal number of moles of KOH as there are moles of H2SO3.
Calculate the volume of KOH for the first equivalence point: Use the moles of KOH needed and the concentration of the KOH solution to find the volume. Volume (L) = moles of KOH / 0.1014 M.
Determine the volume of KOH for the second equivalence point: At the second equivalence point, all KHSO3 is converted to K2SO3. This requires an additional equal number of moles of KOH as the initial moles of H2SO3. Calculate the total volume of KOH needed for both equivalence points.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
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, KOH) to a solution of the analyte (H2SO3) until the reaction reaches its equivalence point, where stoichiometrically equivalent amounts of acid and base have reacted.
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03:04
Acid-Base Titration
Equivalence Point
The equivalence point in a titration is the stage at which the amount of titrant added is exactly enough to completely neutralize the analyte solution. For a diprotic acid like sulfurous acid, there are two equivalence points corresponding to the neutralization of each acidic proton, which must be calculated based on the stoichiometry of the reaction.
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01:07At the Equivalence Point
Molarity and Volume Relationship
Molarity (M) is defined as the number of moles of solute per liter of solution. In titration calculations, the relationship between the molarity and volume of the acid and base solutions is crucial. The formula M1V1 = M2V2 allows us to determine the volume of titrant needed to reach the equivalence point, where M1 and V1 are the molarity and volume of the acid, and M2 and V2 are those of the base.
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Related Practice
Textbook Question
A 0.229-g sample of an unknown monoprotic acid is titrated with 0.112 M NaOH. The resulting titration curve is shown here. Determine the molar mass and pKa of the acid.
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Textbook Question
Methyl red has a pKa of 5.0 and is red in its acid form and yellow in its basic form. If several drops of this indicator are placed in a 25.0-mL sample of 0.100 M HCl, what color will the solution appear? If 0.100 M NaOH is slowly added to the HCl sample, in what pH range will the indicator change color?
Textbook Question
Referring to Table 18.1, pick an indicator for use in the titration of each acid with a strong base. a. HF