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Ch.17 - Additional Aspects of Aqueous Equilibria
Brown - Chemistry: The Central Science 14th Edition
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoBrown 14th EditionCh.17 - Additional Aspects of Aqueous EquilibriaProblema 91a
Capitolo 17, Problema 91a

A sample of 0.1687 g of an unknown monoprotic acid was dissolved in 25.0 mL of water and titrated with 0.1150 M NaOH. The acid required 15.5 mL of base to reach the equivalence point. (a) What is the molar mass of the acid?

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Start by understanding that the equivalence point in a titration is reached when the moles of acid equal the moles of base added. Since the acid is monoprotic, it donates one proton per molecule.
Calculate the moles of NaOH used in the titration. Use the formula: \( \text{moles of NaOH} = \text{volume (L)} \times \text{molarity (M)} \). Convert 15.5 mL to liters by dividing by 1000.
Since the moles of NaOH equal the moles of the unknown acid at the equivalence point, the moles of the acid are the same as the moles of NaOH calculated in the previous step.
Determine the molar mass of the acid using the formula: \( \text{molar mass} = \frac{\text{mass of acid (g)}}{\text{moles of acid}} \). Use the mass of the acid given (0.1687 g) and the moles of acid calculated.
Ensure all units are consistent and check your calculations for accuracy. The molar mass will be in units of g/mol.

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Monoprotic Acid

A monoprotic acid is an acid that can donate only one proton (H⁺ ion) per molecule during a chemical reaction. This characteristic simplifies titration calculations, as the amount of base required to neutralize the acid directly relates to the number of moles of the acid present in the solution.
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Binary Acids

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 being titrated, indicating that the acid has been completely neutralized by the base.
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Equivalence Point in Titration

Molar Mass Calculation

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). To calculate the molar mass of the unknown acid, one must first determine the number of moles of acid neutralized at the equivalence point using the volume and concentration of the titrant, and then relate this to the mass of the acid sample.
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Molar Mass Calculation Example
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Domanda del libro di testo

A sample of 0.1687 g of an unknown monoprotic acid was dissolved in 25.0 mL of water and titrated with 0.1150 M NaOH. The acid required 15.5 mL of base to reach the equivalence point. (b) After 7.25 mL of base had been added in the titration, the pH was found to be 2.85. What is the Ka for the unknown acid?

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A sample of 0.2140 g of an unknown monoprotic acid was dissolved in 25.0 mL of water and titrated with 0.0950 M NaOH. The acid required 30.0 mL of base to reach the equivalence point. (a) What is the molar mass of the acid?

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Mathematically prove that the pH at the halfway point of a titration of a weak acid with a strong base (where the volume of added base is half of that needed to reach the equivalence point) is equal to pKa for the acid.
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