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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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

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.

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.

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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Textbook Question

Two buffers are prepared by adding an equal number of moles of formic acid (HCOOH) and sodium formate (HCOONa) to enough water to make 1.00 L of solution. Buffer A is prepared using 1.00 mol each of formic acid and sodium formate. Buffer B is prepared by using 0.010 mol of each. (b) Which buffer will have the greater buffer capacity?

Textbook Question

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?

Textbook Question

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?