Ch.4 - Reactions in Aqueous Solution

Problem 106a

Chapter 4, Problem 106a

(a) By titration, 15.0 mL of 0.1008 M sodium hydroxide is needed to neutralize a 0.2053-g sample of a weak acid. What is the molar mass of the acid if it is monoprotic?

Verified step by step guidance

Step 1: Write the balanced chemical equation for the neutralization reaction. For a monoprotic acid (HA) reacting with sodium hydroxide (NaOH), the equation is: HA + NaOH -> NaA + H2O.

Step 2: Calculate the moles of NaOH used in the titration. Use the formula: \( \text{moles of NaOH} = \text{volume (L)} \times \text{molarity (M)} \). Convert 15.0 mL to liters by dividing by 1000.

Step 3: Since the acid is monoprotic, the moles of acid (HA) will be equal to the moles of NaOH used, as the reaction is a 1:1 ratio.

Step 4: Calculate the molar mass of the acid. Use the formula: \( \text{molar mass} = \frac{\text{mass of acid (g)}}{\text{moles of acid}} \).

Step 5: Substitute the known values (mass of acid and moles of acid) into the molar mass formula to find the molar mass of the acid.

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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. In this process, a solution of known concentration (the titrant) is gradually added to a solution of unknown concentration until the reaction reaches its endpoint, which is often indicated by a color change. This method is commonly used in acid-base reactions to find the amount of acid or base present in a sample.

Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It is calculated by summing the atomic masses of all the atoms in a molecule. In the context of the question, determining the molar mass of the weak acid involves using the amount of acid neutralized by the known volume and concentration of sodium hydroxide during the titration.

Monoprotic Acid

A monoprotic acid is an acid that can donate only one proton (H⁺ ion) per molecule during a reaction. This characteristic simplifies the stoichiometry of acid-base reactions, as the number of moles of the acid will equal the number of moles of base at the equivalence point. In this case, knowing that the acid is monoprotic allows for straightforward calculations to find its molar mass based on the titration data.

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Related Practice

Textbook Question

Suppose you have 3.00 g of powdered zinc metal, 3.00g of powdered silver metal and 500.0 mL of a 0.2 M copper(II) nitrate solution. (a) Which metal will react with the copper(II) nitrate solution?

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Textbook Question

Suppose you have 3.00 g of powdered zinc metal, 3.00g of powdered silver metal and 500.0 mL of a 0.2 M copper(II) nitrate solution. (b) What is the net ionic equation that describes this reaction?

Textbook Question

Suppose you have 3.00 g of powdered zinc metal, 3.00g of powdered silver metal and 500.0 mL of a 0.2 M copper(II) nitrate solution. (d) What is the molarity of Cu²⁺ ions in the resulting solution?

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Textbook Question

(b) An elemental analysis of the acid indicates that it is composed of 5.89% H, 70.6% C, and 23.5% O by mass. What is its molecular formula?

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Textbook Question

The discovery of hafnium, element number 72, provided a controversial episode in chemistry. G. Urbain, a French chemist, claimed in 1911 to have isolated an element number 72 from a sample of rare earth (elements 58–71) compounds. However, Niels Bohr believed that hafnium was more likely to be found along with zirconium than with the rare earths. D. Coster and G. von Hevesy, working in Bohr's laboratory in Copenhagen, showed in 1922 that element 72 was present in a sample of Norwegian zircon, an ore of zirconium. (The name hafnium comes from the Latin name for Copenhagen, Hafnia). (c) Solid zirconium dioxide, ZrO2, reacts with chlorine gas in the presence of carbon. The products of the reaction are ZrCl4 and two gases, CO2 and CO in the ratio 1:2. Write a balanced chemical equation for the reaction.

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Open Question

A fertilizer railroad car carrying 129,840 L of commercial aqueous ammonia (30% ammonia by mass) tips over and spills. The density of the aqueous ammonia solution is 0.88 g/cm³. What mass of citric acid, C₆H₈O₇ (which contains three acidic protons), is required to neutralize the spill?