Ch.4 - Reactions in Aqueous Solution

Problem 148

Chapter 4, Problem 148

Salicylic acid, used in the manufacture of aspirin, contains only the elements C, H, and O and has only one acidic hydrogen that reacts with NaOH. When 1.00 g of salicylic acid undergoes complete combustion, 2.23 g CO2 and 0.39 g H2O are obtained. When 1.00 g of salicylic acid is titrated with 0.100 M NaOH, 72.4 mL of base is needed for complete reaction. What are the empirical and molecular formulas of salicylic acid?

Verified step by step guidance

Determine the moles of CO2 and H2O produced from the combustion of salicylic acid. Use the molar mass of CO2 (44.01 g/mol) and H2O (18.02 g/mol) to convert the mass of each product to moles.

Calculate the moles of carbon and hydrogen in the original sample of salicylic acid. Assume all carbon in CO2 comes from salicylic acid and all hydrogen in H2O comes from salicylic acid. Use the stoichiometry of CO2 (1 mole of C per mole of CO2) and H2O (2 moles of H per mole of H2O).

Determine the mass of oxygen in salicylic acid by subtracting the mass of carbon and hydrogen from the total mass of salicylic acid. Convert this mass to moles using the molar mass of oxygen (16.00 g/mol).

Calculate the empirical formula of salicylic acid by finding the simplest whole number ratio of moles of C, H, and O. Divide the moles of each element by the smallest number of moles among them.

Determine the molecular formula using the titration data. Calculate the molar mass of salicylic acid by using the volume and molarity of NaOH (0.100 M) required to neutralize the acid. Compare this molar mass to the mass of the empirical formula to find the molecular formula.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.

Video duration:

Was this helpful?

Key Concepts

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

Empirical Formula

The empirical formula represents the simplest whole-number ratio of the elements in a compound. To determine it, one must first calculate the moles of each element present in the compound based on experimental data, such as combustion products. For salicylic acid, the moles of carbon, hydrogen, and oxygen can be derived from the amounts of CO2 and H2O produced during combustion.

Molecular Formula

The molecular formula indicates the actual number of atoms of each element in a molecule of the compound. It can be derived from the empirical formula by determining the molar mass of the compound and comparing it to the molar mass of the empirical formula. In the case of salicylic acid, the molecular formula can be found by using the mass of the sample and the volume of NaOH used in titration to find the molar mass.

Titration

Titration is a quantitative analytical technique used to determine the concentration of a solute in a solution. In this scenario, the titration of salicylic acid with NaOH allows for the calculation of the number of moles of the acid present, which is essential for determining its empirical formula. The volume of NaOH used in the titration directly relates to the amount of acidic hydrogen in salicylic acid, providing critical data for the analysis.

Recommended video:

Guided course

03:04

Acid-Base Titration

Related Practice

Textbook Question

A mixture of acetic acid (CH3CO2H; monoprotic) and oxalic acid (H2C2O4; diprotic) requires 27.15 mL of 0.100 M NaOH to neutralize it. When an identical amount of the mixture is titrated, 15.05 mL of 0.0247 M KMnO4 is needed for complete reaction. What is the mass percent of each acid in the mixture? (Acetic acid does not react with MnO4 equation for the reaction of oxalic acid with MnO4 given in Problem 4.133.)

1110

views

Textbook Question

Iron content in ores can be determined by a redox procedure in which the sample is first reduced with Sn2+, as in Problem 4.130, and then titrated with KMnO4 to oxidize the Fe2+ to Fe3+. The balanced equation is What is the mass percent Fe in a 2.368 g sample if 48.39 mL of a 0.1116 M KMnO4 solution is needed to titrate the Fe3 + ?

306

views

Textbook Question

A mixture of FeCl2 and NaCl is dissolved in water, and addi-tion of aqueous silver nitrate then yields 7.0149 g of a pre-cipitate. When an identical amount of the mixture is titrated with MnO4 -, 14.28 mL of 0.198 M KMnO4 is needed for complete reaction. What are the mass percents of the two compounds in the mixture? (Na+ and Cl-do not react with MnO4 -. The equation for the reaction of Fe2+ with MnO4 was given in Problem 4.146.)

891

views

Textbook Question

Compound X contains only the elements C, H, O, and S. A 5.00 g sample undergoes complete combustion to give 4.83 g of CO₂, 1.48 g of H₂O, and a certain amount of SO₂ that is further oxidized to SO3 and dissolved in water to form sulfuric acid, H₂SO₄. On titration of the H₂SO₄, 109.8 mL of 1.00 M NaOH is needed for complete reaction. (Both H atoms in sulfuric acid are acidic and react with NaOH.) (a) What is the empirical formula of X?

628

views

Textbook Question

(b) When 5.00 g of X is titrated with NaOH, it is found that X has two acidic hydrogens that react with NaOH and that 54.9 mL of 1.00 M NaOH is required to completely neu-tralize the sample. What is the molecular formula of X?

434

views

Textbook Question

A 1.268 g sample of a metal carbonate (MCO3) was treated with 100.00 mL of 0.1083 M sulfuric acid (H2SO4), yielding CO2 gas and an aqueous solution of the metal sulfate (MSO4). The solution was boiled to remove all the dissolved CO2 and was then titrated with 0.1241 M NaOH. A 71.02 mL volume of NaOH was required to neutralize the excess H2SO4. (a) What is the identity of the metal M?

524

views