PSI AP Chemistry Name______Chapter Problems Part D: Acid-Base Reactions

Classwork: 1. A student is in possession of an unknown organic acid that is one of the acids below: H2C2O4 H2C4H4O5

The student dissolves 3.00 grams of the acid in water to prepare a 50 mL solution of the acid and then fully titrates the acid with standardized 0.4 M KOH. The student found that 112 mL was needed to reach the endpoint of the titration. a) Write a balanced reaction of the base with either of the two acids shown above: b) What is the molar mass of the acid and identify the acid. c) How many mL of 0.8 M KOH would be needed to titrate the acid found in “b”? d) How many mL of 0.4 M KOH would have been needed to titrate an equivalent molar amount of the other acid? e) How many mL of 0.4 M KOH would have been needed to titrate a solution of HCN assuming an equal number of moles of HCN as there were of the acid found in “b”?

2. Write the proper reaction for the following: a. Solid calcium hydroxide is added to an ammonium chloride solution b. Aqueous potassium hydroxide is used to titrate a hydroiodic acid solution. c. A nitrous acid solution is added to a sodium carbonate solution

3. Citric acid (H3C6H5O7) is an important metabolite in living organisms. a. What is the conjugate base of citric acid? b. Write the reaction of citric acid with water. (assume only one H is donated) c. How many mL of 0.4 M NaOH would be needed to convert all citric acid into HC6H5O72-? d. How many mL of 0.4 M NaOH would be needed to convert all citric acid to the citrate ion (C6H5O73-)? e. Which of the following is amphoteric (H2C6H5O7- or C6H5O73-)? Justify your answer.

4. A 0.2 M acetic acid (HC2H3O2) solution dissociates 1.5% in water. a. What is the equilibrium concentration of the acetate ion in such a solution? b. If acetic acid were a strong acid (IT’S NOT!), what would be the concentration of acetate ion in the solution? www.njctl.org AP Chemistry Mole Concept, Reactions, Stoichiometry

Answers Classwork: 1. A student is in possession of an unknown organic acid that is one of the acids below: H2C2O4 H2C4H4O5

The student dissolves 3.00 grams of the acid in water to prepare a 50 mL solution of the acid and then fully titrates the acid with standardized 0.4 M KOH. The student found that 112 mL was needed to reach the endpoint of the titration. a) Write a balanced reaction of the base with either of the two acids shown above: H2C2O4 + 2OH-  2H2O + C2O42- H2C4H4O5 + 2OH-  2H2O + C4H4O52- b) What is the molar mass of the acid and identify the acid. 134 g/mol = H2C4H4O5 c) How many mL of 0.8 M KOH would be needed to titrate the acid found in “b”? 56 mL d) How many mL of 0.4 M KOH would have been needed to titrate the other acid? 112 mL e) How many mL of 0.4 M KOH would have been needed to titrate a solution of HCN assuming an equal number of moles of HCN as there were of the acid found in “b”? 56 mL

2. Write the proper reaction for the following: a. Solid calcium hydroxide is added to an ammonium chloride solution Ca(OH)2(s) + 2NH4+(aq)  2NH3(aq) + Ca2+(aq) + 2H2O(l) b. Aqueous potassium hydroxide is used to titrate a hydroiodic acid solution. OH-(aq) + H+(aq)  H2O(l) c. A nitrous acid solution is added to a sodium carbonate solution HNO2(aq) + CO32-(aq)  H2CO3(aq) + NO2-(aq)  CO2(g) + H2O(l) + NO2-(aq)

3. Citric acid (H3C6H5O7) is an important metabolite in living organisms. a. What is the conjugate base of citric acid? H2C6H5O7- Also acceptable: HC6H5O7-2 C6H5O7-3 b. Write the reaction of citric acid with water. (assume only one H is donated) www.njctl.org AP Chemistry Mole Concept, Reactions, Stoichiometry

H3C6H5O7(aq) + H2O(l)  H2C6H5O7-(aq) + H3O+(aq) c. How many mL of 0.4 M NaOH would be needed to convert all citric acid in a 10 mL 0.5 M citric acid solution into HC6H5O72-? 25 mL d. How many mL of 0.4 M NaOH would be needed to convert all citric acid in the previous problem to the citrate ion (C6H5O73-)? 37.5 mL e. Which of the following is amphoteric (H2C6H5O7- or C6H5O73-)? Justify your answer. H2C6H5O7- as it can both accept H+ ions and donate them while the citrate ion can only act as a base 4. A 0.2 M acetic acid (HC2H3O2) solution dissociates 1.5% in water. a. What is the equilibrium concentration of the acetate ion in such a solution? 0.003 M If acetic acid were a strong acid (IT'S NOT!!!), what would be the concentration of acetate ion in the solution? 0.2 M

www.njctl.org AP Chemistry Mole Concept, Reactions, Stoichiometry