Concept explainers
Calculate the pH at
Interpretation:
The pH of the solution that contains phosphoric acid with given concentration is to be determined.
Concept introduction:
The first ionization of the polyprotic acid takes place as
The second ionization of the polyprotic acid takes place as
The third ionization of the polyprotic acid takes place as
Percent ionization is the percentage of acid that gets dissociated upon addition to water. It depends on the hydronium ion concentration.
Here,
pH of the solution is calculated as
Answer to Problem 88QP
Solution:
The pH of the solution is
Explanation of Solution
Given information:
The concentration of phosphoric acid
When phosphoric acid is dissolved in water, the dissociation takes place in three steps as it is a triprotic acid. First, one proton is partially dissociated because phosphoric acid is a weak acid. Thus, the pH of the solution is determined by the contribution made by all the three proton dissociation steps.
The reaction of the first proton dissociation of phosphoric acid is depicted as
Prepare an equilibrium table and represent each of the species in terms of
Now, substitute these concentrations in equation (1) as
Because the value of
Thus,
Calculate the percent dissociation from equation (4) as
Since the percent dissociation is more than
Since concentration cannot be negative, so
Thus,
Now, the reaction of the second proton dissociation of phosphoric acid is depicted as
Prepare an equilibrium table and represent each of the species in terms of
Now, substitute these concentrations in equation (2) as
Since the value of
Thus,
Calculate the percent dissociation from equation (4) as
Since the percent dissociation is much less than
Now, the reaction of the third proton dissociation of phosphoric acid is depicted as
Prepare an equilibrium table and represent each of the species in terms of
Now, substitute these concentrations in equation (3):
Since the value of
Thus,
Calculate the percent dissociation from equation (4) as
Since the percent dissociation is much less than
Also,
Substitute this value in equation (5) to calculate pH of the solution:
The pH of the phosphoric acid solution is
Want to see more full solutions like this?
Chapter 16 Solutions
Chemistry
- The pH of a 0.10-M solution of propanoic acid, CH3CH2COOH, a weak organic acid, is measured at equilibrium and found to be 2.93 at 25 °C. Calculate the Ka of propanoic acid.arrow_forward12.62 Write the formula of the conjugate acid of each of the following bases, (a) OH-, (b) NHj, (c) CHjNHt, (d) HPO/-, (e) CO.,2’arrow_forwardLactic acid, C3H6O3, occurs in sour milk as a result of the metabolism of certain bacteria. Calculate the pH of a solution of 56. mg lactic acid in 250. mL water. Ka for D-lactic acid is 1.5 × 10−4.arrow_forward
- What is the pH of a solution obtained by mixing 235 mL of NaOH with a pH of 11.57 and 316 mL of Sr(OH)2 with a pH of 12.09? Assume that volumes are additive.arrow_forwardThe base ethylamine (CH3CH2NH2) has a Kb of. A closely related base, ethanolamine(HOCH2CH2NH2), has a Kb of 3.2105. (a) Which of the two bases is stronger? (b) Calculate the pH of a 0.10M solution of the strong base?arrow_forwardA solution of acetic acid, HC2H3O2, on a laboratory shelf was of undetermined concentration. If the pH of the solution was found to be 2.57, what was the concentration of the acetic acid? The Ka of acetic acid is 1.7 105.arrow_forward
- Classify each of the following substances as an acid, a base, or a salt. a. AlPO4 b. KOH c. HNO3 d. HC2H3O2arrow_forwardCalculate [OH-] and pH in a solution in which the hydrogen sulfite ion, HSO3-, is 0.429 M and the sulfite ion is (a) 0.0249 M (b) 0.247 M (c) 0.504 M (d) 0.811 M (e) 1.223 Marrow_forwardHydrazine, N2H4 (having the structure H2NNH2), and its derivatives have been used as rocket fuels. Draw the Lewis electron-dot formula for the hydrazine molecule. Describe the geometries expected about the nitrogen atoms in this molecule. Why would you expect hydrazine to be basic? Which substance, NH3 or N2H4, would you expect to be more basic? Why? Write the chemical equation in which hydrazine reacts with hydrochloric acids to form the salt N2H5Cl. Consider the positive ion of this salt. How does its basic character compare with that of NH3 and N2H4? Explain.arrow_forward
- Chemistry: Principles and ReactionsChemistryISBN:9781305079373Author:William L. Masterton, Cecile N. HurleyPublisher:Cengage LearningChemistry: Principles and PracticeChemistryISBN:9780534420123Author:Daniel L. Reger, Scott R. Goode, David W. Ball, Edward MercerPublisher:Cengage LearningChemistry: The Molecular ScienceChemistryISBN:9781285199047Author:John W. Moore, Conrad L. StanitskiPublisher:Cengage Learning
- Introductory Chemistry: A FoundationChemistryISBN:9781285199030Author:Steven S. Zumdahl, Donald J. DeCostePublisher:Cengage LearningChemistry & Chemical ReactivityChemistryISBN:9781337399074Author:John C. Kotz, Paul M. Treichel, John Townsend, David TreichelPublisher:Cengage LearningChemistry & Chemical ReactivityChemistryISBN:9781133949640Author:John C. Kotz, Paul M. Treichel, John Townsend, David TreichelPublisher:Cengage Learning