3. What are the concentrations of each of the following species in 0.100 M Ascorbic acid: H2C6H,O6, НС-Н.Об, СоН06", НзО* and ОН ? (3 роints each) For H2C6H6O6 Kal = 8.0 x 10-5 Ka2 = 1.6 x 10-12 [H2C6H6O6] = [HC6H6O6] = [CH,O²] = [H;O*] = [OH]= %3D

3. What are the concentrations of each of the following species in 0.100 M Ascorbic acid: H2C6H,O6, НС-Н.Об, СоН06", НзО* and ОН ? (3 роints each) For H2C6H6O6 Kal = 8.0 x 10-5 Ka2 = 1.6 x 10-12 [H2C6H6O6] = [HC6H6O6] = [CH,O²] = [H;O*] = [OH]= %3D

Chemistry for Engineering Students

4th Edition

ISBN:9781337398909

Author:Lawrence S. Brown, Tom Holme

Publisher:Lawrence S. Brown, Tom Holme

Chapter12: Chemical Equilibrium

Section: Chapter Questions

Problem 12.65PAE

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Amino acids are an important group of compounds. At low pH, both the carboxylic acid group (CO2H) and the amine group (NHR) are protonated. However, as the pH of the solution increases (say, by adding base), the carboxylic acid proton is removed, usually at a pH between 2 and 3. In a middle range of pHs, therefore, the amine group is protonated, but the carboxylic acid group has lost the proton. (This is called a zwitterion.) At more basic pH values, the amine proton is dissociated. What is the pH of a 0.20 M solution of alanine hydrochloride, [NH3CHCH3CO2H]Cl?
Composition diagrams, commonly known as alpha plots, are often used to visualize the species in a solution of an acid or base as the pH is varied. The diagram for 0.100 M acetic acid is shown here. The plot shows how the fraction [alpha ()] of acetic acid in solution, =[CH3CO2H][CH3CO2H]+[CH3CO2] changes as the pH increases (blue curve). (The red curve shows how the fraction of acetate ion, CH3CO2, changes as the pH increases.) Alpha plots are another way of viewing the relative concentrations of acetic acid and acetate ion as a strong base is added to a solution of acetic acid in the course of a titration. (a) Explain why the fraction of acetic acid declines and that of acetate ion increases as the pH increases. (b) Which species predominates at a pH of 4, acetic acid or acetate ion? What is the situation at a pH of 6? (c) Consider the point where the two lines cross. The fraction of acetic acid in the solution is 0.5, and so is that of acetate ion. That is, the solution is half acid and half conjugate base; their concentrations are equal. At this point, the graph shows the pH is 4.74. Explain why the pH at this point is 4 74.
For conjugate acidbase pairs, how are Ka and Kb related? Consider the reaction of acetic acid in water CH3CO2H(aq)+H2O(l)CH3CO2(aq)+H3O+(aq) where Ka = 1.8 105 a. Which two bases are competing for the proton? b. Which is the stronger base? c. In light of your answer to part b. why do we classify the acetate ion (CH3CO2) as a weak base? Use an appropriate reaction to justify your answer. In general, as base strength increases, conjugate acid strength decreases. Explain why the conjugate acid of the weak base NH3 is a weak acid. To summarize, the conjugate base of a weak acid is a weak base and the conjugate acid of a weak base is a weak acid (weak gives you weak). Assuming Ka for a monoprotic strong acid is 1 106, calculate Kb for the conjugate base of this strong acid. Why do conjugate bases of strong acids have no basic properties in water? List the conjugate bases of the six common strong acids. To tie it all together, some instructors have students think of Li+, K+, Rb+, Cs+, Ca2+, Sr2+, and Ba2+ as the conjugate acids of the strong bases LiOH, KOH. RbOH, CsOH, Ca(OH)2, Sr(OH)2, and Ba(OH)2. Although not technically correct, the conjugate acid strength of these cations is similar to the conjugate base strength of the strong acids. That is, these cations have no acidic properties in water; similarly, the conjugate bases of strong acids have no basic properties (strong gives you worthless). Fill in the blanks with the correct response. The conjugate base of a weak acid is a_____base. The conjugate acid of a weak base is a_____acid. The conjugate base of a strong acid is a_____base. The conjugate acid of a strong base is a_____ acid. (Hint: Weak gives you weak and strong gives you worthless.)
Malic acid is a weak diprotic organic acid with Ka1 = 4.0 104 and Ka2 = 9.0 105. a Letting the symbol H2A represent malic acid, write the chemical equations that represent Ka1 and Ka2. Write the chemical equation that represents Ka1 Ka2. b Qualitatively describe the relative concentrations of H2A, HA, A2, and H3O+ in a solution that is about one molar in malic acid. c Calculate the pH of a 0.0175 M malic acid solution and the equilibrium concentration of [H2A]. d What is the A2 concentrationin in solutions b and c?
Two strategies are also followed when solving for the pH of a base in water. What is the strategy for calculating the pH of a strong base in water? List the strong bases mentioned in the text that should be committed to memory. Why is calculating the pH of Ca(OH)2 solutions a little more difficult than calculating the pH of NaOH solutions? Most bases are weak bases. The presence of what element most commonly results in basic properties for an organic compound? What is present on this element in compounds that allows it to accept a proton? Table 13-3 and Appendix 5 of the text list Kb values for some weak bases. What strategy is used to solve for the pH of a weak base in water? What assumptions are made when solving for the pH of weak base solutions? If the 5% rule fails, how do you calculate the pH of a weak base in water?
Strong Acids, Weak Acids, and pH Two 0.10-mol samples of the hypothetical monoprotic acids HA(aq) and HB(aq) are used to prepare 1.0-L stock solutions of each acid. a Write the chemical reactions for these acids in water. What are the concentrations of the two acid solutions? b One of these acids is a strong acid, and one is weak. What could you measure that would tell you which acid was strong and which was weak? c Say that the HA(aq) solution has a pH of 3.7. Is this the stronger of the two acids? How did you arrive at your answer? d What is the concentration of A(aq) in the HA solution described in part c? e If HB(aq) is a strong acid, what is the hydronium-ion concentration? f In the solution of HB(aq), which of the following would you expect to be in the greatest concentration: H3O+(aq), B(aq), HB(aq), or OH(aq)? How did you decide? g In the solution of HA(aq), which of the following would you expect to be in the greatest concentration: H3O+(aq), A+(aq), HA(aq), or OH(aq)? How did you decide? h Say you add 1.0 L of pure water to a solution of HB. Would this water addition make the solution more acidic, make it less acidic, or not change the acidity of the original solution? Be sure to fully justify your answer. i You prepare a 1.0-L solution of HA. You then take a 200-mL sample of this solution and place it into a separate container. Would this 200 mL sample be more acidic, be less acidic, or have the same acidity as the original 1.0-L solution of HA(aq)? Be sure to support your answer.
How many mEq of HCO3 are present in a solution that also contains 75 mEq of Na+, 83 mEq K+, 10 mEq Ca2+, and 153 mEq Cl?
. How is the strength of an acid related to the fact that a competition for protons exists in aqueous solution between water molecules and the anion of the acid?
Consider a solution prepared by mixing a weak acid HA. HCl, and NaA. Which of the following statements best describes what happens? a. The H+ from the HCl reacts completely with the A from the NaA. Then the HA dissociates somewhat. b. The H+ from the HCl reacts somewhat with the A from the NaA to make HA, while the HA is dissociating. Eventually you have equal amounts of everything. c. The H+ from the HCl reacts somewhat with the A from the NaA to make HA while the HA is dissociating. Eventually all the reactions have equal rates. d. The H+ from the HCl reacts completely with the A from the NaA. Then the HA dissociates somewhat until too much H+ and A are formed, so the H+ and A react to form HA, and so on. Eventually equilibrium is reached. Justify your choice, and for choices you did not pick, explain what is wrong with them.
The pH of a solution of Ba(OH)2 is 10.66 at 25 . What is the hydroxide ion concentration in the solution? If the solution volume is 125 mL, what mass of Ba(OH)2 must have been dissolved?
Consider the following six beakers. All have 100 mL of aqueous 0.1 M solutions of the following compounds: beaker A has HI beaker B has HNO2 beaker C has NaOH beaker D has Ba(OH)2 beaker E has NH4Cl beaker F has C2H5NH2 Answer the questions below, using LT (for is less than), GT (for is greater than), EQ (for is equal to), or MI (for more Information required). (a) The pH in beaker A the pH in beaker B. (b) The pH in beaker C the pH in beaker D. (c) The % ionization in beaker A the % ionization in beaker C. (d) The pH in beaker B the pH in beaker E. (e) The pH in beaker E the pH in beaker F. (f) The pH in beaker C the pH in beaker F.
Which of the diagrams in Problem 10-135 represents the substance that is the weakest electrolyte?