g

txt

School

Western Governors University *

*We aren’t endorsed by this school

Course

1

Subject

Chemistry

Date

Nov 24, 2024

Type

txt

Pages

3

Uploaded by zaq12wsx19

Report
Period ___ Date ___/___/___ 18 • Reactions between Acids and Bases ALKA SELTZER™ LABETTE Equipment: 4 plastic cups 1 Alka Seltzer tablet glass stir rod distilled water 1 M HCl 10% vinegar solution universal indicator 1 M NaOH I. pH Change of Distilled Water: 1. Pour distilled water into the four cups until they are about half- filled. To each cup add 10 drops of universal indicator. Stir. Set two cups aside for Part II. Add a drop of 1 M HCl to one cup. Stir. Can you observe any color (pH) change? Repeat. Add a drop of 1 M NaOH to the other cup. Stir. Do you observe any color (pH) change? Repeat. 2. Write your observations about how easily the color changes with added acid or base: II. pH Change of Alka Seltzer Solution: 3. Break the Alka Seltzer tablet into two halves. Add one half to each of the two cups with distilled water and universal indicator. Add a drop of 1 M HCl to one cup. Stir. Can you observe any color (pH) change? Repeat. Add a drop of 1 M NaOH to the other cup. Stir. Do you observe any color (pH) change? Repeat. 4. Write your observations about how different the Alka Seltzer solution acts compared to water: III. Why Does This Happen? Alka Seltzer contains the weak acid, citric acid, which we will write as HA. The dissociation equilibrium for HA is: HA H+ + A 5. HA is a proton ________ (donor / acceptor) A is a proton ________ (donor / acceptor) 6. Using Le Châtelier's Principle, indicate the effect of the following changes: HA H+ + A add H+ ___ ___ ___ add OH ___ ___ ___ 7. In Alka Seltzer, the lack of color change is due to the fact that the added H+ ions are almost all used up and the removed H+ ions are almost all replaced. Added H+ ions are almost all absorbed by ______. H+ ions (removed by OH) are almost all replaced by _______. The solution contains large numbers of donors (weak acid) and acceptors (conjugate base). HA H+ +  8. Solutions with large concentrations of acids (proton donors) and bases (proton acceptors)
that do not neutralize each other are called ___________. IV. Let’s Make A Buffer (a.k.a. “Half Titration”) 9. We can make the conjugate base of a weak acid (HC2H3O2) by neutralizing the acid with NaOH. The conjugate base of HC2H3O2 is: _____________ 10. Write the neutralization equation for HC2H3O2 with NaOH. Circle HC2H3O2’s conjugate base. 11. Rinse out your four cups. Put diluted vinegar into one cup and split the liquid equally into two cups. Add 10 drops of universal indicator to each cup. Neutralize the acid in one cup by adding 1 M NaOH. When will you know you have added enough NaOH? _____________________ 12. In the cup of neutralized acid, essentially all of the HC2H3O2 has been changed to __________. 13. Mix the two cups together, pour about ¼ of your mixture into a clean cup (for Part V), and split the remaining liquid evenly between the two cups. What is the color (pH) of the mixture? _____ 14. Test the two samples (as you did with the Alka Seltzer) to see if they are a buffer. Write your observations about whether this solution acts as a buffer: V. Buffering Capacity Take the small amount of buffer from Step 13 above. Fill the cup almost full with distilled water. Split the solution between the two cups. Add more universal indicator to each cup if needed. Test the two samples (as you did with the Alka Seltzer) to see whether they act as a buffer. 15. Write your observations about the “buffering capacity” of the diluted buffer: VI. Calculation 16. The equilibrium of a buffer is the same as the equilibrium of the dissociation of an acid. Write the dissociation equation for HC2H3O2. Ka = 1.8 x 10-5. Use HAc as an abbreviation. 17. In your mixture (Step 13 above), how does [HAc] compare to [Ac]? ____________ 18. Write the Ka expression for HAc: 19. If [HAc] = [Ac], the expression changes to: 20. What is the significance of the pKa? 21. The pH of this buffer must be _______ (Relate to color observed in Step 13 above.) 22. The most effective buffer is made from large equal concentrations of the acid and its conjugate base. In this case, the pH = pKa. What is the pH of the best buffer made from the following acids? a) HCN Ka = 4.0 x 10-10 The pH of the best buffer is _____. b) HF Ka = 7.2 x 10-4 The pH of the best buffer is _____. c) HClO Ka = 3.5 x 10-8 The pH of the best buffer is _____.
23. For HAc, the pH of the best buffer is: ______ If you wanted a buffer with a pH of 5.00, however, would you need to add more acid, HAc, or more base, Ac? ______ 24. Determine the ratio of [Ac] to [HAc] that would form a buffer with a pH of 5.00? _______ Use the Henderson-Hasselbalch equation: pH = pKa + log
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
  • Access to all documents
  • Unlimited textbook solutions
  • 24/7 expert homework help

Related Documents

Q22.png
Discussion Week 7 + Tut7.pdf
Online Class Activity.docx
Week 16 Recitation worksheet (final exam review).pdf
IMG-20231207-WA0001.jpg
wsfsdswq.pdf
A2A2F782-39A2-4E38-AA71-2199DB1D8914.jpeg
Screenshot 2023-12-02 at 12.37.40 PM.png
things_to_know_for_unit_2_test.docx
Farmacia Quimica.doc
equilibriumpracticetest.pdf
stoichiometry_and_heat_capacity.pdf
Recommended textbooks for you
Text book image
Chemistry
Chemistry
ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher:Cengage Learning
Text book image
Chemistry: An Atoms First Approach
Chemistry
ISBN:9781305079243
Author:Steven S. Zumdahl, Susan A. Zumdahl
Publisher:Cengage Learning
Text book image
Chemistry
Chemistry
ISBN:9781133611097
Author:Steven S. Zumdahl
Publisher:Cengage Learning
Text book image
Chemistry: Principles and Practice
Chemistry
ISBN:9780534420123
Author:Daniel L. Reger, Scott R. Goode, David W. Ball, Edward Mercer
Publisher:Cengage Learning
Text book image
Chemistry: Principles and Reactions
Chemistry
ISBN:9781305079373
Author:William L. Masterton, Cecile N. Hurley
Publisher:Cengage Learning
Text book image
General Chemistry - Standalone book (MindTap Cour...
Chemistry
ISBN:9781305580343
Author:Steven D. Gammon, Ebbing, Darrell Ebbing, Steven D., Darrell; Gammon, Darrell Ebbing; Steven D. Gammon, Darrell D.; Gammon, Ebbing; Steven D. Gammon; Darrell
Publisher:Cengage Learning
SEE MORE TEXTBOOKS
Recommended textbooks for you
  • Text book image
    Chemistry
    Chemistry
    ISBN:9781305957404
    Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
    Publisher:Cengage Learning
    Text book image
    Chemistry: An Atoms First Approach
    Chemistry
    ISBN:9781305079243
    Author:Steven S. Zumdahl, Susan A. Zumdahl
    Publisher:Cengage Learning
    Text book image
    Chemistry
    Chemistry
    ISBN:9781133611097
    Author:Steven S. Zumdahl
    Publisher:Cengage Learning
  • Text book image
    Chemistry: Principles and Practice
    Chemistry
    ISBN:9780534420123
    Author:Daniel L. Reger, Scott R. Goode, David W. Ball, Edward Mercer
    Publisher:Cengage Learning
    Text book image
    Chemistry: Principles and Reactions
    Chemistry
    ISBN:9781305079373
    Author:William L. Masterton, Cecile N. Hurley
    Publisher:Cengage Learning
    Text book image
    General Chemistry - Standalone book (MindTap Cour...
    Chemistry
    ISBN:9781305580343
    Author:Steven D. Gammon, Ebbing, Darrell Ebbing, Steven D., Darrell; Gammon, Darrell Ebbing; Steven D. Gammon, Darrell D.; Gammon, Ebbing; Steven D. Gammon; Darrell
    Publisher:Cengage Learning
Text book image
Chemistry
Chemistry
ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher:Cengage Learning
Text book image
Chemistry: An Atoms First Approach
Chemistry
ISBN:9781305079243
Author:Steven S. Zumdahl, Susan A. Zumdahl
Publisher:Cengage Learning
Text book image
Chemistry
Chemistry
ISBN:9781133611097
Author:Steven S. Zumdahl
Publisher:Cengage Learning
Text book image
Chemistry: Principles and Practice
Chemistry
ISBN:9780534420123
Author:Daniel L. Reger, Scott R. Goode, David W. Ball, Edward Mercer
Publisher:Cengage Learning
Text book image
Chemistry: Principles and Reactions
Chemistry
ISBN:9781305079373
Author:William L. Masterton, Cecile N. Hurley
Publisher:Cengage Learning
Text book image
General Chemistry - Standalone book (MindTap Cour...
Chemistry
ISBN:9781305580343
Author:Steven D. Gammon, Ebbing, Darrell Ebbing, Steven D., Darrell; Gammon, Darrell Ebbing; Steven D. Gammon, Darrell D.; Gammon, Ebbing; Steven D. Gammon; Darrell
Publisher:Cengage Learning
SEE MORE TEXTBOOKS