onlinelab by cuiliqing

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									                               Part I. Unknown Acid and Base Problem
                            Determining the pKa of a weak acid and weak base

Name _______________________________             Section __________ Date ____________

This homework uses the virtual lab. Using a computer that is running Microsoft windows or Macintosh OS 10.1 or
higher, go to http://ir.chem.cmu.edu and click on “Run Virtual Lab” in the left-hand selection under students.

To load the assignment, select “Load Homework...” from the “File” menu, and select “Acids and Bases : Unknown
Acid and Base Problem ”.

(Q & A Quote from the website: “Our observations of new users indicate that 5 minutes of exploration is typically
sufficient for students to learn the essential features of the Virtual Lab. You can help by walking them through the
step-by-step sample titration problem that illustrates all of the features in context. A user guide that explains the
function of each feature is also available to answer questions about specific Virtual Lab tools or features.”)

1) (7.5 pts) The “Homework Solutions” cabinet contains a solution labeled "Unknown Acid,"
which is a weak mono-protic acid with an unknown Ka and with an unknown concentration.
Your job is to determine the concentration and Ka to two significant figures. Please report your
results and explain your procedure.
2) (7.5 pts) The cabinet labeled “Homework Solutions” also contains a solution labeled
"Unknown Base," which is a base with an unknown Kb and with an unknown concentration.
Your job is to determine the concentration and Kb to two significant figures. Please report your
results and explain your procedure.
                            Part II. pKa and weak acid assignment:
                Determining the pKa and concentration ratio of a protein in solution.

Name _______________________________          Section __________ Date ____________

This homework uses the virtual lab. Using a computer that is running Microsoft windows or Macintosh OS 10.1 or
higher, go to http://ir.chem.cmu.edu and click on “Run Virtual Lab” in the left-hand selection under students.

To load the assignment, select “Load Homework...” from the “File” menu, and select
         “Acids and Bases : pKa and weak acid problem ”.

This assignment utilizes a protein that acts as a weak acid, according to the equation:
                       HProtein + H2O <--> Protein- + H3O+ Ka(Protein)

1) (3 pts) The cabinet named Homework contains a solution labeled “Protein”. This solution
contains a dilute mixture of the protein and HCl. What is Ka of the protein? (Please show your
work.)




2) (5 pts) Based on you answer to part 1, at what pH will the ratio [Protein-]/[HProtein] = 0.75?
(Please show your work.)
3) (7 pts) Create 100ml of solution such that when you add between 1 and 5ml of the protein
solution of part 1, the ratio [Protein-]/[HProtein] = 0.75. Please test that your solution works.
Also please describe what you did, and report the solutions and amounts you mixed together to
make your 100ml solution.

								
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