Rubric For Indicators Buffer Lab

CHEM 1112, Dr. Stone Spring 2014

Grading Rubric for Indicators and Buffers

Title, Purpose, Procedure, 1 point
Data analysis for Part A
1. 2 points: For each solution determine what ion is expected to hydrolyze if any and the spectator ions if any.
2. 2 points: Based in the colors of the indicators, determine the pH of the solutions, calculate [H+] and [OH-].
3. 4 points: For those solutions where ions hydrolyze, write the net ionic equation for hydrolysis, the expression for equilibrium constant Ka or Kb and the equilibrium constant value Ka or Kb. Compare those values to literature values and calculate % difference.
4. 1 point: Compare the pH of a 0.1 M solution of sodium acetate with the pH of a 0.1 M solution of potassium acetate.

Data Analysis for Part B
Show neat calculations for the following:
1. 2 points: Calculate pH of original buffer.
2. 1 point: Calculate pH of buffer + HCl.
3. 1 point: Calculate pH of buffer + NaOH
4. 1 point: Calculate pH of buffer + NaOH + filtered water
5. 1 point: Compare calculated values with the values measured with the pH meter and calculate the % difference. Put these values in a neat table.

Conclusion, 3 points
What indicators did you use? (List them in order of their pKa values.) Restate the Ka or Kb values for each solution that you tested. Restate the % difference for each Ka or Kb value. What must be present for a solution to be a buffer? What is the function of buffers? How do they work? What happened when strong acid or base was added to your buffer solution?

References: 1 point
You need to have at least one, with correct citing format: Author(s), title, year, journal title, volume, pages.

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