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The purpose of the Identification of an Unknown Acid is to teach you how to use multiple pieces of data to determine the identity of a compound

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The purpose of the Identification of an Unknown Acid is to teach you how to use multiple pieces of data to determine the identity of a compound. This type of problem solving is used in forensics, drug discovery, and applied fields such as medicine.

Skills:

In this lab report, you will:

• Determine the identity of an unknown monoprotic acid from a list of possibilities by using
  • Molar mass
    • Determined by mass measurement and titration
  • Melting point
    • Determined by MelTemp or Fischer Johns Melting Temperature instrument
  • pKa
    • Determined by pH measurement at the half-equivalence point using a pH meter

Knowledge:

This assignment will also help you to become familiar with the following important content information:

• Understand how a titration is performed
• How to determine the endpoint of a titration and understand its significant
• Calculate the molar mass of an unknown monoprotic acid based on titration results
• Define monoprotic acid
• Make correct volume measurements using a buret
• Recognize the different stages of melting and record an accurate melting range
• Define half-equivalence point and how to calculate it
• Understand how to estimate the pKa of a weak acid

Tasks:

This exercise asks you to complete the following

• Prelab Quiz 1, 2, and 3
• Title Page
• Objective
  • What was the goal of this experiment? What data will you use to accomplished it?
• Introduction
  • Define gram molar mass aka equivalent weight.
  • Define titration. What is the purpose of a titration experiment?

• What is a primary standard? What was the primary standard in this experiment? (If you didn't use a primary standard, indicate what it should have been))
• Why were there 2 standard solutions? That is, why wasn’t NaOH(aq) used as a primary standard for titrating the unknown acid? (If you didn't use a primary standard, then explain why NaOH(aq) should be used as a primary standard.
• How would melting of a pure sample differ from melting of an impure sample?
• What is Ka? What is pKa? What does a high Ka mean? What does a high pKa mean?
• What is a buffer?
• For a weak acid, under what conditions will pH = pKa?

• Procedure Reference
  • What changes were made to the published procedures?
• Results and Calculations
  • Use the results that were provided to you.
    • Create a table summarizing your major experimental data (i.e. gram molar mass, melting point, and pKa of monoprotic unknown acid).
    • Show sample calculations.
  • Summarize the gram molar mass, melting point, and pKa of your top monoprotic acids with percent error values.
• Discussion
  • State the identity of your unknown acid.
    • Discuss how you came to that conclusion using your average gram molar mass with standard deviation and average melting point range to justify your identification.
    • Explain how you narrowed down the suspects and state your second choice and/or third choice, if appropriate and how they were eliminated.
    • Be sure to discuss, how many standard deviations the actual molar mass of the acid you believe best represents your unknown is away from the experimental molecular mass of the acid.
    • Also, does the actual melting point of your identified acid fall within the range of your experimental average melting points? Explain why or why not.
    • Discuss the accuracy and precision of your average gram molar mass and melting point.
  • Discuss any sources of error that may have occurred in the experiment. For example, if you added too much base to one of your titrations, you should identify how that would have affected your gram molar mass calculation.
• Conclusion
  • Evaluate the objective of the experiment and restate the identity of your unknown acid, the average gram molar mass and the average melting point range.
• Post Lab Questions
• Spreadsheet
• Provided Data

Criteria for Success:

Be sure to complete the prelab quizzes, and the full formal lab report (i.e. title page, objective, introduction, procedure reference with changes noted, results and calculations section, discussion, and conclusion), post lab questions, spreadsheet, and provided data.

• Ask your instructor any questions that you may have as you complete the assignment.
• Remember that all previous criteria for lab reports apply to this write-up.
• Before the start of lab on the due date:
  • Use AdobeScan to take pictures of your prelab questions, report sheets, and post lab questions. Combine these with the word document containing your computer-generated images.