lap report exp 14

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ASSIGNMENT INSTRUCTIONS FOR EXPT 14 (Identification of an Unknown Acid)

This is a full lab report with all the usual sections, except, of course, you won’t have any lab notebook pages to scan.
Also: you didn’t (and wouldn’t have) prepared a standard oxalic acid solution, and you wouldn’t have standardized the NaOH solution — an already-standardized NaOH solution would have been provided to you (and this is assumed in the data you’re given). You don’t have to write about or mention the standardization parts of this lab (the first two parts of the procedure).

Notice that this assignment contains some simulations of actual lab procedures and data generation — read through these instructions carefully before beginning work.

Title page

Objective

  • Write all objectives of this experiment. Use complete sentences.

Introduction

The introduction must explain these points, in a narrative style. Don’t just reiterate the procedure here — the Introduction should be a bit of story-telling about why you did what you did to achieve your goals.

  • What is a titration? What is the purpose of a titration experiment?
  • How can a titration be used to identify an unknown substance?
  • How can a melting point be used to identify an unknown substance?
  • 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?
  • How can pKa determination be used to identify an unknown substance?
  • For a weak acid, under what conditions will pH = pKa?

Procedure

  • Cite the manual
  • Include any modifications to the procedure
    • This lab will skip:
      • Preparation of the Standard Oxalic Acid Solution
      • Standardization of NaOH

Results and Calculations

Use the results that were provided to you. Find your personalized, unique results in a PDF file, with your name at the end of the file name, in the separate module “Expt 14 (Unknown Acid) Procedure Videos and Additional Info”.

Molar Mass of a Monoprotic Unknown Acid

Use the data that was provided to you to determine the molar mass of the unknown acid.

  • First calculate number of moles of NaOH that was needed to neutralize all the acid.
  • Use stoichiometry to determine how many moles of acid must have been present in the titration experiment.
  • Use the mass of the acid and the moles of the acid present in the titration to determine the molar mass.
  • Calculate the molar mass for each trial
    • Calculate an average and a standard deviation

The Melting Point

Follow the link that was provided to you with the rest of your data. Assume that the video represents the same unknown that was analyzed in the titration.

  • Watch the video and record an appropriate melting point range for your unknown substance.

Measuring pKa

Use the data given to you.

  • For each trial, calculate the volume of NaOH that is needed to reach the half-equivalence point. Use the same concentration of NaOH as with the titration.
  • Use the link (https://tinyurl.com/tjfamdz) (Links to an external site.) to access the virtual pH meter. The website simulates a pH meter. It is a GoogleDoc that is shared with all sections of CHEM 141 offered this semester. If another student is using the website, please wait. You can tell that another student is logged on by finding an icon in the upper right. Hovering over the icon with your mouse pointer usually reads “Anonymous”. (see image below). If it looks like no one is logged on or if it doesn’t look like anyone is actively using the site, go a head and continue.
  • Another user using GoogleSheet.PNG
    • If the last user left their data, go ahead and erase it (but you should be certain no one is still actively using the site!!!)
    • Enter your values for trial 1
      • Fill in the 4 green boxes. The website does not check your answers. If you input the wrong values, you’ll get a bad pH reading (or you’ll get an error).
      • The website does some calculations elsewhere and it can take a few seconds for the pH in the red box to update. Once it updates, record your pH.
    • Repeat for any other trials.
    • When you are done, delete your data so it’s ready for the next user
    • Finally, close the browser or tab. Otherwise your icon will show when other students open the page and they might think you’re still using the site!
    • Calculate a mean and standard deviation for the pKa.
  • Organize your results into a table that makes it easy to compare the major results.

Calculations

  • Type out all of your calculations:
    • Molar mass of unknown.
    • Calculation for the half equivalence point.

Discussion

Remember that reports are writing assignments. Writing should be organized into topics and written in well-developed paragraphs. Paragraphs should be arranged in a fashion that demonstrates a logical progression of ideas.

  • Your discussion must include the following:
    • The identity of your unknown
    • The experimental molar mass
    • The experimental melting point for your unknown
    • The experimental pKa for your unknown
    • The theoretical molar mass
    • The literature melting point for your unknown (with a citation for the reference)
    • The literature pKa for your unknown
    • The precision and accuracy of your results
    • Sources of error that might occur in the laboratory setting. Miscalculation is not a legitimate source of error. If you miscalculated something, you should identify the mistake and fix it. “Human error” is vague and not a legitimate source of error error. Try to think of addressable sources of error that can be taken into consideration to improve the experiment if it had to be repeated in the lab.

Conclusion

  • Write a conclusion:
    • Report your main findings.
      • Specifically, give the resolution to the objectives.
    • Remember to be quantitative and report the most important numerical findings.

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