Titrations Discussion, chemistry homework help

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In your discussion you should make a conclusion and then explain how your experimental results and observations support your conclusion. The points below should help you identify the information you have available from this experiment to support your conclusion. Finish completed lab report by the due date. Be sure to include:

    1. a. Purpose. Based upon the introduction in the uploaded files, what are you trying to find with your experiment?
    2. b. Claim. Based upon the purpose of your experiment, what claim can you make using your experimental evidence?
    3. c. Table(s) of your results. Include expected, experimental, and % error as appropriate.
    4. d. Discussion of your results.
    5. e. Uncertainty and Error in measurements.
      1. Identify possible sources of uncertainty and error in your measurements.
      2. Use evidence from your laboratory notebook to support your error analysis.
      3. Discuss how the direction of each source of error affects the results.
    6. f. Supporting references.

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Experiment 5: Titrations Question: How can we determine the concentration of acid in vinegar? Goals 1. Students use acid-base reactions to determine the concentration of a sodium hydroxide solution. 2. Students apply acid-base reactions to determine the concentration of a sample of vinegar. 3. Students learn the concept of a primary standard. Objectives 1. Students carry out acid-base titrations. 2. Students determine necessary accuracy and precision for an analysis. Introduction Background: A local vinegar company is about to bottle its latest batch of product. However, their in-house tests of quality have been inconsistent and they are not sure what the concentration of the latest batch is. The manufacturer has contacted WITS – Widener Independent Testing Services – to determine the concentration to make sure it falls within the acceptable range for its product. You are the top chemist at WITS. Your supervisor has obtained a sample of the vinegar from the company. You will have 100 mL of vinegar, and with that, you will need to determine density and % acetic acid. The acceptable density range is 1.000 to 1.004 g/mL, and the acceptable range of acetic acid is 4.95 to 5.05% by weight. A 5% by weight (w/w) solution has 5 grams of acetic acid in 100 grams of solution. The company needs to know within the week if they can bottle this batch or if they need to have a waste company dispose of it. This is a new potential testing business for WITS, so a procedure needs to be developed. The procedure should take into account determining the concentration of the sodium hydroxide solution that you will use to titrate the vinegar solution in addition to the titration procedure itself. Consider the number of significant figures you need to generate in order to provide the vinegar company with the information they need. Be sure to include enough replicates so that you can have confidence in your results. In addition, safety information needs to be obtained for acetic acid and for the materials below. Your supervisor is very excited about this new business opportunity and is anxiously awaiting your results. Equipment 1. Magnetic stirring plates and stir bars 2. 100 mL graduated cylinder 3. Analytical balances (to 0.0001 g) 4. 50 mL buret 5. 5 mL, 10 mL, and 25 mL pipet Reagents 1. Sodium hydroxide solution, unknown concentration 2. Potassium hydrogen phthalate, a solid acid which can be used as a standard 3. Phenolphthalein indicator solution 4. Unknown vinegar Resources 1. http://science.widener.edu/svb/video/titration1.wmv 2. http://science.widener.edu/~svanbram/local/saunders/05m14vdl. mov 3. CRC Handbook of Chemistry and Physics - You may use any edition 4. NIOSH Pocket Guide to Chemical Hazards (NPG) - http://www.cdc.gov/niosh/npg/ 5. SIRI MSDS Database - http://siri.org/msds/index.php 6. Chemistry Laboratory Information Profiles, CD-ROM or http://www.acs.org/content/acs/en/about/governance/committ ees/chemicalsafety/safetypractices/clips-list.html 7. Comprehensive Guide to Chemical Resistant Best Gloves - http://www.chemrest.com/ Safety and Pre-Lab Before starting the experiment, complete the Safety and Pre-Lab template. For this experiment, your Pre-Lab includes an experimental procedure. Provide step-by-step detail with sufficient detail for another student in the class to exactly repeat your experiment. Be specific. Your procedure should clearly state what data and observations need to be recorded during the experiment. Procedure Your Pre-Lab assignment for this experiment is to write a procedure. Submit the draft to your instructor by the due date. A revised version will be due when you turn in your lab reports. Recognize that amounts you will use may differ significantly from those you may find in literature procedures, as the concentrations may differ. It would be helpful to consider the expected value of acetic acid concentration in vinegar and calculate expected volumes ahead of time. Your procedure should include the following: Standardize your sodium hydroxide solution. Sodium hydroxide does not come as a pure solid and the solution reacts with carbon dioxide in the atmosphere. Since your calculations depend on accurately knowing this concentration, it is important that you standardize your sodium hydroxide solution. The solution is approximately 0.25 M and you will standardize it by titrating using potassium hydrogen phthalate (KHP). Each student should complete three replicates. After you have completed the standardization, you can determine the concentration of the acetic acid in the vinegar sample by titrating it with your sodium hydroxide solution. Each student should complete three replicates. As an additional check, you need to determine the density of the vinegar sample. Make sure you determine the density of a known solution so that you can prove your experimental technique is valid and reliable. Dispose of all waste solutions in the container in the instructor hood located at the front of the lab.
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Explanation & Answer


Titration Procedure
First, to use acid-base reactions to determine the concentration of sodium hydroxide solution.
Secondly, to determine the concentration of acetic acid in vinegar using acid-base reactions.
Finally, to help the students understand the concept of primary standard.
To carry out acid-base titrations to the required accuracy and precision in order to determine the
concentration of acetic acid in vinegar.
Sodium hydroxide absorbs water and carbon dioxide from the atmosphere, and react to form
sodium carbonate and sodium bicarbonate thus the need for standardization before acid base
Magnetic stirring plates and stir bars.
100 mL graduated cylinder.
Analytical balances (to 0.0001g).
50 mL burette.
5 mL, 10 mL, and 25 mL pipet.
Sodium hydroxide solution, unknown concentration.
Potassium hydrogen phthalate, a solid acid which has been used as a standard.
Phenolphthalein indicator solution.
Vinegar, unknown concentration.
Part 1: Standardization of sodium hydroxide solution.
1. Measure the mass of a reasonable amount of solid potassium hydrogen phthalate using
the analytical balance.
2. Dissolve the measured KHP in distilled water.
3. Add 2 to 3 drops of phenolphthalein indicator to the KHP solution.
4. Rinse the burette using sodium hydroxide solution.
5. Add sodium hydroxide solution to the burette and record the initial volume.

6. Titrate until the KHP solution just turns pink and persists even with stirring.
7. Record the final burette reading and repeat the titration three more times, recording the
Results and Discussion.

Mass KHP

Vol NaOH Initial

Vol NaOH Final

Vol NaOH Used













The table above shows the volume of sodium hydroxide solution used to completely neutralize
potassium hydrogen phthalate solution. The volume used is obtained by subtraction the initial
volume of sodium hydroxide from the final volume as shown below.
22.5 - 0.4 = 22.1
20.4 – 0.1 = 20.3
20.8 – 0.6 = 20.2
18.2 – 0.0 = 18.2
The number of moles of potassium hydrogen phthalate can be accurately determined, for each
titration, using the mass and the molar mass of the compound.
The molar mass of KHP is 204.22 mol/g
Number of moles = Mass/ molar mass
Therefore: Where the mass is 0.8436,
No. of moles = 0.8436 g / 204.22 mol/g = 0.004131 moles
Where the mass is 0.8321,
No. of moles = 0.8321 g / 204.22 mol/g = 0.004075 moles
Where the mass is 0.8284,
No. of moles = 0.8284 g / 204.22 mol/g = 0.004056 moles
Where the mass is 0.7303,

No. of moles = 0.7303 g / 204.22 mol/g = 0.003576 moles
Sodium Hydroxide and potassium hydrogen...

Really useful study material!


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