Table of Contents ALL LABS CHEM 1211K-Titrations Lab Handout
CHEM 1211K - Titrations Lab Handout
4. Repeat calculations 1-3 for Trials 2 and 3.
5. Calculate the average value of the molarity of the HCI.
Analysis & Discussion:
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1. Based on your three trials, discuss the precision of your data.
2. The actual concentration of the unknown is 0.200 M. Calculate the percent error based on the average molarity of your three trials.
3. Based on your answer to (2), discuss the accuracy of your data.
4. Discuss the potential sources of error that could have affected either/both your accuracy and precision.
(Examples could include items such as: a) You forgot to rinse the burette with the NaOH solution; b) Bubbles of air were trapped in the burette tip; c) You added 10 drops
of phenolphthalein instead of 5 drops; d) The meniscus of NaOH was sitting right on the 32 line so you reported the reading as 32 mL instead of 32.00 mL. ) Explain HOW
and WHY each of these may have impacted your results.
5. 80.0 mL of 0.30 M NaOH and 80.0 mL of 0.30 M HCl are mixed together. What is the approximate pH of this solution - acidic, basic, or neutral? Explain.
6. A 0.8159 g sample of HCI was placed into a 50 mL volumetric flask and the sample was thoroughly dissolved in water to make 50 mL of solution. It required 22.07 mL of
NaOH to reach the endpoint in the titration. What is the molarity of the NaOH solution?
Conclusion
>/n1. Using your volumetric data for Trial 1, calculate the moles of NaOH required to reach the equivalence point.
2. Based on the answer to (1), for Trial 1, calculate the moles of HCl originally present in your solution.
3. Based on the answer to (2), for Trial 1, calculate the original concentration (in units of molarity) of the HCl solution.
4. Repeat calculations 1-3 for Trials 2 and 3.
5. Calculate the average value of the molarity of the HCI./nTable 1: Titration Data for Unknown
Unknown Identifier
Volume of unknown (mL)
Initial burette reading (mL)
Final burette reading (mL)
Volume Titrant Added (mL)
Calculated Molarity of HCI
(M)*
Average Molarity (M)*
10.0mL
Trial 1
73.5mL
38.5mL
35.0mL
0.35
0.35
Trial 2
10.0mL
76.8mL
41.8mL
35.0mL
0.35
10.0
Trial 3
76.8mL
41.8mL
35.0mL
0.35/nAnalysis of Unknown Strong Acid Solution
1. Obtain a ring stand, 50 mL burette, and a burette clamp.
2. Attach the burette clamp to the ring stand and clamp the burette in place, making sure the tip is about a foot above the table top.
3. Fill the burette with approximately 15 mL of the standardized 0.100 M NaOH solution; drain and refill it with -25 mL of 0.100 M NaOH solution. Wipe the outside of the
burette to ensure it is free of liquid.
4. Obtain an unknown HCl solution from your instructor. Record the unknown number on your report form.
5. Use a 10.00 mL volumetric pipet to quantitatively transfer a precise amount of 10.00 mL of of the unknown HCl solution to a 50 mL Erlenmeyer flask (Reminder to not
pipet directly from the stock bottle.) (The flask has to be clean, but not dry-why not?) Add 5 drops of phenolphthalein indicator.
6. Place the Erlenmeyer flask with your analyte under the burette.
7. Record the initial burette reading (to the nearest 0.01 mL) in Table 1. Carefully add titrant until you start to see the color start to change to pink. Manually swirl your
Erlenmeyer flask to ensure complete mixing. You have reached the endpoint when the pale pink color persists.
8. Once you have reached the endpoint, record the final burette reading (to the nearest 0.01 mL) in Table 1. Use the initial and final readings to determine the volume of titrant
added and record this value in Table 1.
9. Repeat this at least 2 times for sufficient practice. Record the initial burette reading, final burette reading, and volume of titrant added for each sample in Table 1 (you should
have three in total).
Note: If one of your "Volume titrant added" measurements is more than 10% off from the other two values, re-do this trial until you achieve consistent results.
