Acid-Base Titrations - Lab for Chem 163 PDF

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Lab for Chem 163...

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CHEM 163L Fall 2018 - Mary Franzis Knoeferl Weekly Notes/Week 12 PDF Version generated by

Mary Franzis Knoeferl on Nov 11, 2018 @02:41 PM CST

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Weekly Notes/Week 12

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Week 12 Mary Franzis Knoeferl Nov 07, 2018 @06:20 PM CST

Acid-Base Titrations Mary Franzis Knoeferl Nov 07, 2018 @06:20 PM CST

Mary Knoeferl

Weekly Notes/Week 12

3 of 8 Mary Franzis Knoeferl Nov 07, 2018 @06:21 PM CST

Pre-Lab Mary Franzis Knoeferl Nov 07, 2018 @07:15 PM CST

Investigation Questions 1. What is titration? 2. What is a titrant and an analyte? 3. What is an indicator and how is it used?

General Titration Instructions: 1. Get the sample of acid you will be titrating. Pipet the solution so you know the volume of the solution you used as accurately as is possible. If the solution is highly concentrated you may need to add some water before titrating. 2. Put 10 drops of indicator in the flask so you will know when the reaction is complete. The indicators are usually made up in very dilute solutions in water or alcohol. If the lab bench is a dark color it will be hard to see the color change no matter how much indicator you use. Put a piece of white paper under the flask so you can see the color of the solution in the flask. 3. Put the solution of the base in the buret, using the following method: Empty the distilled water. Close the stopcock and add about 3 mL of the base solution to the buret using a funnel. Turn the buret so it is nearly horizontal, without letting the base run out of the open end. While you hold the buret nearly horizontal, roll it in your fingers so the base solution touches every park of the inside of the buret. Hold it upright and open the stopcock to drain the base through the tip into the beaker. Repeat this rinsing twice to completely wet the buret. Hold it upright and open the stopcock to drain the base through the tip into the beaker. Repeat. 4. Remove air bubbles from the buret tip. To remove these bubbles, put a beaker under the tip and open and shut the stopcock quickly as often as is required to remove the bubbles. Refill the buret using a funnel if the volume of base removed was too large. 5. Record the level of the solution in the buret before you start. The volume of base added will be the difference between the ending volume and starting volume. You can record the volume to 0.01 mL. 6. Titration: Hold the flask with the acid in it in one hand under the tip of the buret and swirl. Open the stopcock and watch the color as you swirl the flask. Use the stopcock to control the flow. When you begin to see signs of the endpoint slow the rate at which you are adding the base and continue swirling the flask. When it begins to spread throughout the solution stop the flow of base and keep swirling. After each drop of base hits the solution the endpoint color appears, spreads and disappears. When the color is spreading almost throughout the solution, stop adding base and keep swirling. Add one drop of base and stop while swirling. When the addition of one drop of base changes the color of the whole solution to the endpoint color and this color remains in the solution you have reached the endpoint. 7. After your last titration, empty the base from the buret into the beaker containing your base rinsings. Neutralize the base with dilute acid. Rinse the buret with distilled water three times as you did with the base when you started. Fill the buret with distilled water and put a small rubber stope in the open end. Store the buret in the buret clamp as you found it.

Chemicals and Safety Information For all: wear gloves and goggles Sodium hydroxide - may cause severe burns Hydrochloric acid - corrosive and irritant for skin, eye contact, and ingestion Vinegar - may cause eye, skin, digestive tract, and respiratory tract irritation; this is a lab supply and may not be ingested Aspirin - may cause eye, skin, digestive tract, and respiratory tract irritation; this is a lab supply and may not be ingested Ethanol, 95% - flammable; may cause blindness or be fatal if swallowed; keep this at the reagent bench and away from burners

Part 1 Procedure:

Weekly Notes/Week 12

1. Fill the buret with 50 mL of 0.1 M NaOH 2. With a graduated pipette, add 25.00 mL of unknown HCl solution into a 250-mL beaker. Add 10 drops of phenolphthalein indicator. Using a clean graduate pipette, add 25 mL of distilled water to the solution. 3. Record the initial colors of both the NaOH and HCl solutions. 4. Using the digital PH meter, record the initial pH of the HCl solution in the beaker. Continue to record the pH after every 2 mL of NaOH has been added. 5. Gradually dispense some of the NaOH solution solution drop-by-drop from the buret into the solution in the beaker. Note any color changes observed, and so so constantly. Continue to record the pH after every 2 mL of NaOH has been added. 6. As the equivalence point is approached, a pinkish color will appear and dissipate more slowly as the titration proceeds. Now add the NaOH dropby-drop until the endpoint of the titration is reached. Begin measuring the pH more often. 7. Record the volume of NaOH required to reach the endpoint of the titration and the pH of the solution. 8. Continue to add NaOH to the HCl solution until 45-50 mL of NaOH has been added. Continue to record the pH every 2 mL and also record any observations. Record the final pH.

Part 2 Procedure: 1. Get a vinegar sample, just a little more than you plan to use, in a 30-mL beaker. Read the bottle label and record the concentration of acetic acid as reported on the label. 2. Plan with your partner how you want to prepare and measure the volume of the sample you will titrate. 3. Add the phenolphthalein indicator and titrate with the sodium hydroxide solution.

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Weekly Notes/Week 12

5 of 8 Mary Franzis Knoeferl Nov 08, 2018 @09:14 AM CST

Procedure Changes, Raw Data, and Observations Mary Franzis Knoeferl Nov 08, 2018 @11:09 AM CST

Part 1 Trial 1: The initial colors of the NaOH and HCl solutions are both clear. Initial pH of HCl - 1.58 pH of HCl with 2 mL of NaOH - 2.47

Trial 2: The initial colors of the NaOH and HCl solutions are both clear. Initial pH of HCl - 1.57 Initial reading at miniscus (mL)

Final reading at miniscus(mL)

7.4

35.4

Actual (mL) 28

17.5

45.2

27.7

Part 2A Concentration of acetic acid - 5% Initial reading at miniscus (mL)

Final reading at miniscus (mL)

22.8

54.2

Initial reading at miniscus (mL)

Final reading at miniscus (mL)

2.8

16.7

Actual (mL) 31. 4

Part 2B The aspirin is 325 mg per tablet Actual (mL) 13.9

Weekly Notes/Week 12

6 of 8 Mary Franzis Knoeferl Nov 09, 2018 @04:32 PM CST

Analysis Mary Franzis Knoeferl Nov 11, 2018 @02:18 PM CST

Analysis Questions Part 1: 1. Initial reading at meniscus (mL) Final reading at meniscus (mL) Total volume (mL)

2.

3.

7.4

35.4

28

17.5

45.2

27.7

Weekly Notes/Week 12

The red circles in these graphs represent the equivalence point in each trial. 4. The unknown solution is basic at the equivalence point. 5.

Analysis Questions Part 2: 1. As an alternative to performing another titration, we considered finding the density of vinegar to find its concentration. 2. We used a graduated pipette. 3. The volume of the vinegar is essential in the concentration equation to find the concentration

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Weekly Notes/Week 12

8 of 8 Mary Franzis Knoeferl Nov 09, 2018 @05:11 PM CST

Reflective Writing Mary Franzis Knoeferl Nov 11, 2018 @02:40 PM CST

Explain: Titration is the process of finding the concentration of a substance using another substance with a known concentration. The titrant is the substance where the concentration is known and the analyte is the substance where the concentration is unknown. An indicator is a liquid that turns a different color when the pH of a solution changes. It is often used to determine if a chemical reaction has taken place. Evaluate: My results were consistent with what was expected. The solutions reached the equivalence point at about the same point that the pH of the solution read 7, or neutral. Additionally, my results were consistent with the class results. For the most part, the other groups in the lab found similar equivalence points. If I were to perform this lab again, I would have performed more trials in order to get more consistent results. Extend: This lab relates to the lab we performed earlier in the semester about concentration because the concentration was calculated in this lab. Mary Franzis Knoeferl Nov 09, 2018 @05:11 PM CST...