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Titration and Buffers

Intro to Chemistry Chem1020 Lab. Titration and Buffers. Chemistry Department Minneapolis Community & Technical College. Overview. Part I Introduction Part II NaOH in the flask Part III HCl in the buret Part IV Titration Part V Calculation. Part I. Introduction.

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Titration and Buffers

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  1. Intro to Chemistry Chem1020 Lab Titration and Buffers Chemistry Department Minneapolis Community & Technical College

  2. Overview • Part I Introduction • Part II NaOH in the flask • Part III HCl in the buret • Part IV Titration • Part V Calculation

  3. Part I. Introduction • This experiment is about acid-base reactions in which a proton (H+) is transferred from one reactant to the other : HA + B- A- + HB • Your instructor will demonstrate the part involving a buffer solution. Buffer solutions can resist change in their pH even when a small amount of acid or base is added. This part is discussed in Chapter 16.6 in the textbook. • You will perform the part involving titration, a process in which an HCl solution of unknown concentration is slowly added to a given amount of NaOH solution with known concentration till they react completely with each other. • After the titration, you will determine the concentration of the HCl solution based on other information. This part is discussed in Chapter 15.4 and 15.7 in the textbook.

  4. Part II. NaOH Solution in the Flask Use a medicine dropper to transfer 10.00 ± 0.01 mL into a graduated cylinder. Pour ~30mL into a beaker labeled as “Base” Record this volume of NaOH solution. Record this concentration of NaOH solution. Add 2-3 drops of thymol blue. Pour it into an Erlenmeyer flask.

  5. Part III. HCl Solution in the Buret Covering beaker Remove before starting the experiment, and put it back when all done. Buret clamp Buret Make sure it is secured by the buret clamp. This buret has an incre-ment of 0.1 mL (why?), so all readings should go to the hundredth place with 2 decimal places. Waste beaker It is used to collected all waste solutions. Empty into sink when all done. Valve Now it is in the “OFF” position.

  6. Part III. HCl Solution in the Buret Fill the buret with the help of a funnel to around the “0 mL” mark. Pour ~30mL into a beaker labeled as “Acid” Remove the funnel when done!!! Open the valve to flush the bubbles into the “waste beaker”. Check the buret bottom for bubbles.

  7. Part IV. Titration Read the bottom of the meniscus again and record it as the “Final Reading”. This one should be recorded as 20.41 ± 0.01 mL. Read the bottom of the meniscus in the buret and record it as the “Initial Reading”. E.g. the above volume should be recorded as 0.80 ± 0.01 mL. Close the valve immediately after the solution turns yellow which indicates the completion of the reaction. Put the NaOH solution under the buret and turn on the valve. Keep swirling the flask gently. Make sure to read the buret both before and after the titration!!!

  8. Part IV. Second Trial Empty the content in the Erlenmeyer flask into sink. Rinse the flask first with tap water followed by distilled water. No drying is needed. Repeat steps 3-6 in slide #4 to get NaOH solution ready in the Erlenmeyer flask. Repeat steps 2-4 in slide #6 to get HCl solution ready in the buret. Repeat all steps in slide #7 for titration. To get a more accurate result this time, slow down by adding HCl dropwise when close to the endpoint. Empty the contents in beakers and flask into sink. Rinse first with tap water followed by distilled water. Return everything to your bench. .

  9. Part V. Sample Calculation NaOH Solution HCl Solution

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