Part A: Titration of a weak acid with a strong base
Pipette 25.00 mL of 0.1 M (record the exact molarity actic acid into a dean 400 mL beaker after first placing a magnetic stirring bar on the bottom of the beaker. Add ~150 ml of deionized water and 2 drops of phenolphthalein. Place the beaker on the magnetic stirrer. Lower the electrode into position, approximately one inch above the bottom of the beaker.
Obtain -60 mL of an unknown NaOH solution (for part A) from the front bench. After properly preparing the burette, fill it with unknown NaOH and prepare it for titration. Place it in position to titrate the NaOH solution into the CH:COOH solution, as shown in the diagram.
Read and record the burette reading and pH, both to two decimal places. Add NaOH to the acid slowly. Initially take burette and pH readings after every 2.00 - 3.00 mL addition.
As the equivalence point approaches the pH will rise more rapidly; add smaller (~ 0.10 mL) volumes of NaOH before each pH reading. Start to reduce the volume of each titant addition at a pH of approximately 5.5. Note the volume at which the indicator changes colour. Carry the titration beyond the endpoint, continue with small volume additions until the pH plateaus*, and note how pH changes in this region (add 40.00 mL NaOH in total).
(* when the pH is changing only in the second decimal place, you have reached a plateau)
Part B: Titration of a weak base with a strong acid
Pipette 25.00 mL of 0.1 M (record the exact molarity) ammonia into a clean 400 mL beaker after first placing a magnetic stirring bar on the bottom of the beaker. Add ~150 mL of deionized water and 2 drops of methyl red. Place the beaker on the magnetic stirrer. Lower the electrode into position, approximately one inch above the bottom of the beaker.
Obtain -60 mL of an unknown HCI solution (for part B) from the front bench. After rinsing a burette, fill it with unknown HCI and prepare it for titration. Place it in position to titrate the HCI solution into the ammonia solution.
Read and record the burette reading and pH, both to two decimal places. Add HCI solution to the base slowly. Initially take burette and pH readings after every 2.00 - 3.00 mL addition.
As the equivalence point approaches the pH will drop more rapidly; add smaller (- 0.10 mL) volumes of CI before each pH reading. Start to reduce the volume of each titrant addition at a pil of approximately 8.5. Note the volume at which the indicator changes colour. Carry the tiration beyond the endpoint, continue with small volume additions until the pH plateaus*,
* and note how pH
changes in this region (add 40.00 mL HCl in total).
(* when the pH is changing only in the second decimal place, you have reached a plateau)
Part C: Preparation and Dilution of a Buffer
Use graduated cylinders to measure volumes.
• Obtain 100 mL of 1 M acetic acid and 100 mL of | M sodium acetate solutions from the stock bottles. Record the actual concentrations of these solutions as indicated on the stock bottles. Measure the pH of these two solutions using the ph meter.
• Prepare a buffer solution by mixing 100 mL 1 M acetic acid with 100 mL 1 M sodium acetate solution. Mix well.
• Prepare a 50% buffer solution by adding 100 mL of this buffer to 100 mL deionized water.
• Prepare a 25% buffer solution by adding 100 mL of 50% buffer to 100 mL deionized water.
• Save these buffer solutions for the steps below.
Addition of strong base to buffered and unbuffered solutions:
• Clean the burette used in part A/B, rinse and then fill with 3 M NaOH
• With a graduated cylinder, measure 75 mL of deionized water into a 200 mL Berzelius beaker and place the magnetic stir bar in this solution. Set up your burette, stirrer and pH probe as in part A/B.
Read and record the pH of the sample (in this case deionized water), then, using the burette, add ~1 mL of 3 M NaOH to the sample, read and record the new pH.
Continue adding NaOH in ~1 mL increments until the pH has changed by 3 pH units (for example, if the initial pH is 5.50, add NaOH until the pH is greater than 8.50). After this point, continue to add 2 more ~1 mL NaOH additions. Remember to record the pH after each ~1 mL addition of NaOH.
Discard the solution and rinse the Berzelius beaker before using it in the next steps.
• Repeat the addition of NaOH as above, this time using 75 mL of the 25% buffer. Read and record the pH of the sample before any NaOH is added. Then record the pH after every - 1 mu addition until the pH has changed by 3 pH units, then make two more NaOH additions, recording the pH after each addition.
• Repeat the addition of NaOH as above, this time using 75 mL of the 50% buffer. Read and record the pH of the sample before any NaOH is added. Then record the p after every -1 mi acition until the pH has changed by 3 pH units, then make two more NaOH aditions, recording the pH after each addition.
* Repcat the addition of NaOH as above, this time using 75 mL of the original buffer. Read and additi the pH of the sample before any NaOH is added. Then record the pi after every - mi the pion until the p has changed by 3 pH units, then make two more NaOH aditions, recording
the pH after each addition.
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This is my experiment I will ask you some questions