Introduction: Here are some informative videos about using a drop counter in titration experiments: https://www.vernier.com/video/acid-base-titration-labquest/ Strong Acid and Base Titration Using Go...

LAB REPORT
PURPOSE OF EXPERIMENT: The determination of Ka by pH titration.
    S.no.
    Reagents required
    Volume / Conc.
    1.
    NaOH
    100 ml 0.5 M
    2.
    KHC8H4O4 or KHP
    25 ml
    3.
    Phenolphthalein
    1 ml
    4.
    Deionized wate
    
REAGENT TABLE:
OTHER REQUIREMENTS: pH electrode, Beaker, Burette, Magnetic sti
er, ring stand clamp, etc.
PROCEDURES: 1. Each group should obtain a burette, a Vernier Lab Quest, a pH probe and a Drop Counter.
2. Plug the pH Probe into the port on the top of the Lab Quest labelled “CH 1” (on the top) and the Drop Counter in the port labelled “DIG 1” (on the side). The display should look like the image to the right.
3. Attach the Drop Counter and a burette clamp to a ring stand such that the Drop Counter is below the burette clamp.
4. Obtain about 100 mL of standardized (approximately 0.1-M) NaOH in a clean dry beaker. Record the exact molarity of the NaOH from the bottle.
5. Using the same techniques learned in previous titration experiments, clean the burette, rinse and flush it with 1 to 2 Ml of the NaOH solution, discard the rinsings and fill the burette with the NaOH solution.
6. You need to make sure that the Drop Counter can “see” each drop that passes through it.
Place the burette filled with the NaOH solution in the burette clamp so that the tip of the burette is just above and approximately centered over the slot in the Drop Counter. Place a waste beaker under the Drop Counter to collect the solution. Turn on the Lab Quest. When it has started you should see that both probes are connected. Press the “Collect” button. Open the stopcock on the burette such that the NaOH solution comes out one drop at a time (about 1 drop every second or two). If it is aligned co
ectly, you should see the volume increase incrementally on the screen. If it is not, adjust the burette side-to-side until the Lab Quest shows the volume changing. When everything is aligned co
ectly close the stop flow of the solution and press the “Collect” button to stop data collection.
7. Calculate the approximate mass of KHP (FM = 204.23) that would be required to neutralize about 25 mL of 0.1-M NaOH.
8. Clean and label two 250 mL or 400 mL beakers (they can be wet). From your professor, obtain a small amount of KHP in a dry shell vial and take the KHP and titration beakers to the analytical balance room. Use the "weighing by difference" technique to place the approximate mass of KHP determined in step 4 into each of the two beakers. Record the 35 mass of KHP in each beaker (±0.0001 g). Obtain approximately 50 mL of the supplied NaOH solution. Be sure to record its molarity.
9. Add approximately 50 mL of distilled water to each beaker and swirl until the KHP is dissolved.
10. Fill a small beaker with distilled water and stand the pH probe in the beaker. The probe should be free from the holder so that it can be moved easily between the beaker and titration beaker.
11. Add a magnetic stir bar to titration beaker 1 and place the beaker under the Drop Counter on top of the magnetic stir plate. Lower the tip of the pH probe through the hole in the Drop Counter into the solution of beaker 1. Turn on the magnetic stir plate and set the speed to the maximum setting.
12. Press “Collect” button on the LabQuest. Open the stopcock on the buret such that the solution flows out one drop at a time at a rate of no more than about 1 drop per second.
13. When pH reaches 11 to 12 and you have added about 2 to 3 mL of solution at that pH you can close the stopcock on the buret and stop the run by pressing the “Collect” button. At this time the contents of beaker 1 can be discarded.
14. Refill the buret with the NaOH solution.
15. Repeat Steps 11 through 13 for beaker 2. Before pressing the “Collect” button, click on the file cabinet icon to add another run to the data collection (Run 2).
GRAPHS
Graph 1a: Run 1
Graph 1b: pH (Run 1) pKa=5
Graph 2a: RUN 2
Graph 2b: Run2 (pH) pKa=5.2
CALCULATION:
· Highest marking of pH for volume in graph 1 AND 3 are the equivalence point where pKa is calculated as pH at half the distance of equivalence.
· According to step 24 in the practical manual taking average of pKa obtained for both the runs.
Calculation: Average of pKa = pKa run 1+ pKa for run 2
----------------------------
2
= 5+5.2/2 = 5.1
pKa = 5.1
Experimental calculation of Ka for KHP
pK = pKa
Ka = 10-5.1
(
K
a
= 7.94 * 10
-6
)
DISCUSSION:
Titration comprises of addition of base to an acid taking place double replacement reaction produces salt and water as a resultant such as NaOH and HCL. Titrating an acid with base results in end point determination. The amount of base required to neutralize an acid. For the determination of end point or equivalence point phenolphthalein is added a pink colour reagent which indicates the neutralization.
Experimental setup requires buret containing base, beaker containing an acid Magnetic sti
er, an indicator. In such a titration, the only data collected are the mass or volume of acid and base that have been added to the titration flask when the equivalence point is reached. However, to construct an acid-base pH titration curve, both pH and burette readings must be recorded after each addition of reagent from the burette. From the volume and molarity of the reagent added, the moles of reagent added can be
Calculated and then this is plotted against pH. Equivalence point further allows us to calculate pKa and further implies to use the:
Henderson-Hasselbalch equation:
In this experiment, an acid-base pH titration curve will be constructed for potassium hydrogen phthalate (KHC8H4O4 or KHP). KHP is a monoprotic acid. An experimental Ka for KHP will be determined in this experiment.
ANSWERS:
Answer 1. No, the mass of KHP used for the pH titration change the experimental value for the
Ka. The mass of KHP is calculated as it is required to neutralize the solution.
Answer 2. pKa = -logka
Kw = (Ka) ( Kb)
Kb = (Kw) / (Ka) = 7.94 * 10-6 / 10-14
Kb = 1.3 * 10-8
Answer 3. Given that, Molarity (M) of KHP = 0.72 M
Kb = 1.3 * 10-8

x = √ (1.3*10-8) (0.72) = 9.67*10-5
pOH= -log (9.67*10-5) = 4.01
Ph+ poh = 14
PH = 14 - pOH = 14 – 4.01 = 9.99
Ph = 9.99
Answer 4. Buffer resists any change in Ph when any weak acid or weak base is added. When solution will reach up to neutralization point this is indicated by an indicator phenolphthalein.
REFERENCES
1. https:
www.vernier.com/video/acid-base-titration-labquest
2. https:
www.youtube.com/watch?v=IJ59Yecn1mY
3. https:
laccd.zoom.us
ec/share/Kjx-ZD-QTfVnyeZj8-mD9wXrJZHpFFRXP7MqWONqgeW_jRLeVgtA2r-zx43UTL15.NEUu9LQHah1b8Czu?startTime=%20XXXXXXXXXX
4. Practical Manual...