Titration of a Stong and Weak Acid Short Answer Titration of Strong and Weak Aci

Question

Titration of a Stong and Weak Acid

Short Answer

Titration of Strong and Weak Acids

Experiment 1: Titrate a Strong Acid

*** TITRATED WITH 1M Sodium Hydroxide***

**Procedures included for clarity, short answer and lab notes below.

Experiment 1: Titrate a Strong Acid

Take an Erlenmeyer flask from the Containers shelf and place it onto the workbench.

Take hydrochloric acid (unknown concentration) from the Materials shelf and add 25.00 mL to the Erlenmeyer flask. Record this volume in your Lab Notes. Remember to press Save Notes.

Take phenolphthalein from the Materials shelf and add 2 drops to the flask.

Take a burette from the Containers shelf and place it onto the workbench.

Take sodium hydroxide from the Materials shelf and add 50.00 mL to the burette.

Take a pH meter from the Instruments shelf and place it into the flask. Record the initial pH of the solution in your Lab Notes.  

Move the Erlenmeyer flask onto the base of the burette.

Perform a coarse titration:

Add large amounts (~1.00 mL) of the sodium hydroxide from the burette by pressing and holding the stopcock at the bottom of the burette. Check the dispensed volume after each addition of NaOH. To do this, pass the mouse cursor over the burette and a gray tool tip will briefly display the dispensed volume as well as the volume remaining in the burette.

For every 1.00 mL added, record the dispensed volume and pH in your Lab Notes. As the sodium hydroxide is added to the hydrochloric acid solution the pH increases.

Check if the end point has passed. When the reaction reaches the end point, the solution changes color. Record the volume dispensed and pH for both the last volume where the solution was colorless and the first volume where the solution was pink in your Lab Notes. This gives you the range within which to do the fine titration.

Add additional titrant in 1.00 mL increments and record the pH after each dispensation in your Lab Notes. Add a total of 5.00 mL extra. This data will be used to plot the titration curve.

Clear your station by dragging the Erlenmeyer flask and burette to the recycle bin beneath the workbench.

Repeat steps 1 – 8 to set up the fine titration. You can skip step 6 because the pH meter is not mandatory for the fine titration.

Perform a fine titration:

Quickly add titrant by clicking and holding the burette's stopcock. Add 1.00 mL less than was needed for a color change in your coarse titration. This is near, but not yet at the titration's end point.

Add titrant one drop at a time until the end point is reached. Record the volume dispensed in your Lab Notes.

Clear your station by dragging the Erlenmeyer flask and burette to the recycling bin.

Repeat the fine titration once more. Record the results in your Lab Notes. If the results from the two fine titrations do not closely agree, perform a third fine titration to determine which titration was done incorrectly.

Experiment 2: Titrate a Weak Acid

Repeat the procedure in experiment 1, steps 1 – 10, using 5.00 mL of acetic acid #2 (unknown concentration) diluted with 20.00 mL of water as analyte, 1.00 M sodium hydroxide as titrant, and phenolphthalein as indicator. The acetic acid is diluted with water to better visualize the end point color change. Remember to press Save Notes.

Lab Results

Record the following results in the table below. If you performed more than two fine titrations, discard the volume that was most different.

Data Analysis

1. Find the equivalence point on the graph. What is the pH and dispensed volume of NaOH at this point?

2. Calculate the molarity of the HCl solution.

Experiment 2: Titrate a Weak Acid

Lab Results

Record the following results in the table below. If you performed more than two fine titrations, discard the volume that was most different.

Data Analysis

3. Find the equivalence point on the graph. What is the pH and dispensed volume of NaOH at this point?

4. Calculate the molarity of the acetic acid solution.

Conclusions

5. How did the titrations of the two acids compare? Did the results align with the differences between strong and weak acids?

6. The table below contains the pKa values of four weak acids. Which acid is the weakest?

Lab Notes:

25 mL of hydrochloric acid
Initial pH: .95

First Dispense:
Volume: 48.87 mL
Volume Dispensed: 1.13 mL
pH: 1.20

Second Dispense:
Volume: 47.66 mL
Volume Dispensed: 2.34
pH: 1.78

Third Dispense: END POINT REACHED
Volume: 46.68 mL
Volume Dispensed: 3.32 mL
pH: 12.26

Fourth Dispense
Volume: 45.64 mL
volume dispensed: 4.36 mL
pH: 12.73

Fifth Dispense:
Volume: 44.51 mL
Volume Dispensed: 5.49 mL
pH: 12.93

Sixth Dispense:
Volume: 43.40 mL
Volume Dispensed: 6.60 mL
pH: 13.06

Seventh Dispense:
Volume: 42.24 mL
Volume Dispensed: 7.76 mL
pH:13.16

Eight Dispense:
Volume: 41.28 mL
Volume Dispensed: 8.72 mL
pH: 13.22

Ninth Dispense:
Volume: 40.33 mL
Volume Dispensed: 9.67 mL
pH: 13.27

Fine Titration 1:
Volume: 47.17 mL
Volume dispensed: 2.83 mL

Fine Titration 2:
Volume: 47.18 mL
Volume Dispensed: 2.82 mL

EXPERIMENT 2
Initial: 5 mL acetic acid (unknown), 20 mL water
Initial pH: 2.78

First Dispense:
Volume: 49.14 mL
Volume Dispensed: 0.86 mL
pH: 4.20

Second Dispense:
Volume: 48.02 mL
Volume Dispensed: 1.98 mL
pH: 4.75

Third Dispense:
Volume: 46.07 mL
Volume Dispensed: 3.93 mL
pH: 6.51

Fourth Dispense: END POINT REACHED
Volume: 44.92 mL
Volume Dispensed: 5.08 mL
pH: 12.55

Fifth Dispense:
Volume: 43.98 mL
Volume Dispensed: 6.02 mL
pH: 12.80

Sixth Dispense:
Volume: 42.89 mL
Volume Dispensed: 7.02 mL
pH:12.96

Seventh Dispense:
Volume: 41.85 mL
Volume Dispensed: 8.15 mL
pH: 13.08

Eighth Dispense:
Volume: 40.94 mL
Volume Dispensed: 9.06 mL
pH: 13.15

Ninth Dispense:
Volume: 39.82 mL
Volume Dispensed: 10.18 mL
pH: 13.22

Fine Titration 1
Volume: 45.96 mL
Volume Dispensed: 4.04 mL

Fine Titration 2:
Volume: 45.98 mL
Volume Dispensed: 4.02 mL

volume of NaOH dispensed in the coarse titration (mL) 3.32 mL volume of NaOH dispensed in the first fine titration (mL) 2.83 mL volume of NaOH dispensed in the second fine titration (mL) 2.82 mL average volume of NaOH dispensed in the fine titrations (mL) 2.825 mL color of indicator at end point Pink

Explanation / Answer

Ans

Experiment 1 : Titration of strong acid

moles of NaOH added = molarity of NaOH x Volume of NaOH

let say we added 5 ml NaOH to reach end point

moles of NaOH = moles of strong acid = 1 M x 5 ml = 5 mmol

Molarity of HCl solution = 5 mmol/50 ml = 0.1 M

Experiment 2 : Titration of weak acid

volume of NaOH dispensed = 1 ml

moles of NaOH = moles of weak acid = 1 M x 1 ml = 1 mmol

Molarity of weak acid = 1 mmol/25 ml = 0.04 M

Conclusions

A strong acid require higher volume of NaOH to reach th end point with equivalence point pH = 7.

A weak acid required smaller smount of NaOH to reach the end point with equivalence point pH = basic > 7

From the table below, the weakest acid would have the highest pKa

Weakest acid = H2CO3

Thus, H2CO3 has lowest dissociation constant Ka, small amount of acid dissoicates at equilibrium in solution.

Related Questions

Navigate

• Browse (All)
• Browse T
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.