Acid-Base Titration  Lab #1

Purpose:  To successfully titrate a weak acid against a strong base and determine the concentration of the weak acid as well as picking an apporpriate acid-base indicator that is suitable for this particular reaction.

The acid will be either formic or ethanoic acid which will have been prepared for you.  The base will be potassium hydroxide which you will have to prepare.

Part 1.  Generation of the KOH solution
1. Weigh out between 2-4 grams of KOH accurately to at least 2 decimal places.
2. Dissolve in distilled water in a volumetric flask. Swirl the contents to fully dissolve the KOH.
3.  When dissolved, top up the volumetic flask to the mark.

Part 2.   Standardization of the KOH solution with benzoic acid.
1. Fill a clean, rinsed burette with the KOH solution.
2.  Mass out approximately 0.2-0.5 grams of benzoic acid and record the mass used accurately to two decimal places.
3. Benzoic acid is a weak acid.  This means that the endpoint will not be at 7.  Using the Ka for benzoic acid estimate the approximate pH of the endpoint and determine an appropriate indicator for you to use. 
4. Ask your teacher for the appropriate indicator.  If the one you request is not available be prepared with 2 other alternate choices!
5. You will have to make up a solution of indicator for your use.  Either water or alcohol will be needed as a solvent.
6. Dissolve the benzoic acid in a minimum amount of water in an Erlenmeyer flask and add enough of your indicator to colour the solution.
7. Titrate the benzoic acid solution with your KOH.
8. Repeat the titration with fresh samples of benzoic acid twice more. 
9. Calculate the average molarity of the KOH

Part 3.  Titration of the weak acid against the known KOH solution
1. Get a sample of either formic or ethanoic acid from your teacher.
2. You are again titrating a weak acid against a strong base.  The endpoint will not the 7 again but it will also not be the same as the benzoic acid endpoint.  Re-estimate the endpoint using the Ka of either the formic or ethanoic acid to determine an appropriate indicator to use.
3. Using a pipette, accurately transfer some of your acid sample to a clean Erlenmeyer flask.  Record the amount of acid transferred.
4. Titrate your sample of weak acid.
5. Repeat with two more samples of your weak acid.
6. Calculate the average molarity of your weak acid.

Data Table:
Part 1
1.    Mass of KOH used: ____________ grams
2.    Volume of volumetric flask: ___________ mL

Part 2
3.    Ka of benzoic acid: ________________    Kb of benzoic acid:_______________
       pKa of benzoic acid: _______________   pKb of benzoic acid: ______________
       Indicators:  Choice #1 ______________
                        Choice #2 ______________
                        Choice #3 ______________
                        Choice #4 ______________


Trial #1
Trial #2
Trial #3
4.    Mass of Benzoic acid used: g
g
g
5.     Volume of KOH solution used: mL
mL
mL
6.    Calculated molarity of the KOH solution: M
M
M

7.    Average molarity of the KOH solution: _________

Part 3
8.    Acid used: ______________________
9.    Ka of acid: _____________________    Kb of acid: ___________
10.    pKa of acid: ____________________    pKb of acid: _________

11.    Approximate pH of the final solution:  __________
         Indicators:  Choice #1 ______________
                             Choice #2 ______________
                             Choice #3 ______________
                             Choice #4 ______________


Trial #1
Trial #2
Trial #3
12.   Volume of  acid used: mL
mL
mL
13.   Volume of KOH solution used: mL
mL
mL
14.   Calculated molarity of the acid: M
M
M

15.   Average molarity of your sample acid: ___________