ACID – BASE TITRATION
PURPOSE: The purpose of the laboratory is to determine the molarity of solution of KOH by titrating with
a standard solution of HCl.
EQUIPMENT;
50 mL buret
buret stand
buret clamp
Erlenmeyer flask (2)
graduated cylinder – 25 mL
beakers –100 or 250 mL (2)
dropper pipet
safety goggles
lab apron
MATERIALS:
0.105 M HCl (standard solution)
NaOH (concentration unknown)
white vinegar
water
phenolphthalein
SAFTEY:
Follow all precautions for working with acids and bases. Wear safety goggles and aprons at all times.
PROCEDURE:
Part A
Determination the concentration of NaOH using a 0.105 M standard solution of HCl
1.
Rinse the buret with small amounts of NaOH solution. Fill the buret with NaOH solution , make sure
that there are no bubbles in the buret, including the tip. Place the buret in the clamp.
2.
Add 10.0 mL of HCl solution to an Erlenmeyer flask. Rinse with distilled water. Add two drops of
phenolphthalein to the flask.
3.
Record the buret reading and titrate the acid with the NaOH solution until it turns a pale pink that lasts
30 seconds. Be careful not to over titrate. Record the reading of the buret in your data table.
4.
Repeat steps 3 & 4 with a second and third Erlenmeyer flask.
5.
Calculate the molarity of the NaOH using MaVa = MbVb. Be sure to write a balanced equation. Show
all calculations.
Part B
Determination of the molarity of white vinegar with NaOH.
1.
Add 10.0 mL of vinegar to a clean Erlenmeyer flask. Rinse with distilled water. Add two drops of
phenolphthalein to the flask.
2.
Record the buret reading and titrate to the first pink color that lasts for 30 seconds. Be careful no to
over titrate. Record the final reading of your buret.(Note this will not be a pale pink)
3.
Repeat steps 1 & 2 with another flask.
4.
Calculate the molarity of the acid using the molarity of the NaOH. Be sure to average your results.
5.
Use the formula MaVa = MbVb for your calculations. Write a balanced equation for the neutralization
of acetic acid (vinegar) with NaOH. Show all calculations
DATA TABLE
SAMPLE #
1
MA
VA
2
3
Vinegar
1
2
3
CALCULATIONS
MB
VB
CONCLUSIONS AND QUESTIONS
1. How reproducible were the results of the two trials?
2.
Define these terms: Standard solution; titration; end point; volumetric analysis; gravimetric analysis.
3.
If 30.0 mL of 0.500 M NaOH is needed to neutralize 15.0 mL of H 2SO4 of unknown concentration.
What is the molarity of the acid?
4.
What would happen to the results if you failed to rinse the flask well and it contained soap residue?
5.
What would happen to your results if a large bubble passed through the buret?
6. What would happen to your results if you rinsed the acid into the flask with more water than directed?