Acid Base Titration Lab
Caution: Acids and bases can blind you. Wear your goggles at all times during this lab.
Goal: to determine how many ml of 12 M HCl Mr. Samson used in making 500 ml of solution.
1.
Take your 250 ml beaker to the front of the class room and obtain exactly 10 ml of HCl
from Mr. Samson.
2.
Add 50 ml of distilled H2O to the acid in your beaker and also add a few drops of
bromothymol blue indicator. This indicator will change from yellow to blue when the
solution changes from acidic to basic, and will turn green near the equivalence point.
3.
Place your beaker of acid solution under your burette and clamp the pH probe so that its
tip is just above the bottom of the beaker.
This burette contains a 0.1 M solution of NaOH.
4.
Click the “collect” button and enter a value of 0.0 ml. (you do not type “ml”)
5.
Add 0.5 ml of NaOH solution to your acid solution and swirl the beaker.
6.
Record your data by clicking the “collect” button and entering the exact amount of NaOH
that you decanted from your burette.
7.
Add another 0.5 ml of NaOH and repeat procedure 5, recording the total volume of
decanted NaOH.
8.
Continue this process, adding 0.5 ml NaOH each time.
9.
When the pH reaches a value of 3.0, begin adding NaOH 0.1 ml at a time.
10.
When the pH reaches a value of 5.0, begin adding NaOH one drop at a time
11.
When the pH reaches a value of 9.0, begin adding NaOH 0.1 ml at a time.
12.
When the pH reaches a value of 11.0, begin adding NaOH 0.5 ml at a time.
Continue this process until you have decanted 15 ml of NaOH.
10.
Use your graph and data table to answer all the questions on your question sheet.
Acid Base Titration Lab
1.
Name ___________________________
What was the pH of the solution in your beaker at the start of the titration? __________
What was the pH of the solution in your beaker at the end of the titration? __________
2.
In the space below, draw a sketch of the graph produced by this titration.
3.
How many ml of 0.1 M NaOH solution did it take to reach a pH of 7? _____________
4.
When the pH was 7, the number of moles of NaOH added to the solution was the same as
the number of H+ ions in the acid. If you find the number of moles of OH ions you added
to the solution, you can infer that this is also the number of H+ ions in the unknown.
Calculate the number of moles of NaOH you added to the solution.
(hint: start your calculation with the volume of NaOH you added)
Moles of NaOH: ____________
Moles of HCl in unkown solution: ____________
5.
Calculate the molarity of the HCl solution, given the fact that you started with 10 ml.
Molarity of HCl solution: _________
6.
Use the molarity value from #5 to find the pH of the unknown solution: _____________
7.
Now that you know the molarity of the acid solution, calculate the number of ml of 12 M
HCl that was added to a 500 ml volumetric flask to prepare this solution: __________