College Prep Chemistry
Core Lab #12
50 points
Determination of the Molarity of a Base by Titration
Objective: To determine the molarity of NaOH by titration.
Introduction and Pre-Lab: Define the terms: titration, indicator, and neutralization.
Equipment:
250 mL Erlenmyer Flask
Beaker
Procedure:
Funnel
Buret Clamp
Buret
Distilled Water bottle
To set up the flask:
a. Obtain approximately 0.50 grams of KHP. Record the exact mass in Table 1.
b. Place the KHP into a clean 250 mL Erlenmeyer flask and add approximately 50.0 mL
of distilled water. Swirl the solution in order to get the maximum amount of solid to
dissolve. (All of the KHP may not be dissolved at the start of the experiment but
more will go into the solution as the experiment progresses.)
[Question: If solid is left behind because not all of the KHP Acid dissolves what
type of solution is it?
Saturated, unsaturated, or supersaturated?]
c. Place 1 drop of phenolphthalein into the flask containing the acid. Record any color
observations in Table 2.
To set up the buret:
a. Clean the buret:
a. Rinse the buret with deionized water 3 times in to a waste beaker.
b. Rinse the buret with the sodium hydroxide solution 3 times.
b. Using the 100 mL beaker, obtain a sample of NaOH(aq) from the front bench. Fill the
clean buret with just over 50 mL of NaOH(aq). (Note: you are filling the buret to the
0.00 mark at the top.) Run the buret to remove any air bubbles. Record the initial
volume of NaOH in the table. You must read the buret to the nearest 0.01mL.
c. Begin the titration (add the NaOH solution from the buret into the flask containing
the acid). The titration will be completed when the solution remains a pale pink
color. Be sure to swirl the Erlenmeyer occasionally so the solution can mix. Be very
careful and adds drops very slowly towards the end of the titration.
d. Show the colored solution to the teacher to see if the pink color is light enough. If it
is not, you
must redo the titration.
e. When the titration is complete, record the final volume of the NaOH in the buret.
f.
g.
h.
i.
Observe and record the color of the phenolphthalein a base.
Repeat steps 2 through 6 two more times for a total of three trials.
Then, calculate the change in volume for each trial.
Lastly, rinse all glassware and the lab bench with water. The buret should be rinsed
3 times then hung upside down with the valve left open to dry.
Data:
Table 1: ______________________________
Trial 1
Trial 2
Trial 3
Mass of KHP
Initial Volume of
NaOH
in Buret
Final Volume of NaOH
in Buret
Change in Volume of
NaOH in Buret
Table 2: Observations of Phenolphthalein in an Acid and a Base
Observations
Phenolphthalein in an Acid
Phenolphthalein in a Base
Analysis :
1. Using the median value in your data, determine the number of moles of KHP Acid used
in the experiment.
2. Determine the number of moles of OH- (NaOH) that were used to neutralize the H+ (KHP
Acid).
3. Determine the molarity of the NaOH solution. (Experimental value)
4. Collect class data on a stem and leaf plot.
5. Complete statistics for the molarity of the NaOH solution from the stem and leaf (n,
min, max, med, σ).
6. Calculate the percent error for your group.
Results:



Identify and report the class value and experimental value for the molarity of sodium
hydroxide.
Report percent error
Sentence format
Conclusion:

See rubric for guidelines
College Prep Chemistry
Core Lab #12
50 points
Determination of the Molarity of a Base by Titration Rubric
Format
6 points
 Written in pencil (1)
 Table of Contents up to date (1)
 Underline appropriate titles (1)
 Use appropriate units throughout and significant digits (1)
 Title all tables, graph, and figures (1)
 Tables and graphs are drawn with straight edge (1)
Introduction and Pre-Lab
3 points
 Restate the objective and incorporate how the objective was met by performing this lab
(3)
o Discuss the process of titration.
o Link any appropriate definitions to the lab.
 Pre lab terms defined correctly
Data /Analysis
16 points
 Table 1 and 2 completed appropriately (5)
o Volumes observed and recorded correctly from the buret
 Calculations (5)
o Work shown
o Correct answer
o Significant figures used
 Stem and Leaf (2)
o Scale, key
 Summary data table (2)
o n, min, max, med, σ
 Percent Error (2)
o Formula, substitution, and answer
Results
5 points
 Identify and report the class value and experimental value for the molarity of sodium
hydroxide.
 Report percent error
 Sentence format
Conclusion
7 points
 Address the objective. Support your answer with lab data and results (2)
 Identify 2 sources of error and the effect they would have on the experiment (2)
o Source of error
o Effect on data
o Effect on result
 Conclusion quality: well organized and cohesive and contains no
mechanical/grammatical errors. (3)
o Well organized and cohesive but contains grammatical or mechanic (2)
o Somewhat organized but does not contain any errors (2)
o Somewhat organized with some errors (1)
o Disorganized with errors (0)