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Microsoft Word - EXAMPLE LABORATORY MEMO_v2_Whelton
To: Andrew Whelton, Ph.D., Brian Merkersen; Dept. Civil Engineering, Univ. of South Alabama
From: John Snow, Jiminy Cricket, Unji Punji; CE 374 students
Date: Fe
uary 19, 2013
Subject: Results of Water pH and Alkalinity Characterization of Unknown Water Sample
Greetings Dr. Whelton:
Below we have provided a summary of the laboratory experiment conducted on Fe
uary 9, 2013.
Please feel free to contact us if you have any questions.
Regards,
John, Jiminy, and Unji
Summary of Water pH and Alkalinity Characterization of the Unknown Water Sample
Introduction. The purpose of this experiment was to learn and apply wet chemistry techniques and
quantify the alkalinity concentration of a water sample of unknown origin. This water sample was
provided by the Instructor. Water quality characterization was conducted on Fe
uary 9, 2013 from 2:00
PM –– 3:14 PM in the Shelby Hall Environmental Engineering Laboratory.
The alkalinity concentration of a water (commonly reported as mg/L as CaCO3) represents the
uffering capacity of that water. More specifically, alkalinity enables waters to resist water pH
eductions when acid is added or formed in situ. Phenolphthalein alkalinity can be quantified by
determining the amount of acid required to reduce the water pH above 8.3 to 8.3. Total alkalinity is a
measure of the total quantity of acid required to reduce a water’’s pH to 4.3. By knowing our acid
normality and the volume of acid added to a water for targeted water pH reduction, phenolphthalein
and total alkalinity levels can be determined. Specific objectives of this work were to: (1) titrate the
unknown water sample to a pH of 8.3 and then 4.3 using a sulfuric acid solution, (2) calculate the
phenolphthalein alkalinity and total alkalinity of that water, and (3) describe the significance of these
esults.
Methodology. A 300 mL water sample was provided by the Instructor for analysis. At the end of the
class period while students were cleaning up, the instructor stated that unknown sample was created by
adding 4.67 g NaHCO3 to 1 L of water. To determine alkalinity levels, five drops of phenolphthalein
indicator solution were added to the solution on a stirplate. Sulfuric acid XXXXXXXXXXN) was added by
titration until the solution became colorless (at pH 8.3). Phenolphthalein indicator solution added a pink
color to the solution. After a water pH value of 8.3 was achieved, additional sulfuric acid was added until
a water pH of 4.3 was achieved. The volume of titrant added to achieve each end point was recorded.
Calculations were conducted using Equation 1 to determine phenolphthalein and total alkalinity
concentration of the water sample. An Accumet pH meter was used to monitor pH changes and this
instrument was cali
ated to pH values of 4.01, 7.0, and 10.01 before titration commenced.
Alkalinity, mg/L as CaCO3 = (mL titrant)(titrant normality)(50,000) / (mL sample) Equation 1
Results and Discussion. The initial water pH was 9.4 and the exact alkalinity concentration of the wate
(phenolphthalein and total) was not determined by titration. More than 300 mL of titrant was added to
the solution during the experiment and this volume addition was unexpected since only 300 mL of initial
sample was present. After addition of 300 mL of titrant, water pH was only 8.4. Using the 300 mL titrant
esult, the theoretical phenolphthalein alkalinity concentration of the water sample was calculated to be
1,250 mg/L as CaCO3. Since the water pH had not reached 8.3, this value accounts for only the
phenolphthalein alkalinity of the water. Total alkalinity concentration of the water sample would have
een significantly greater than the phenolphthalein alkalinity concentration by definition.
Since the Instructor described how the water was created at the end of class (4.67 g NaHCO3 to
1 L of water), the theoretical total alkalinity level of that water was calculated. One mole of NaHCO3
addition to the water resulted in one mole of HCO3 addition to the water. Applying molecular weight
and equivalent weight values for NaHCO3 and CaCO3 (Table 1), calculations revealed that the unknown
water sample contained a total alkalinity level of 2,780 mg/L as CaCO3. Applying Equation 1 again, a total
of 667 mL of titrant was found to be required to remove all of the alkalinity (2,780 mg/L as CaCO3) and
educe pH to 4.3. Calculation steps included (1) determination of the molar concentration of NaHCO3 in
the water XXXXXXXXXXmoles/L), then (2) conversion of that value to mg/L as CaCO3. In retrospect, successful
quantification of the alkalinity level could have been achieved by diluting the initial water sample with
deionized water and/or using a stronger sulfuric acid solution (> 0.025 N). Since the initial level was
unknown, this result could not be avoided.
Table 1. Values Applied to Calculate the Unknown Water’’s Alkalinity Concentration
Compound
Name
Mole Wt.,
g/mole Equiv.
Equiv. Wt.,
g/equiv
NaHCO XXXXXXXXXX
CaCO XXXXXXXXXX
A review of the US Environmental Protection Agency website indicated that typical drinking
water alkalinity levels range from 30 to 200 mg/L as CaCO3. The CE 370 Environmental Engineering
textbook also described that natural water alkalinity is typically less than 200 mg/L as CaCO3. Based on
this evidence, the water sample analyzed in this experiment was not likely a drinking water or natural
water (i.e., river, lake, stream). It is possible this water could be a waste of an industrial process.
Conclusion. A water sample of unknown origin was characterized for its phenolphthalein alkalinity and
total alkalinity concentration by titration. Titration with sulfuric acid was ca
ied out. Titration results
showed that this water was highly buffered, resisting water pH reduction. Experimental testing
demonstrated that neither the phenolphthalein nor total alkalinity levels could be determined because
all titrant was used in the laboratory. Even after 300 mL of titrant was added to 300 mL of initial wate
sample, the water pH remained above 8.3.
The theoretical total alkalinity concentration of the unknown water sample was 2,780 mg/L as
CaCO3. Using this theoretical value, a total of 667 mL of 0.025 N sulfuric acid solution was needed to
educe pH to 4.3. If the concentration of the water needs to be determined experimentally, future
students should apply a stronger sulfuric acid titrant (> 0.025N) and/or dilute the initial water sample (1
to 100 ratio). The alkalinity concentration of the unknown water was not typical of drinking water o
natural waters (i.e., river, lake, stream). The source of the water sample should be investigated.
NOTE TO STUDENTS:
No series of Tables or Figures were necessary. Not all data requires a table/figure.
Writing was in third person
Many active ve
s were applied
Few prepositional phrases were applied
Details, details, details! Superscripts and subscripts were used, NO spelling or punctuation mistakes
Results were compared to the literature (EPA and textbook) for context
Even though the end points were not reached (pH 8.3 and 4.3) the results could still be described
Table and figure titles need to be descriptive; Label Tables on the top figures on the bottom