Ex 5
Important notes
• Naming files
• Must use the excel templates posted on
the course website
• Data Section of the Lab Report
• Lab 5 Experiment and Calculations
Naming files
• Last name first name sect# lab #
• So, if you are in Tuesday’s lab section,
your name was David Ortiz and you are
attempting to upload lab report 5 you
should upload two files named
OrtizDavidsect2lab5.doc
and
OrtizDavidsect2lab5.xls
Ex 5
• Preparation of 0.10 M NaOH solution
• Standardization of NaOH by titration with
potassium hydrogen phthalate (KHP)
• Titration of a diluted commercial vinegar
solution.
• Propagate Uncertainty
• Use data from another pair of classmates to
determine if the acetic acid concentrations of red
and white vinegars are significantly different.
Preparation of NaOH
• 6 mL of 50 % NaOH in 1 L
• No CO2 because it precipitates as Na2CO3
• Boiled water
Standardization of NaOH solution
• Weigh 0.4-0.7 g KHP and quantitatively
transfer to an Erlenmeyer flask.
• this about 2.5 mmol
• Therefore, about 25 mL of 0.1 M NaOH
will be required to titrate this weak acid
• Phenolphthalein indictor (pH 8-10)
• Estimate the pH at the equivalence point
pH = 9
• Do five samples.
Standardization of NaOH
K b1


2
HP  OH  P  H 2O
1mol
(massKHP )(
)
204.23 g
[ NaOH ] 
Veq
Take average of the [NaOH] calculated from the each of the five trials
Vinegar titration
Concentration of HA in Vinegar
25 mL
Diluted vinegar
from pipet
Buret full of NaOH
25 mL
Vinegar
from pipet
Erylmeyer flask
250 mL
flask
Concentration of
acetic acid (HA) in vinegar


HA  OH  A  H 2O
[ NaOH ](Veq ( ave) ) V flask
[ HA] 
(
)
Vdil.vinegerpipeted
Vvinegar
Uncertainty in [HA]vinegar
[ NaOH ](Veq ( ave) ) V flask
[ HA] 
(
)
Vdil.vinegerpipeted
Vvinegar
s[NaOH] = ±95 % CI
sVeq(ave) = ±95 % CI
sV(dil vinegar) = ±0.03 mL
sV(flask) = ±0.12 mL
sVvinegar = ±0.03 mL
Uncertainty in [HA]Vinegar
[ NaOH ](Veq ( ave) ) V flask
[ HA] 
(
)
Vdil.vinegerpipeted
Vvinegar
Multiplication and division rule: sum of the squares
of the relative uncertainties are additive.
(
sHA( vin)
[ HAvin ]
) (
2
s[ NaOH ]
[ NaOH ]
) (
2
sVeq
Veq
) (
2
sVflask
V flask
) (
2
sVpipet
Vdil.vinegar
) (
2
sVpipet
Vorig.vineger
)2
Are the [HA] in red and white
vinegar statistically different?
• Switch data with another set of students so that
you have one set of data for red and another for
white.
• You need to get both the standardization data
and the vinegar data from your neighbors
• Perform t-test to compare the means to the 95 %
CL; (N=5) for both sets
• Perform F-test to see witch version of the t-test
you need to use.