Date __________
Lab Time ______
Name ___________________________
Coke Floats (Or Does It?)
Objective
Scientific measurements will be introduced using common soft drinks as examples. Studentcollected data will be pooled leading to a discussion of accuracy and precision.
Background
The measurements physical scientists make are often used in calculations to obtain other
related quantities. A number of common devices enable us to make simple measurements of
a substance’s properties: the meter stick measures length, the graduated cylinder measures
volume, the balance measures mass and the thermometer measures temperature. These
physical measurements allow for characterization and possible identification of a substance.
A Physical property that is a characteristic of substance include melting point, boiling point,
and density. All chemically pure water samples, for example, melt at 0 oC, boil at 100 oC
under one atmosphere pressure, and have a density of approximately 1.0 g/mL.
If a particular measurement is repeated, precisely the same result is usually not obtained
because each measurement is subject to some type of experimental error. Suppose you
perform a series of identical measurements of a quantity. The term precision (P) refers to
the closeness of a set of values to each other which were obtained from identical
measurements of the same quantity. Accuracy (A) is a related term that refers to the
closeness of a single measurement to its true or excepted value. Look at the “dart boards”
below as examples.
High A
Low P
Low A
High P
High A
High P
Low A
Low P
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Coke Floats (Or Does It?)
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Date __________
Lab Time ______
Name ___________________________
Materials needed
2 - 100 mL graduated cylinders
balance
pitcher of sweetened lemonade @ room temp.
12-oz can of soda @ room temp.
12-oz can of Diet soda @ room temp.
Ruler
Procedure
Part I – Regular Soda Measurements
Density:
1.
Using an electronic balance, measure the mass of an empty 100 mL graduated cylinder and record the mass
on your data sheet.
2.
Add approximately 75 mL of one of the regular soft drink to the empty graduated cylinder. Read the actual
volume of the soft drink as accurately as possible. Record the volume of the soft drink on your data sheet.
{When reading volumes using graduated devices, accurate and precise values are obtained by reading at
eye level and using the bottom of the meniscus}.
3.
Using the same electronic balance you used in Step 1, measure the mass of the soft drink plus the
graduated cylinder. Record the mass on your report sheet.
4.
Calculate the mass of just the volume of soft drink and record.
5.
Using the expression below, calculate the mass density of the soft drink and record.
{Mass Density is computed by dividing the mass of a substance by the volume it occupies. This relationship
is expressed mathematically as}
mass density =
mass
volume
or
ρ=
m
V
Verifying the Manufacture’s Claims:
6.
Using your graduated cylinder, determine and record the total volume of soft drink in the can by repeating
Step 2 until all the soda in the can has been measured.
7.
Record the total volume of the soda as listed on the side of the can.
8.
Calculate (do not measure) the total mass of the soft drink using the soda’s mass density from Step 5 and
your result from Step 6.
9.
Determine the % Sugar in the can of soda by dividing the amount of sugar per serving (as listed on the
side of the can) by your total calculated mass from Step 8.
10. Using the graph on page 4, determine the % sugar in your sample of soft drink and record.
{Draw a horizontal line at the same density reading as your calculated density. At the point where it
crosses the Regression Line, draw a vertical line downward. The point where it touches the bottom axis will
represent the % sugar in your soft drink.}
11. One member of your group go to the board and write your values for total volume and density under the
appropriate columns for class analysis.
Part II – Diet Soda Measurements
Repeat the entire procedure in Part I using a diet soda.
Part III – Unknown Measurements
Repeat Steps 1 – 6 of the procedure in Part I using an unknown sample of lemonade.
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Coke Floats (Or Does It?)
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Date __________
Lab Time ______
Name ___________________________
Report Sheet – Data Analysis
Part I - Regular Soda Measurements
Mass of 100 mL graduated cylinder empty
__________ g
Combined Mass of ~75 mL of soft drink & 100 mL graduated cylinder
__________ g
Mass of ~75 mL of soft drink only
_______________ g
Actual Observed Volume of soft drink in cylinder
_______________ mL
Density of soft drink
_______________ g/mL
Total measured volume of soft drink in can
_______________ mL
* Total volume of soft drink as listed on side of can
_______________ mL
Total calculated mass of soft drink in can
_______________ g
* Percent sugar in soft drink (Manufacturer’s Claim)
________________ %
Percent sugar in soft drink (from graph)
________________ %
Calculations:
Part II - Diet Soda Measurements
Mass of 100 mL graduated cylinder empty
__________ g
Combined Mass of ~75 mL of soft drink & 100 mL graduated cylinder
__________ g
Mass of ~75 mL of diet soft drink only
_______________ g
Actual Observed Volume of diet soft drink in cylinder
_______________ mL
Density of diet soft drink
_______________ g/mL
Total measured volume of diet soft drink in can
_______________ mL
* Total volume of soft drink as listed on side of can
_______________ mL
Total calculated mass of soft drink in can
_______________ g
* Percent sugar in diet soft drink (Manufacturer’s Claim)
________________ %
Percent sugar in diet soft drink (from graph)
________________ %
Calculations:
_____________________
Coke Floats (Or Does It?)
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Date __________
Lab Time ______
Name ___________________________
Part III - Unknown Measurements
Mass of 100 mL graduated cylinder empty
__________ g
Combined Mass of ~75 mL of unknown & 100 mL graduated cylinder
__________ g
Mass of ~75 mL of unknown sample only
_______________ g
Actual Observed Volume of unknown sample in cylinder
_______________ mL
Density of unknown sample
_______________ g/mL
Percent sugar in unknown sample (from graph)
________________ %
Calculations:
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Coke Floats (Or Does It?)
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Date __________
Lab Time ______
Name ___________________________
Post-lab questions:
1. Using both the Soda and Diet Soda, compare the % sugar you calculated and your measurements
for the total volume for each can against the manufacturer’s claim (see label on can).
What is your percent error in the total volume for each case?
2. Suppose a certain individual can have 1 glass of sweetened lemonade a day without getting ill so
long as the sugar content is less than 5 %. Would a glass of lemonade from your unknown sample
be safe for them to drink? Why?
3. Why was it necessary for the soft drinks to be open at room temperature?
4. Copy the Results of the Classroom from the board below and then calculate the average values of
total measured volume and calculated mass density for both the regular and diet soft drinks.
Comment on the accuracy and precision in the data.
Regular Soft Drink
Diet Soft Drink
5. Why can’t you make any statements about the precision of your individual data?
6. What specific sources of error (do not include human error) in this experiment could have
produced inaccurate results?
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Coke Floats (Or Does It?)
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Date __________
Lab Time ______
Name ___________________________
Summary/Conclusions:
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Coke Floats (Or Does It?)
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