Biology of the Cell (Biol 1021)
Conversions and Introduction to Lab Equipment
Lab 1
Introduction
Experimental observations can be expressed either qualitatively or quantitatively. Qualitative
observations describe the characteristics of the system in non-numerical terms. “The apple is red”
is an example. Qualitative observations are sometimes sufficient in describing a phenomenon or system
and when comparing two things. Quantitative observations involve a measurement or a count.
“The apple weighs 525 grams” is a quantitative observation. Quantitative observations are more
objective, since they do not depend on the observer’s methods method of measurement or cultural
history, and are equally understood anywhere in the world.
To understand the difference, try to buy two cans of red paint at two different stores. Matching
your concept of red to that of the salesman can be extremely difficult. Now add to the equation trying to
buy the paint in a store where the salesman doesn’t speak English. However, both of you probably know
precisely what is meant by “2” fingers held up, regardless of language or culture.
Ideally the system of measure that we use should also be objective. The French tried to achieve
this objectivity and did away with their old system of units of measure and established one based on
physical parameters that would have the same values no matter when or where they were measured.
We refer to this as the metric system of measurement (also the Systeme International or SI).
Conversion between metric and American system is fairly easy. The creation of a conversion
factor allows for the switch between the two systems. A conversion factor is a ratio that consists of a
numerator and a denominator. The numerator is what you are converting TO and the denominator is
what you are converting FROM. If the appropriate conversion factor isn’t available, you can ‘string
together’ several conversion factors to get the value that you are looking for.
Let us try an example: How many inches are there in 3 meters?
1) We are ultimately converting TO inches FROM meters using multiple conversion factors (CF). Using
Table 1 at the end of this ‘lab manual’ we know that 1 m is 3.28 ft. We also should know that 1 ft is
12 inches. We can now create our various CF.
2) CF1 is converting FROM meters (denominator) TO feet (numerator) and would be:
3.28 feet
1m
3) CF2 is converting FROM feet (denominator) TO inches (numerator) and would be:
12 inches
1 foot
4) ? in = 3 m x CF1 x CF2 or
3m x 3.28 ft x 12 in
1m
1 ft
5) The meter in the numerator and denominator can be canceled; the same is true of feet. This leaves
you with:
3m x 3.28 ft x 12 in
1m
1 ft
3 x 3.28 x 12 inches = 118.08 inches
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Biology of the Cell (Biol 1021)
Conversions and Introduction to Lab Equipment
Lab 1
The goal is to be able to cancel out all of the units with the exception of what we are looking for, i.e.
inches.
Another advantage of the metric system is that the units are based on multiple of tens. There is
an established set of prefixes that represent the powers of ten. These can be used to create conversion
factors as above. Table 2 at the end of this ‘lab manual’ lists some commonly used prefixes. The
prefixes may be applied to meters, liters or grams.
Let us try an example. How many liters is 3325 milliliters?
1) Determine the powers of the measure you are converting between from their prefixes. In our
examples, the power of milliliters is –3. Since liter has no prefix, its power is 0.
2) Subtract the power of the measure you are converting TO (liters) from the power of the measure you
are converting FROM (milliliters). In our example: The equation is (-3) – 0 = -3
3) The difference is the power of ten of the converted measure. So in our example, 3325 ml = 3325 x
10-3 L or 3.325 L
Since the power of ten is negative, we can simplify the answer by moving the decimal that many spaces
to the left. If there had not been enough spaces to the left, we could fill in with zeros. Had the power
been positive, we would move the decimal point to the right and add zeros as needed.
You will be able to practice some of these conversions factors in your homework assignment that
is due at the start of the next lab period. Use whichever method to perform a conversion that is easiest
for you and show your work. Be very familiar with these methods as they will show up on your exams.
Laboratory Procedure
To give you experience in working with the metric units of measures in the laboratory setting, you will
perform exercises in which you will determine the density of water, the density or vegetable oil or a
sucrose solution as well as some other objects. The density of a substance is its mass per unit
volume. Density is determined by recording the masses of increasingly larger volumes of the
substance. Once the data is collected, a graph of MASS vs. VOLUME is platted and the slope of the
straight line that passes closest to the most points is calculated. This slope is the density of the
substance.
Exercise 1 – Determination of the density of water
1) Find on your bench the following items: a pipette bulb, a 5 mL pipette, a 10 mL pipette and a weighing
boat.
2) Turn on the automatic balance at your site, and if it reads other than 0, press the tare button so that the
scale will read 0.
3) Place the weighing boat on the pan of the automatic balance and determine the mass. Record this
value on your worksheet.
4) Now press the tare button and note that the balance again reads 0. The balance automatically
“subtracts” the mass of the weighing boat from future readings in a process of taring.
5) Place the pipette bulb on the end of the 5 mL pipette and measure 1 ml of distilled water into the
weighing boat. NOTE: The 5 ml pipette is capable of holding 5 ml of liquid; the pipette is divided into
1/10th increments. Therefore 1 ml would consist of 10 small lines. Record the mass of the water on
your worksheet.
6) Leaving the weigh boat with the 1 ml of water on the scale, use the same pipette to place an additional 2
mL of water into the boat (total 3 mL). Record the mass of the water on your worksheet.
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Biology of the Cell (Biol 1021)
Conversions and Introduction to Lab Equipment
Lab 1
7) Repeat Step 6 with an additional 2 mL of water (total 5 mL). Record the mass of the water on your
worksheet.
8) Repeat step 6 with an additional 5 ml of water (total 10 mL). Record the mass of the water on your
worksheet.
9) Repeat step 6 using the 10 mL pipette to add 10 mL of water (total 20 ml). Record the mass of the
water on your worksheet.
10) Empty the water from the weigh boat, dry and repeat Steps 3 through 9 an additional 2 times (a total of
3 measurements per volume). Each run through of the experiment is called a trial or replicate. As you
increase the number of trials you can decrease the level of error.
11) Using the data from your worksheet, draw a graph from your data using the volumes as your
independent variable (the variable you measured with the least error) plotted along the horizontal axis
and the masses as your dependent variable (the variable you determined as an unknown with error)
along the vertical axis. You will have 3 points for each volume.
4
Mass (g)
3
2
Rise
1
Run
0
0
1
2
3
Volume (ml)
12) Draw a straight line so that it passes through or near most of the points on your graph. This line is
known as the best-fit line. DO NOT connect the dots. Try to have as many points above the line as
below as this will insure a good representation of the data.
13) Calculate the slope of this line – the slope of this line is equal to the density of water. Remember, a
volume of 0 has no mass, so you know that the line must pass through the origin as one of the points on
your graph. The slope can be calculated by choosing 2 points on the line that are easy to determine the
coordinates. Label them as point 1 and point 2. Record the location of the points as (x1,y1) for point 1
and (x2,y2) for point 2. The slope is then rise over run or :
y2 – y1
x2 – x1
Exercise 2 - Determination of the density of an unknown liquid.
Repeat the steps from Exercise 1 to determine the density of either vegetable oil or a sucrose solution
obtained from the instructor. Record the sample name on your worksheet. Only complete one trial for
this exercise. You will graph the data on the graph for water density. This way you will be able to
compare the density of this substance compared to the density of water.
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Biology of the Cell (Biol 1021)
Conversions and Introduction to Lab Equipment
Lab 1
Exercise 3 – Determination of the density of a solid.
The density of a solid can be determined if both the volume and the mass is known. For solids
with regular shapes (spheres, cylinders, cubes etc) the volume can de calculated directly using
measurements obtained from the object and the known geometric formulae. For irregularly shaped solid
objects, the volume can de determined by displacement of a liquid. The volume of water displaced will
indicate the volume of the irregular shaped object. You are responsible for determining the density of an
irregular shaped object that you get from the instructor.
1) Obtain a 25 or 100 mL graduated cylinder and the solid object for which you are to determine the
density from the instructor.
2) Fill the graduated cylinder part way with water and record the volume. Remember to read the
volume at the bottom of the meniscus at the surface of the water.
3) Determine the mass of the object on the scale. DO this first so as not to have to worry about a
wet object.
4) Drop the solid into the graduated cylinder. Read the new volume of the water. The volume of the
solid is the difference between this volume and the previous one.
Exercise 4 – Determination of the size of a molecule (Sources:
http://www.stkate.edu/physics/phys100/MoleculeSize.html; http://www.chemheritage.org/EducationalServices/pharm/antibiot/activity/size.htm;
http://www.arborsci.com/Data_Sheets/C4-1000_DS.pdf).
When dispensed on the surface of water, oleic acid, which is a liquid, will spread out on the surface
to form a layer. Oleic acid has the formula C18H34O2 and the structure below:
One end of the molecule is hydrophilic (attracted to water) and the other is hydrophobic. When oleic
acid is dropped on the surface of water, the molecules stand up on end, like people standing in a
crowd. The molecules form a monolayer – a layer that is one molecule thick. We will assume that it
forms a monolayer, a layer that is a single molecule thick. By finding the area of the layer and the
volume of the layer we can perform a simple calculation to find its thickness.
Procedure
1. Before you do anything, you'll need to know how much oleic acid is in one drop. Take the given
mixture and select one person in your lab group that will do the dropping. This is important that you
get some consistency. If you have several people make drops, the sizes will probably vary. Use the
eye dropper and count the number of drops to make 1 ml in your graduated cylinder. The volume of
one drop is merely:
Volume of 1 drop of oleic acid solution = 1 ml of oleic acid solution/number of drops in 1 ml
You can do this a few times to confirm your value. Find the volume of one drop.
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Biology of the Cell (Biol 1021)
Conversions and Introduction to Lab Equipment
Lab 1
2. Your instructor has mixed the solution of 5 ml of oleic acid per 1000 cm3 of denatured ethanol. In this
lab, oleic acid is provided in a solution of ethanol. This is done to allow only a very small volume of
acid to be put on the water surface. Otherwise, you’d need a very, very large tray to do the lab.
Thus, each drop of solution contains 1/200th of the volume of a drop of oil. i.e.; the volume of oil in one
drop is the volume of one drop divided by 200.
e.g. If there are 50 drops in 1 ml, then each drop has a volume of 1 / 50 ml or 1 / 50 cm3. The amount of
oleic acid (oil) in one drop is then:
1 / 50 X 1 / 200 = 1 / 10,000 = .0001 cm3
3. Place the water in the tray, about 1 to 2 cm deep. Lightly spread the Lycopodium powder over the
water. This step requires a soft touch.
4. Have your lab partner who does the drops actually drop one little drop onto the surface. The
yellowish powder will recede rather quickly. Someone has to measure the diameter of the oil slick.
Do these actions quickly as there may be some recoil, i.e., the slick may even oscillate. Record your
results, wash out the tray, and repeat Steps 3 & 4 two more times.
5. The area of the slick is merely r2 so we can find the volume of the oil slick as thickness X area:
Volume = r2 X h
6. Find the thickness or length of the molecule or basically of the oil slick.
7. List LIMITATIONS to the experiment. What assumptions, valid or not, are being made to conduct
this experiment?
8. Record your data clearly and show your analysis.
During the next class period, your value for oleic acid size that you and other groups calculated
will be compared to see how close to the actual value you came.
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Biology of the Cell (Biol 1021)
Conversions and Introduction to Lab Equipment
Metric Units Encountered in Biology and Their American Equivalents
Attribute
Length
Mass
Temperature
Time
Volume
Unit
Symbol
American Equivalent
Meter
m
1m = 3.28 feet
Kilogram
kg
1 kg = 2.2 pound
Kelvin
(Centigrade)
K (C)
Second
s
Cubic meter
(Liter)
Dm3
Tc C = (Tf F-32)/1.8 Tk K = Tc C + 273.15
Same
1L = 1.06 quart; 1cc = 1 cm3 = 1 mL
Prefixes for Metric Units of Measure
Prefix
Symbol
Power
Giga-
G
109
Mega-
M
106
Kilo-
k
103
Centi-
c
10-2
Milli-
m
10-3
Micro-

10-6
Nano-
n
10-9
Pico-
p
10-12
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Lab 1
Biology of the Cell (Biol 1021)
Conversions and Introduction to Lab Equipment
Homework – Due at the beginning of the next lab!!!
Name: _________________________________________________
Complete the following conversions using the above charts. SHOW ALL YOUR WORK!
1. How many liters in one gallon?
2. One inch equals how many centimeters?
Hint: 3 teaspoons equal 1 tablespoon and 4 tablespoons equal ¼ of a cup.
3. How many milliliters in a teaspoon?
4. How many milliliters in a tablespoon?
5. A 10 gigabyte hard drive will hold how many 200 megabyte files?
6. How many microns (another term for micrometers) in a centimeter?
7. How many grams in an ounce? (Hint: 16 ounces in a pound)
8. How many cubic centimeters in 4.67 liters?
9. Convert your weight to kilograms.
10. Convert your height to centimeters.
Additional work to turn in:
1. Completed table of data for all exercises.
2. Completed graph with lines for Exercises 1 and 2.
3. The slope of each line in the above graph.
4. Description of the solid in Exercise 3 and its density.
5. Calculations for Exercise 4.
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Lab 1
Biology of the Cell (Biol 1021)
Conversions and Introduction to Lab Equipment
Lab 1
Exercise 1 – Density of water:
Trial 1
1) Mass of the weighing boat before taring: _______________________
2) Mass of 1 mL of water: _____________________________________
3) Mass after 2nd addition of water: ______________________________
4) Mass after 3rd addition of water: ______________________________
5) Mass after 4th addition of water: ______________________________
6) Mass after final addition of water: _____________________________
Trial 2
1) Mass of the weighing boat before taring: _______________________
2) Mass of 1 mL of water: _____________________________________
3) Mass after 2nd addition of water: ______________________________
4) Mass after 3rd addition of water: ______________________________
5) Mass after 4th addition of water: ______________________________
6) Mass after final addition of water: _____________________________
Trial 3
1) Mass of the weighing boat before taring: _______________________
2) Mass of 1 mL of water: _____________________________________
3) Mass after 2nd addition of water: ______________________________
4) Mass after 3rd addition of water: ______________________________
5) Mass after 4th addition of water: ______________________________
6) Mass after final addition of water: _____________________________
Average of Three Trials
1) Mass of the weighing boat before taring: _______________________
2) Mass of 1 mL of water: _____________________________________
3) Mass after 2nd addition of water: ______________________________
4) Mass after 3rd addition of water: ______________________________
5) Mass after 4th addition of water: ______________________________
6) Mass after final addition of water: _____________________________
Construct a line graph of the results (mass vs. volume) and determine from the slope of the
line the value for the density of the water.
Exercise 2 – Density of second liquid
Liquid ________________________
1)
2)
3)
4)
5)
Weight of the weighing boat before taring: _______________________
Weight of 1 mL of unknown: __________________________________
Weight after 2nd addition of unknown: ___________________________
Weight after 3rd addition of unknown: ___________________________
Weight after 4th addition of unknown: ___________________________
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Biology of the Cell (Biol 1021)
Conversions and Introduction to Lab Equipment
Lab 1
6) Weight after final addition of unknown: __________________________
Construct a line graph of the results (mass vs. volume) and determine from the slope of the
line the value for the density of the liquid that you selected for this experiment.
Exercise 3 – Density of a Solid:
Description of solid: ______________________________________________
1) Volume of water before adding the object: _______________________
2) Mass of the object: _________________________________________
3) Volume of water after adding the object: _________________________
4) Calculate the density of the solid _______________________________
Exercise 4 - Determination of the size of a molecule:
Monolayer Thickness Data and Calculations
Number of drops of oleic acid solution to equal 1.0 ml = ___________
Number of drops of Oleic Acid Solution Used = ___________
Volume of oleic acid used to create the oil slick or clear area = ____________________.
Diameter of clear area:
Trial 1 = ______________ Trial 2 = ______________ Trial 3 = ______________
Average diameter from three trials = ______________
Based on the average diameter of the oil slick, determine the average radius of the “circular oil slick” and
then calculate the area of the clear surface. Calculate the average area of the oil slick: A = r2. This is
the area covered by the oleic acid.
Area of the oil slick = ___________________
Use the following equation to calculate the thickness of the layer of oleic acid on the water:
V = ()(r 2)(h)
In this equation V is the volume of pure oleic acid, r = the radius of the clear acid region on the
water (diameter/2), and h is the thickness you want to find. If we assume that the layer is a single
molecule thick, the answer to this calculation is the size (the length) of a single molecule of oleic
acid. (Show calculations)
Based on your work, how big is an oleic acid molecule in nanometers? You will need to convert
from centimeters to nanometers.
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