Metrology (1310)
Purpose: This exercise is to introduce students to the metric system and common laboratory
equipment they will be working with during the course. You are to record the steps performed
and your results in your laboratory notebook following cGMP documentation guidelines.
Materials
Meter sticks, thermometers, balance, 25ml, 100ml graduated cylinders, 250ml beakers, pennies,
test tubes, deionized water, spatulas, 5ml, 10ml, pipette, aids, hydrogen peroxide, potato,
balance, mortar and pestle.
The Metric System (you don’t have to record this section)
Just as scientists use unique names to identify a single species that is recognized globally,
scientists use the metric system as a universal measurement system. The world for that matter,
the sole exception being the United States, uses the metric system as it logical and units are
easily converted. Thus, since this is a science class we will be using the metric system exclusively
to make our measurements.
The metric system has four base units:
Base Unit
Measurement
Meter (m)
Gram (g)
Liter (L)
Celsius (°C)
length
mass
volume
temperature
We can simply add prefixes to the base unit to change the value of the measurement by factors
of ten.
Prefix
Multiply
Divide
kilo (k)
1000
hecto
(h)
100
deka
(da)
10
Base
deci (d)
centi (c)
milli (m)
micro (µ)
1
1
0.1
0.01
0.001
0.000001
The Greek prefixes to the left of the base are larger so numbers get smaller as you move the
decimal to the left.
The Latin prefixes to the right are smaller so the numbers get larger as you move the decimal to
the right.
Hint: an easy way to remember the prefixes is this mnemonic
King
kilo (k)
Hector
hecto (h)
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Died
deka (da)
By
Base
Drinking
deci (d)
Curdled
centi (c)
Milk
milli (m)
Monday
micro (µ)
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Example: we have a large number with millimeters as the unit = 7550mm.
A good unit to convert to would be the base unit of the meter. 7550 x 0.001 = 7.550m
You can also perform this conversion using our memory device and counting the number of
steps from your current unit to the desired unit. Move the decimal point the same number of
steps in the same direction you did when counting prefixes.
There are three steps to the left from milli to the base. We move the decimal point three to the
left.
7550.  becomes 7.550
We move the decimal six steps to the right when converting 0.00123Kg to mg.
0.001230  becomes 1230.
Hint: Be careful of the micro (µ) prefix that we will use in class.
It is three steps to the right of the milli (m) prefix or is 1000 times smaller!
Practice Problems
100mm to cm
___________
5000Kg to g
___________
0.00100µL to ml
___________
10daL to dl
___________
701.30hm to cm
___________
*50cc to ml
___________
3
*250mL to cm
___________ *Hint: Think of these measurements in three
dimensions
Accuracy and Precision
When making measurements in the laboratory is it important to consider the difference
between accuracy and precision.
Accuracy is the proximity of the measurement to the true value.
Precision is the repeatability of the measurements.
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The first target exhibits accuracy but you would question the experimenter’s techniques as they
are inconsistent.
The second target is inaccurate but precise. The experimenter is performing the procedure
consistently and may not be at fault. It may be the procedure itself.
You should strive for both accuracy and precision in the laboratory, and be able to interpret
your data if one or both are lacking.
Taking Measurements
When measuring a piece of equipment you are expected to report the value to one more
significant figure (decimal place) than the graduations allow.
What is the correct measurement? __________cm
Why?
When reading liquid volumes in a graduated cylinder or pipette you need to read the bottom
curvature of the water or the meniscus. Read the two volumes below to the greatest
accuracy.
Grad cylinder____________mL
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Pipette_____________ml
Note- pipettes are calibrated as TD or (to
deliver)!
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Test your knowledge - Draw a line matching the picture with the name
Pipette aid
Flask
plastic pipette
beaker
microscope slide
micropipette
test tube mortar/pestle
hot plate stirrer
Petri dish
scalpel
test tube holder
Procedure (begin recording data in your notebook here include procedure section and data
section. Good idea to break into sections A, B, C etc.)
Part A - Degree of Accuracy
1)
Observe the smallest place value represented by the lines on your meter stick (on the
metric side). Record this value, with the appropriate unit as the "smallest certain
place value" in the form of data table A in your notebook.
2)
Add one decimal place value (i.e. tenth becomes hundredth, or hundredth becomes
thousandth) to the value from the previous step. This is your estimation digit for this
instrument. Record this value, with the appropriate units, "in data table A in your
notebook.
3)
Repeat steps 1 and 2 for each of the following instruments; thermometer, balance,
25ml graduated cylinder, 100ml graduated cylinder. Record these values, with the
appropriate units, in the form of a data table your notebook.
Suggested Table A for notebook
Instrument
Meter stick
Thermometer
Balance
25ml grad cylinder
100ml grad cylinder
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Smallest place value
Estimated value
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Part B - Measuring Mass
1)
2)
3)
4)
5)
6)
Tare your calibrated balance.
Determine the mass of a clean, dry 25ml graduated cylinder. Record this in the form
of a data table B in your notebook.
Add 10.0 ml of DI water to the graduated cylinder. Dry the outside of the cylinder to
avoid massing extra water.
Mass the graduated cylinder with the water inside. Record this value in data table B
in your notebook.
Is there another way to do this with fewer steps? Explain.
a) Using an electronic balance, find out how many pennies it takes to make 10 grams
and round to the closest penny if necessary.
b) How many grams does 10 pennies weigh rounded to 2 significant digits?
Part C - Measuring Volume
7)
8)
9)
10)
11)
12)
Measure out a random sample of water in the 25ml graduated cylinder. Record the
volume and units, to the highest degree of accuracy in Table C in your notebook.
Have your lab partners verify the accuracy of the volume of water.
Repeat steps 9 and 10 with the 100ml graduated cylinder.
Carefully place a penny in the 100ml graduated cylinder. It must be completely
submerged, and the volume must be no greater than 100ml. Record the new water
level and determine the volume of the penny.
Using a 10ml and 5ml graduated pipettes and manual pipette aid, fill a tared test
tube in a beaker with 25.0ml DI water, and determine the mass of the water only.
Density of water is 1.00 g/ml. What is the mass of your water? Was your pipetting
accurate?
Part D –Potato Catalase
Hydrogen peroxide H2O2 is a byproduct of cellular metabolism and can be damaging to cells if it
is not converted into water and oxygen in the presence of catalase.
2H2O2 + catalase---------> 2H2O + O2
Catalase is an enzyme. Enzymes are biological catalysts that lower the activation energy of
reactions and allow them to proceed faster or to even take place at all. We are going to use
naturally occurring catalase from red potatoes to breakdown our H2O2. This will result in the
formation of foam from the O2 that is released. We can estimate catalase activity indirectly by
the height of the foam.
This is an introductory experiment to measure enzyme activity and you will need to practice
your metrology skills learned earlier in this lab. Attempt to be both accurate and precise when
measuring your reagents as small errors can lead to poor data!
Procedure
1. You will find red potatoes on the center bench in the lab. Take about half of a small
potato and dice it into small pieces (be careful).
2. Grind the diced cubes with a mortar and pestle until there and no large pieces.
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3. Using the electronic balance, weigh the potato and place into the test tubes according
to table 1.
4. This is a good place to formulate your hypothesis using the values in the table below.
What’s going to happen and why? Will all the tubes be the same?
Hypothesis?
5. Pour about 30ml of H2O2 into a 50ml beaker.
6. Use a motorized pipettor and pipette and add 5mL of H2O2 from the beaker to test tube
1.
7. Quickly but accurately repeat for the remaining 4 tubes.
Table I
Tube number
Potato
amount
Amount H2O2
1
0.0g
2
0.2g
3
0.5g
4
1g
5
2g
5mL
5mL
5mL
5mL
5mL
8. You should see foam being generated in most of the tubes.
9. Wait ten minutes and then using a metric ruler measure the height of the foam of each
tube in cm and record in table 2.
Table 2
Tube number
Potato
amount
Foam Height
cm
1
0.0g
2
0.2g
3
0.5g
4
1g
5
2g
What we just tested is the effect of varying the amount of enzyme available to breakdown the
substrate or H2O2 which did not change.
Did varying the amount of potato (enzyme) make a difference?
Generate an XY scatter plot of the results in Excel.
Graphing in Excel
The first thing to consider when graphing is deciding what the dependent and independent
variables are. The independent variable (x-axis) is the one that is predetermined by the
parameters of the experiment. The dependent variable (y-axis) is the one we are testing for and
don’t know yet.
In the potato enzyme experiment, the amount of potato was the independent variable and the
foam height (enzyme activity) was the dependent.
1. Open an Excel spreadsheet.
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2. In cell A1 type the first value of the independent variable (x-axis)
3. Place all the remaining x-values in order directly underneath A2, A3, A4, A5, etc.
4. In cell B1 type the first value of the dependent variable.
5. Place all the remaining y-values in order directly underneath B2, B3, B4, B5, etc.
6. Highlight only the cells with information in them.
7. Locate the chart wizard icon or use the insert button.
8. Select scatter and a chart type with connected data points (second row to right).
9. You should see your chart. Look at the trend. Does it make sense?
10. Go to the layout tab and add a descriptive but concise chart title and axes labels.
11. You may wish to plot more than one y against a particular x.
12. Simply add the second y values in column C, third in column D etc.
Finally conclude your notebook entry with any notable results or possible errors that need
documenting. Also, it is here you can also suggest issues with the protocol and some
possible future solutions. Be fairly brief.
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