CHM 1025C
Experiment 3
LABORATORY
MEASUREMENT  THE METRIC SYSTEM
GOALS:
(1) To
learn to manipulate laboratory instruments to measure length, mass, volume,
count, and time.
(2) To
introduce the relationship of the metric units to English units.
(3) To
learn the difference between precision and accuracy.
(4) To
learn to calculate a deviation and a per cent error in experimentation.
INTRODUCTION
In our everyday world we are faced with
many measurements. For each measurement there
must be a UNIT of measure. Some are
simple, some are very complicated. After
12 years of schooling most students know how a mile gallon, pound, foot, inch,
yard quart and ounce relate to everyday life.
There are all measures of the ENGLISH system of measurement, which
system is not used in
Have you heard of a CALORIE? KILOWATTHOUR? On your JEA bill electricity is measured in
kilowatthours, water in cubic feet. What does 55 miles/hour really mean. Pollution is
measured in Parts per Million (ppm) or Parts per
Billion (ppb). These are multiple
dimension measures.
THERE ARE 5 CLASSIFICATIONS OF SINGLE
(SIMPLE) DIMENSION UNITS. They are: LENGTH MASS COUNT TIME VOLUME
(length cubed)
All other measures are combinations of
these simple dimensions.
Speed or Velocity is length per
time;
(Two Dimensions)
Acceleration is change in
velocity per unit of time:
(Three Dimensions)
Force is mass times acceleration:
(FOUR DIMENSIONS)
Work is force
times distance moved:
(FIVE DIMENSIONS)
Power is work per
time:
(SIX DIMENSIONS)
In freshman chemistry, students seldom advance
beyond one or two dimension measures.
Some of the two dimension measures to be calculated in later lab
experiments are: Density, % Recovered, Molecular Mass, Mole Ratio, Gram Molar
Volume Constant, %
Purity, Molarity, Molality,
% by Mass, and Normality (no longer
used).
PROCEDURES
PART 1: LENGTH
You will work with a lab partner only
on this part of the lab.
1. Obtain a two meter stick from the equipment
cart of two one meter sticks. Tape a
sheet of paper to the wall. Mark your
height on the piece of paper.
2. Measure your height in inches and in
centimeters (each person) using either two meter sticks or the special two
meter stick. Record the data using at
least 3 significant digits.
3. Calculate the number of centimeters in
one inch by dividing your height in centimeters by your height in inches.
Example:
or 1.00 in. = 2.59 cm.
4. The True Value is 1.0000 in. = 2.5400
cm (exact). Find the difference between
the true value and your experimental value.
This is called the deviation.
Example: Experimental value 2.59 cm/in
True value 2.54
cm/in

Deviation
.05 cm/in
5.
Calculate your percent error using the formula:
% Error =
Example: % Error =
= 2 %
6. Now measure your height in centimeters
and inches using only a one meter stick.
(You will have to move the stick to make the measure; this may introduce
error.)
7. Again calculate the number of
centimeters in one inch, the deviation from the true value, and the % error.
PART 2: FINDING VOLUME FROM LENGTH
8. Obtain an object of unknown volume from
the lab cart (Block of wood, metal bar, or your textbook. (Record the number of this object, if labeled
or description).
9. Measure the length, width, and height
of the object to the nearest
0.1cm and to the nearest 0.125 inch (one eighth) or 0.0625 inch
(one sixteenth) using a ruler.
10. Record the data and calculate the volume
using the formula (both cm^{3} and in^{3}):
Volume
= length x width x height. V = _______ cm^{3} = ________ in^{3}
The correct value is 16.48 cm^{3} = 1.000 in^{3}
PART
3: MASS
In the laboratory we use several
devices to measure mass. They are called
balances. For large masses we use triple
beam balances. Below are two sets of
directions for the two main types of triple beam balances.
Thought question: Why are
they called triple beams?
TRIPLE
BEAM BALANCE INSTRUCTIONS:
A. With
the pan empty, adjust all weights to zero.
Be certain all weights are in the zero groove.
B. Use
the damper button to bring the pointer to a steady position. Depress the damper. If the POINTER is not on the center line,
adjust the ADJUSTMENT Screw until the pointer is centered on the middle line.
C. Load
the balance.
D. Move
the 100 gram weights until the pointer drops below the center line. You have set 100 too many grams. Move the 100 gram weight back one
position. If the object exceeds 500,
hang the weights in the hole outside the end of the POINTER, reset to zero and
start again.
E. Repeat
step D with the 10 gram weights.
F. Slide
the gram weight until the POINTER is centered.
G. Read
the weight to the nearest 1/10 gram.
3. Use an object such as your car keys to
calculate the number of grams in one ounce by first using a triple beam balance
and some balance that will record masses in ounces. If there is no device, skip
this part of the experiment.
Mass of Object = __________g (triple beam)
Mass of Object = __________oz (some ounce measuring
device, if available)
4. The true value is 1 oz. = 28.35 g. Calculate the deviation and percent error.
5. Obtain an unknown mass of less than 100
grams from the lab cart. Record its
number.
6. Find the mass of the unknown using the triple beam
balance. Record your data to the nearest 0.1 g.
7, Repeat steps 5 and 6 using a mass of
greater than 1000 grams.
Have the lab instructor check your
results.
Top
Loading Balances (0.01 g on each island):
For smaller masses, we use top loading
balances and analytical balances.
Over the years the United States Ming
has changed the ratio of different metals used in making the various
coins. The last change for the penny
occurred in 1982.
Following is a brief chronology of
the metal composition of the onecent coin (penny):
Current Penny: 
Specifications Composition: CopperPlated Zinc: 2.5%
Cu, Balance: Zn 97.5 % Mass: 2.500 g Diameter: 0.750 in., 19.05 mm Thickness: 1.55 mm Edge:
Plain 
1. Obtain
three pre1982 pennies and three post 1982 pennies. Weigh each penny on the 0.01g top loaders at
each island in the lab.
__________g (6
pennies) Average Mass of One:
_________g
__________g
(13 pennies) Average Mass of One:
_________g
__________g
(25 pennies) Average Mass of One:
_________g
Finding
the True Value:
Balance
Wheat Penny Zinc Penny
Triple Beam
____________g
____________g
Top Loader (0.01g)
____________g
____________g
Top Loader (0.001g)
____________g
____________g
(only one in the lab at
the front desk)
Analytical Balance ____________g ____________g
(only one in the lab at
the front desk)
Precision
versus Accuracy:
Dart
Board A
Dart Board B
Dart Board C
In the World of Chemistry Video: “Measurement” toward the end of the film
there was a discussion of Accuracy and Precision in experimentation.
Precision: The
agreement of repeated measurements of a quantity with another.
Accuracy: The agreement between the measured quantity and
the accepted
(or true) value
In your post lab report, write a discussion of
accurate and precise. How did the masses of the same type of penny vary?
Uncertainty: The
degree on inexactness in a measurement obtained from
an instrument.
In your post lab report, write a discussion of
exactness and uncertainty in laboratory measurements.
An element found in nature has a mass number,
which is a whole number, and an atomic mass, which is a rational number. On the
periodic chart, the masses of elements are reported as atomic masses, not mass
numbers. Why?
PART
4: VOLUME
PROCEDURE FOR READING A GRADUATED
CYLINDER

A.
Note the two successive numbers on the graduations the diagram shown to the left: note the 50 and
45 numbers on the 50 mL graduate. B. Count the spaces between the lines
of 50 and 45.
In the diagram there are 5 spaces between 45 and 50. C.
Therefore C. The difference between 50 and 45 is 5 mL
There are five spaces. Divide the number of milliliters by
the number of spaces: 5 ÷ 5 = 1
milliliter for each line. (± 0.1 mL) 
D. When reading volumes, count the
number of lines between the bottom of meniscus and the next lower number. In the diagram there are three lines between
the meniscus and 40 ml line. Therefore
the reading is between
43 and 44 milliliters.
E. Estimate the distance between the
lines to estimate the 0.1 mL.
This reading is 43.8 ± 0.1 mL.
F.
In the diagram to the right, proper eye Alignment
is a direct line of sight toward the meniscus. This
will avoid parallax error, This reading Is
87.5 ± 0.1 mL It is two line
below 90 and seven lines above 80. G. You instructor will demonstrate
the dark line technique (The dark line must be several lines
below the meniscus) 

2. Obtain one of the bottles (milk, soda
pop or liquor) and fill each with water.
Record the volume in ounces or quarts.
3. Using the appropriate size graduated cylinder,
measure the volume of water contained in the bottle and record that volume.
4. Calculate the number of milliliters in
one ounce. (63 oz. = ˝ gallon, 32 oz. =
1 qt)
5. The accepted value is 29.5 ml = 1
oz. Calculate your deviations and
percent error.
6. Record the volumes of liquid in each of
at least 6 different graduated cylinders on the instructors table or the side
counter.
7. Record the cylinder numbers/capacity. Record the volumes using as many significant
digits as each graduated cylinder allows.
Have the lab instructor check your
results.
PART 5:
COUNT
There are many counting units commonly
used. Dollars and cents are counting
units. Dozens, cases, six pack, each, pack, ream of paper, and gross are terms
commonly used. (What is a “Baker’s” dozen?)
In chemistry we use the mole: 6.023 x
10^{23} objects = 1 mole. A mole
is sometimes thought of as a “chemist’s dozen”.
In CHM 1025C or CHM 1032C (especially hospitals) you may encounter
another counting unit, the EQUIVALENT. It is the first cousin to a mole, so to
speak.
However, 20 years ago it was removed from the first year chemistry
textbook.
Bean Jar or Gum Ball Experiment may be performed if time permits during this Measurement lab, otherwise during our first crucible experiment when we study mass relationships of chemical reactions we will attempt this experiment.