GenChem
2nd
Class
Introduction to Measurement
Make sure you are sitting
with your group members!
Today’s Agenda:
 Safety Agreement Check
 Review of notebook
 Math review
 Review of the experiment
 Perform lab work
 Analyze results (including calculations)
 Discuss writing the report
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Safety Agreement
Have you done it?
We can not let you
work in our labs if you
don’t agree to be
safe.
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Notebooks
 Exchange your notebook with one of your
group members.
 Evaluate the notebook. Is it suitable? Is
it being correctly used? Share your views
with the owner.
 Return the notebook to its owner.
 As a group, make a list of the things you
expect to be putting in your notebook today.
GenChem
Notebooks
 As a group, make a list of the
things you expect to be putting
in your notebook today.
 Title, date, time, names of partners.
 observations, measurements,
descriptions of what was done.
 signature at the end of the session.
 instructor initials
GenChem
Lets Practice
The Amazing Oscillating
Chemical Reaction
• Observe the reaction
• Characterize the reaction
• Determine a variable that
can be measured and
measure it.
• Plot the results and draw a
conclusion.
And record it all in your notebook!
GenChem
Let′s think!
Density is an intensive property
that is commonly used to
differentiate and separate
plastics during recycling.
What do you need to
measure to determine the
density of each of the
plastic pieces?
Density = mass/volume
(r = m/V)
mass and volume must be measured to
determine density
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Pre-lab assignments
revisited
GenChem
Let′s think!
Revisiting
Mass Measurement
DON’T FORGET
In
groups
revisit
 your
Balances
must
not be
what youmoved
will need to
do
to make
reliable
 Only
glass
or metal
mass measurements.
objects
can be put on the
pan
 They must be left clean.

Let′s think!
GenChem
Volume Measurement
In your groups review your
responses to the following pre-lab
question and come up with a
consensus answer.
Describe how to use a graduated
cylinder to reliably and accurately
measure the volume of a liquid
Let′s think!
GenChem
Volume Measurement: making
linear measurements.
In your groups your responses to the following pre-lab
question and come up with a consensus answer.
Lengths are measured using rulers. Describe why a vernier
caliper is preferred over a common ruler for this
experiment.
Make sure you
know how to use it!
GenChem
Let′s think!
Volume Measurement: linear
measurements vs displacement.
In your groups review your responses to the
following pre-lab question and come up with
a consensus answer.
Which technique do you think will provide
the more accurate measurement of the
coin’s volume - displacement or linear
measurement? Justify your choice.
How could you prove one
to be more accurate?
Let′s think!
GenChem
Volume Measurement: linear
measurements.
In your groups review your responses to the
following pre-lab question and come up with a
consensus answer.
Make an outline of the operations you will have to
perform to determine the volume of a coin by making
linear measurements. Include all the equipment and
materials you will need to use.
Will this work for the plastic pieces?
Modify your procedure as needed.
Let′s think!
GenChem
Volume Measurement: displacement.
In your groups discuss your responses to the
following pre-lab question and come up with a
consensus answer.
Make an outline of the operations you will have to
perform to determine the volume of a coin using
displacement. Include all the equipment and
materials you will need to use.
Will this work for the plastic
pieces? Modify your
procedure as needed.
What if it
floats?
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Identifying
Unknown
Samples
Once you have determined the density
of an unknown piece of plastic, what
else will you need to know to identify it?
Density values for candidate plastics
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Determining Known Values
You will need to know the densities of the six
Your group will be responsible for
possible plastics to identify your unknown. The
determining
the are
density
offor
one
plastic
following samples
provided
your
use.
Polyvinyl chloride ( PVC)
Polyethylene
terephthalate( PETE)
High Density Polyethylene
( HDPE)
Polypropylene ( PP)
Low Density Polyethylene
(LDPE)
Polystyrene ( PS)
GenChem
Let′s explore!
First Challenge
Determine the density of your assigned plastic.
Measure the volume both ways and compute the
density separately for each.
Available resources:
 4 pieces of PVC.
Rulers, vernier
calipers.
Balances (TC 4).
 Glassware.
Design a feasible
procedure and
implement it!
You have
30 minutes
Let′s think!
GenChem
Within your group, review your results and
decide on a value for the density of your
plastic. Prepare a report to the class.
Choose a reporter. That person is to report to the
class the one value to use for that plastic, your
justification for selecting that value and your
confidence in that value.
Let′s think!
GenChem
While preparing your report consider the following
 Did everyone have the same value? If not,
how did you decide on one number to report?
 Did both volume determination methods
produce the same value? If not, which one did
you chose to use and why?
 What is your confidence in your answer?
Does your reported value reflect your
confidence? How so?
GenChem
Let′s think!
Known values for plastic densities.
Reports to the class
Each group is to report.
Plastic
HDPE
 The known value to use for
that plastic.
LDPE
 The justification for selecting
that value.
PP
 The confidence in that value.
PVC
PET
PS
Density (g/mL)
GenChem
Let′s explore!
Final Challenge
Identify your unknown plastic pieces.
Available resources:
 Densities of known plastics
 Pieces of unknown plastics.
 Balances;
Design a
feasible
procedure and
implement it!
 Rulers, vernier calipers;
 Glassware;
You have
20 minutes
The Report
GenChem
To be submitted BEFORE leaving class:
You will now write your
report for this
experiment. It is a
limited report. Only the
indicated sections are
required.
 Raw data. A copy of all
measurements and observations you
collected in lab.
 Calculations. Examples of the various
calculations performed.
To be submitted next week:
 Results. An organized presentation of
the results obtained.
 Discussion. A discussion of the
results obtained. For this report (only)
this is to be the answers to the Wrap-up
Discussion questions.
Calculations
GenChem
• From p. 65 of your Technique Book:
Calculations. Examples of all calculations
performed to manipulate the numerical data.
Include one example for each type.
• From p. 70 of your Technique Book:
One example for each type of calculation.
Each example should consist of three parts:
– The formula that describes the calculation
– The formula in use
– The answer
Let′s think!
GenChem
Calculations:
Outline
In your groups:
What were the major goals of today’s lab?
1.Find densities of known plastics
2.Identify unknown plastic
Let′s think!
GenChem
Calculations: Outline
In your groups:
Identify the important calculations that should
be included in your calculations section
1.Known Plastics
•
•
Volume of plastic
Density (can be taken from the graph rather than
actually calculating)
2.Unknown Plastics
•
•
Volume of plastic
Density of plastic
Let’s apply
Calcuations
GenChem
Calculations should always use a three step
format:
Write out the equation
Plug in your numbers
Give the answer
This method ensures that your instructor can
follow your thought process during the
calculation.
Do not forget to add units and watch significant
figures during your calculations!
GenChem
Let’s apply
Calculations: Goal 1
The first calculation we listed is volume:
Volume of a rectangular prism:
length x width x height = volume
1.05 cm x 1.26 cm x 1.82 cm =volume
volume=2.41 cm3
GenChem
Let’s apply
Calculations: Goal 1
The second calculation we have listed is
density. We obtained this value from the
graph, but it would be helpful to make a note
in the calculations so that the reader does
not think you forgot one:
Density of known plastic: Determined from
the slope of the graph
GenChem
Let’s apply
Calculations: Goal 2
The first calculation of goal 2 is the same as
that of goal 1: volume. Since we have
already shown this calculation, we do not
need to show it again.
If we calculated the volume a different way,
then we would need to show a second
calculation.
GenChem
Let’s apply
Calculations: Goal 2
The last calculation we have is density of the unknown
plastic. Since we only had one piece of plastic, we do not
have a graph to use to calculate density, so we have to use
a formula.
Density:
GenChem
Calculations:
Things to Remember
Include a calculation for all types of
calculations that you do, but only
include one example for the type of
calculation
Watch significant figures and units
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Results
From p. 65 of your Technique Book:
Results. An organized presentation of the
observations and calculated results. This section is
frequently dominated by figures, tables and graphs.
It will contain little to no text.
From pp. 67-8 of your Technique Book:
Results. An objective and clear description of
experimental findings following an appropriate
order and including relevant:
Tables
Graphs
Figures
Let′s think!
GenChem
Results:Outline
In your groups:
What were the major goals of today’s lab?
1. Find densities of known plastics
2. Identify unknown plastic
GenChem
Let′s think!
Results: Outline
In your groups:
Identify the important results that should be included in
your results section
1.Known Plastics
•
Dimensions of plastic
–
–
•
•
Linear measurement method
Displacement method
Mass of plastic
Density of known plastic
2.Unknown Plastics
•
•
•
•
Dimensions of plastic
Mass of plastic
Density of unknown plastic
Proposed identity of unknown plastic
GenChem
Let’s apply
Results: Goal 1
In a labeled table, compile all of the items on
your list in a table that follows a logical
order.
Table 1. Density determination of known plastic PETE.
Test
Average
Mass (grams)
Volume (mL)
3.320
2.41
1
54.000
40.00
2
16.000
12.00
3
24.440
18.14
GenChem
Results: Goal 1
Let’s apply
It also might be helpful to display this information in a graph
as well. If we plot the volume on the x-axis and the mass
on the y-axis, the slope will be the density of the plastic.
Graph 1. Known PETE mass vs. volume measurements.
60.000
Mass (grams)
y = 1.35x
R²
= 1.00
50.000
40.000
30.000
20.000
10.000
0.000
0.00
10.00
20.00
30.00
Volume (mL)
40.00
50.00
GenChem
Let’s apply
Results: Goal 1
Sometimes, more than one table should be
used to portray all of the results from a
single goal.
Goal 1 can be split in to two parts:
A detailed table for your plastic and graph
A summary table for all unknowns
GenChem
Let’s apply
Results: Goal 1
Table 1. Densities of known plastics
Known plastic
Average density
Literature
sample identity
(g/mL or g/cm3)
density (g/cm3
PETE
PS
HDPE
LDPE
PP
PVC
1.38
0.729
0.89
0.826
0.853
1.03
or
g/mL)
0.90-0.91
1.3-1.4
0.95-0.97
0.92-0.94
1.3-1.6
1.0-1.1
GenChem
Let’s apply
Results: Goal 2
Sometimes, it makes more sense to list
numbers and answers in a clear order rather
than putting them in a table.
Density of unknown plastic: 1.38 g/cm3
Identity of unknown plastic: PET
(Polyethylene terephthalate)
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Results:
Things to Remember
Only include results that are important to
the conclusions that you make
Be careful about the amount of significant
figures you have, especially when copying
tables that you’ve made from Excel
GenChem
Let’s apply
Wrap-up Discussion
Explain why significant figures are important to
measurement and what they signify.
Of the measurements you made, which were
more precise; the mass measurements or the
volume measurements?
Is it practical to use density to separate
plastics? Explain.
Propose another way to separate plastics
making use of a different property than density.
Looking ahead to next week
GenChem
We’ll be investigating the phenomenon known as
“absorption spectroscopy”, the most common
method used to count molecules in solution.
A   bC
Don’t forget that you’ll
need your own food
sample to evaluate!
Directions are in the
experiment guide