GENERAL CHEMISTRY LAB REPORTS
I
Objective (~5%)
State the objective of experiment – what is the scientific goal, not just statement of
the measurements that are to be made
II
Introduction (~5%)
Provide short discussion putting the subject matter in context – why we should care
III Experimental Procedure (~5%)
Can refer to manual, but describe any changes made to outlined procedure.
IV Experimental Results (~30%)
Data table
Graphs as appropriate
- Axes labeled
- Scales fully utilized (data fill the graph)
- Title on graph
Appropriate significant figures and units
Qualitative observations
Sample calculations included for all equations (can be handwritten)
Only need to show one sample for each calculation (i.e. just 1 trial, not all trials)
V Discussion (~30%)
All questions answered correctly (both in-lab and post-lab questions)
Include questions as well as answers
Top marks only if expand on answer and provide answer as
complete paragraph and thought
Data compared to expected results or literature values
% error given if know literature value
Standard deviation if have multiple repeats for a value
Possible sources of errors (not just human error) - Possible improvements
Provide reference citations for any literature values or other cited information
VI Conclusion (~10%)
Overall conclusions *** This last item is critical, don’t just stop with results.
Comment on what the results mean relative to initial theory
VII Reference Citations (~5%)
VIII Overall Impact of Report (~10%)
Neatly typed or printed
Correct spelling
Should be evident that time and thought spent on report
SAMPLE LAB REPORT
Student:
Josephine Chemistry
Lab Partner: Mad Max
[Date
experiment
run in lab
Sept 15, 2015
FREEZING POINT OF SOLUTIONS
OBJECTIVE: The objective of this lab was to demonstrate the impact that solutes can have
on the freezing point of solvents in solution. We did this by preparing a range of solutions of
NaCl and water and then measuring the temperature at which those solutions froze.
[What is the
scientific
objective?]
INTRODUCTION: It is well known on the streets of Philadelphia, or at least in the suburbs,
that salt can be put on roads in the winter in order to melt snow and ice. According to our
textbook,1 adding salt to water should lower the freezing point according to a linear
relationship.
Tf, sol’n = Tf, pure – (Constant * msol’n)
(Eqn. 1)
This equation says that the difference in freezing point temperatures for a mixed solution and
for pure H2O is dependant on the concentration of the solution when measured as molality, m.
[Discuss the
chemistry
that is being
explored in
the lab.]
m sol'n =
moles NaCl
kg H 2 O
[Include
reference
citations]
(Eqn. 2)
PROCEDURE: We followed the procedures outlined in the course manual, CHM 111
General Chemistry Laboratory Manual, LaSalle University, Fall 2015. However, we
modified the procedure by using a LoggerPro computer probe to measure the temperature
rather than using the normal thermometer that was specified in the procedure.
[Can refer to
class manual.
But highlight
any changes.]
EXPERIMENTAL RESULTS
We prepared four different solutions of NaCl in water and measured their freezing points.
Trial #
1
2
3
4
NaCl
(g)
0.00
1.23
2.36
4.00
H2O
(g)
100.00
100.00
100.00
100.00
Freezing Pt
(°C)
0.10
-0.51
-0.63
-1.35
[Table of
raw data.]
[For Trial #4,
keep all sig. fig’s,
even if have
trailing 0’s at end.]
These data were converted into concentrations in units of molality using equation #2.
Trial #
1
2
3
4
Molality (m)
(mol/kg)
0.000
0.210
0.404
0.684
Freezing Pt
(°C)
-0.10
-0.51
-0.63
-1.35
Sample molality calculation for Trial #2:
m=
1.23g NaCl  1mol NaCl  1000gm H 2 O 
×
×
 = 0.210 mol / kg
100.00g H 2 O  58.45g NaCl   1kg H 2 0 
[Table of
calculated
results.]
[Show sample
calculations,
but only for 1 trial.
Can be handwritten]
o
Freezing Temp. ( C)
[For graphs…
- fill entire plot area
- label axes
- include units
- use data markers
for data points.
“data protectors”]
Freezing Pt vs. Molality NaCl
0.0
-0.4
-0.8
-1.2
-1.6
0.0
0.2
0.4
0.6
Molality of NaCl (mol/kg)
0.8
[Graphs can be
attached at end of
report]
QUESTIONS
1.) Graph the data of freezing point vs. molality. What type of relationship
between the two variables do you see?
The data on the graph demonstrate that there is a linear relationship between
concentration (molality) and freezing point. As the concentration of NaCl in the
solution was increased, the freezing point decreased at a constant rate.
[Include all in-lab
and post-lab
questions in the
report]
2.) Using the data on your graph, what concentration of NaCl is needed to drop
the freezing point of water to -1.0°C?
By drawing a line through the data, one can see the expected relationship
between concentration and freezing point. In the graph above, we see that we
can interpolate to determine that a molality of approximately 0.52m will give a
freezing temperature of -1.0°C.
[Answer in paragraph
form. Not just one
word answers.]
DISCUSSION
While the experiment was successful, our data may have been affected by several
sources of error. The temperature probe may not have been accurate. This would
have shifted our results up or down on the graph. Similarly, we assumed that the
probe was measuring the average temperature of the solution. But it is possible that
the probe was located at a slightly warmer or colder place in the beaker, and therefore
did not reflect the temperature of the overall solution.
[Compare results
to literature
values.
Discuss possible
sources of error]
CONCLUSION
We were successful in demonstrating that there is a linear dependence between the
concentration of a solution and the freezing point of that solution. Adding NaCl to the
solution slowly decreased the freezing point, making it easier for the ice crystals to melt.
This is why putting salt on icy roads in the winter causes the ice to melt even though the
outside temperature is below the normal freezing point of pure water.
REFERENCES
1. John W. Hill and Stuart Baum, Chemistry and Life, Prentice-Hall, Inc, 2000.
2. CHM 111 General Chemistry Laboratory Manual, LaSalle University, 2015.
[Was experiment
successful?
What did you
learn?]
[Give reference
citations for any
material taken
from elsewhere.
This includes
literature values]