Group Experimental Design Lab Report

SAMPLE Pre-lab1. The main goal/purpose of the experiment is (what are you trying to discover in this lab):
2. The hypothesis(es) we seek to test in this experiment is(are) (what is the basis of your
experiment, see your text):
3. The key question the experiment seeks to answer is (what problems are you
addressing?):
4. The controls involved in this experiment are (a control is used to minimize the unintended
influence of other variables on the same system):
5. The key concept(s) or theory(ies) behind the experiment is(are) (define terms, can you
explain the relevant theory):
6. The important technique(s) used in this experiment is(are):
Please describe:
7. The experiment is based on the following assumptions (identify your assumptions and
determine if they are justifiable):
8. The data that will be collected in the experiment are (what do you plan to record in your
notebook)
9. The potential consequences of the experiment are:
10. The point of view behind the experiment is (make sure it’s scientific).
11. What special safety precautions do you need to be aware of for this experiment?
EXPERIMENT #2 – DENSITY – Using Experimental Techniques to
solve an inquiry-based problem
Project:
A group of archeologists discovered the remains of an ancient city dating back to one thousand years ago. They found some objects that
they suspected were made of a material that was invented in the 1800s. This would, of course, be quite controversial. Before they could
take the samples back to a more sophisticated lab for further investigations, they decided to do some simple tests on the remote site to
gather as much information as possible. As a member of the team, you are assigned the task of figuring out the density of the sample as the
density of the suspected material is well documented so you can compare them. Specifically, you are asked to:
1. Design two experiments to determine the density of the object, using the limited resources available to you, including a
balance, some volumetric equipment such as graduated cylinder, Erlenmeyer flask beakers, rulers, etc. Hint: What are some
ways scientists can determine the volume of an object?
2. Perform error analyses and compare the two methods and report the method and density that you believe is more reliable.
Individual Pre-lab
1. The main goal/purpose of the experiment is (what are you trying to discover in this lab):
2. The hypothesis(es) we seek to test in this experiment is (are) (what is the basis of your experiment, see chapters on physical
properties and density in your text):
3. The key question the experiment seeks to answer is (what problems are you addressing?):
4. The controls involved in this experiment are (a control is used to minimize the unintended influence of other variables on the same
system):
5. The key concept(s) or theory (ies) behind the experiment is (are) (define terms like density, mass, volume, displacement, etc. can
you explain the relevant theory):
6. The important technique(s) used in this experiment is(are):
Please describe:
1. The experiment is based on the following assumptions (identify your assumptions and determine if they are justifiable):
2. The data that will be collected in the experiment are (what do you plan to record in your notebook)
3. The potential consequences of the experiment are:
4. The point of view behind the experiment is (make sure it’s scientific).
5. What special safety precautions do you need to be aware of for this experiment?
MEASURING DENSITY
Purpose:
The purpose of this experiment is to learn to measure the mass of an object using a simple electronic balance, to learn to deliver precise
volumes using a pipet, to carry out calculations involving density, and to perform error analysis on experimental measurements.
Special Apparatus and Chemicals:
Thermometer
10 mL Pipet
Rubber stopper or cork
Unknown liquid
Unknown solid
Discussion:
Before beginning this experiment, you should be familiar with how to carry out error analysis with laboratory measurements. Specifically,
you should be aware of the difference between accuracy and precision, know how to work with and determine significant figures, and
know how to calculate averages, average deviation, and standard deviation. If you are unfamiliar or unsure about any of these topics you
should read “Error Analysis”, “Significant Figures”, and “Statistical Methods” in the Mathematical Methods section of this manual. Also
before beginning this experiment you should read through the “Measurement of Mass” and “Measurement of Volume” in
the Experimental Techniques section of this manual.
In carrying out an experiment, a scientist makes observations (qualitative) and measurements (quantitative). With any measurement
there is a certain amount of error. Some error will be random error due to pushing measurements to their limit. Some error will be
systematic leading to consistent deviations from a true value due to a definite mistake, procedural error, or inaccuracy of the equipment.
Two of the most common measurements that you will make in general chemistry are measurements of mass and volume. Mass can be
measured using an electronic balance which depending on the model may have a limit of precision (and therefore maximum accuracy) of
+0.01 to +0.0001 grams. Check with your instructor to find the limit of precision for the balance you will be using. Remember when
making measurements always record all digits available. For example, the mass of an object weighed on a balance with a +0.001 grams
limit of precision should be recorded to 3 decimal places in grams. Volume may be measured with a variety of devices: beakers,
graduated cylinders, burets, and/or pipets, depending on the desired precision. The most precise device for measuring volume is a
volumetric pipet. A 10 mL volumetric pipet has a +0.01 mL limit of precision if used properly.
In this experiment you will check the calibration of the electronic balance and then use the balance to check the precision of your
pipetting technique. You will then determine the density of an unknown solid and an unknown liquid.
Group Experimental Design Pre-lab
1. Design two experiments to determine the density of the object, using the limited resource available to you, including a balance, some
volumetric equipment such as graduated cylinder, Erlenmeyer flask, beakers, rulers, etc. Hint: What are some ways scientist can
determine the volume of an object?
2. Write a detailed experimental procedure. This procedure should be written stepwise with the initials of the student who is performing
that step in the procedure. Here is an example:
1. Weigh substance- AW (these are the initials of student performing task)
2. Get the volume of substance – EE
3. etc.
TABLE I: Density of Laboratory Solvents and Solutions at 20°C (g/mL)
Acetone
0.7899
Hexane
0.6603
Cyclohexane
0.7785
Ethanol
0.7893
Toluene
0.8669
Ethanol 95 %
0.8056
Water
0.9982
Ethanol 50%
0.9139
7% NaC1
1.0486
2-Propanol
0.7848
For solids and liquids density changes slowly with temperature. The density of water at room temperature is close to 1.00 g/mL. This is a
result of a gram being originally defined as the mass of one cubic centimeter of water. The table below gives density of water at various
temperatures to four decimal places. A more complete table may be found in Appendix C.
TABLE II: Density of Water at Various Temperatures
Temperature
Density (g/mL)
Temperature
Density (g/mL)
20°C
0.9982
24°C
0.9973
21
0.9980
25
0.9970
22
0.9978
26
0.9968
23
0.9975
27
0.9965