+1 862 207 3288 Introduction: Connecting Your Learning
This laboratory exercise involves demonstrating an understanding of working with basic scientific measurements and being able to express data
and results in standard scientific form. The “hands-on” portion of the Laboratory Activity involves finding the density of a cylindrical
object using two different methods of finding the volume of the object. The first method involves direct measurement of the object using a
metric ruler. The second method involves finding the volume using the water displacement method (described below). In addition, an
introduction to Excel, a spreadsheet program, is presented. Excel is used to create dynamic spreadsheets that organize and present scientific
data, perform calculations and present experimental results in an organized fashion.
Readings, Resources, and Assignments
Multimedia Resources None
Required Assignments Lab 2 (100 points)
Materials (Lab Kit) 1. Cylindrical cork
2. 100 mL graduated cylinder
3. Metric ruler
Materials (Student supplied) Balance (optional)
Focusing Your Learning
Lesson Objectives
By the end of this lesson, you should be able to:
1. Demonstrate knowledge of the SI System and CGS System of units.
2. Convert between various SI units.
3. Measure the volume of various objects.
4. Calculate the density of a substance.
5. Differentiate between precision and accuracy related to scientific data.
6. Construct a dynamic spreadsheet using Microsoft Excel.
7. Construct a Laboratory Report from a template using Microsoft Word.
Background Information
Much of the background information on the SI system of units is presented in Lesson 2 in the main course. The table below appears here as a
refresher.
Fundamental Measurement SI Standard Unit CGS U.S. or English
Mass Kilogram (kg) Gram (g) Slug
Length Meter (m) Centimeter (cm) Foot
Time Second (s) Second (s) Second (s)
Temperature Kelvin (K) Celsius (oC) Fahrenheit (oF)
Quantity Mole (mol) Mole (mol) Mole (mol)
Electric current Ampere (A) Ampere (A) Ampere (A)
Luminosity Candela Candela Candela
Converting Areas and Volumes
Converting areas and volumes requires that the units as well as the numbers are either squared (area) or cubed (volume). Recall that two
squared (i.e. 22) is the product of 2 times 2 = 4. If finding the area of a rectangle that measures 2 cm by 3 cm, the area is (2 cm)∙(3 cm) =
6 cm2. This quantity would be read as “six square centimeters.” There are 2.54 centimeters in one inch. How many square centimeters are in
one square inch? The answer is NOT 2.54 cm2. The number 2.54 must be squared, as well as the units.
There are (2.54 cm)∙(2.54 cm) = 6.45 cm2 in 1 in2.
Example: Convert an area of 1 square foot to square centimeters.
1 ft2 x 122in2 x 2.542cm2 = 929 cm2
1ft2 1in2
Notice the units cancel just like numbers in the numerator and denominator of a fraction. The only unit that did not cancel was cm2 and that
is the desired unit for the answer. Conversion factors need not be memorized. Therefore, they will be provided to you or you can look up the
conversion factors in a table. Scientists just need to know how to use conversion factors.
The same idea can be extended to convert volume units. How many cubic centimeters are in a cubic inch?
1 in3 x 2.543cm3 = 16.4 cm3
1in3
Volume measurements for small solids are usually given in cubic centimeters (cm3) whereas liquid volume is usually given in milliliters (mL).
A useful conversion to remember is that 1 mL = 1 cm3.
Volume of a cylinder
The volume of a cylinder is found by finding the area of the circular base of the cylinder (π R2) and multiplying by the height of the
cylinder (h).
Example: The diameter of a cylindrical object is 22.1 mm and the height is 45.5 mm. Find the volume of the object.
First, convert the measurements to cm. 22.1 mm = 2.21 cm and 45.5 mm = 4.55 cm. The radius of the object is one half the diameter.
V = πR2h = (3.14) ∙ (1.105 cm)2∙ (4.55 cm) = 17.5 cm3.
Water displacement method for finding the volume of a solid
The water displacement method assumes that when an object is placed in a fluid (like water), the change in the volume of the fluid is equal
to the volume of the object immersed in the fluid.
The change is volume in the graduated cylinder (Vfinal – Vinitial) after the object is immersed in the fluid is equal to the volume of the
object.
For the same object as in the example above, the change in the volume of the water in the graduated cylinder should be about 17.5 mL.
Remember, 1 cm3 = 1 mL
This volume can then be used to calculate the density of the object.
Density
Density is a ratio of the object’s mass to the objects volume. Density is independent of the amount of the substance because it is a ratio.
If the mass doubles, so does the volume; so an increase by a factor of two is seen in both the numerator and the denominator. Any increase or
decrease in the amount of substance is essentially cancelled.
Density = mass/volume. Suppose the mass of the object in the example above was 2.23 g.
The density (d) = 2.23 g/17.5 cm3 = 0.127 g/cm3.
Accuracy versus precision
Precision refers to how closely several measurements agree with one another. If two people measure equal quantities of water with a graduated
cylinder, they may make two different measurements. A 100-mL graduated cylinder is filled with water between the 5 and 6 mL marks. Observer A
estimates the level of water at 5.3 mL, while observer B estimates the level of water at 5.4 mL. If a 10-mL graduated cylinder, with marks at
0.1 mL intervals, is filled with the same amount of water, the water level may then fall between the 5.3 and 5.4 mL marks, allowing the
observer to estimate to the hundredths place. Observers A and B will then agree on the measurement to the tenths place even if they do not
agree on the estimated hundredths digit. The 10 mL graduated cylinder allows measurements that are more precise.
The example above illustrates that when making measurements, digits should be included to the limits of that instrument, plus one digit that
is estimated; this estimated digit is the digit of uncertainty. Hence, a graduated cylinder with marks at 1 mL intervals will result in
measurements to the tenths place. In this case, the ones place is known with certainty and the tenths place is estimated.
Keep in mind that precision in measurement does not always imply accuracy. Accuracy refers to how closely a measurement agrees with the “true
accepted” value. For example, if a 10-mL graduated cylinder with marks at 0.1 mL consistently gives readings that are 0.3 mL less than the
actual volume, the measurements may be precise but not accurate.
The precision of measurements is important when making calculations. Remember that calculations cannot be more precise than the measurements
from which they are drawn, and measurements are limited in precision by the instrument that is used. The rules of significant figures are
important because they ensure that calculated quantities are no more precise than the least precise measurement. This is necessary because
the last digit of a measurement is always estimated.
Considering the example above with the 10-ml graduated cylinder, observer A sees the measurement as 5.32-mL, while observer B sees it as
5.36-mL. Either observer A or observer B may be correct, but they cannot both be correct. It is not known for sure if either is correct, at
least beyond the 5.3-mL mark. Therefore, any calculations made with this measurement must be limited to the same level of precision.
Percent Error and Percent Difference
Error = accepted value – experimental value
When a known accepted value is available, the error is usually expressed as a percent error.
Percent Error = | accepted value – experimental value | x 100
accepted value
When the accepted value is not known and two experimental values are compared, then percent difference is used to compare how one
experimental value agrees with another.
Percent Difference = [ experiment value #2 – experiment value #1 ]
x 100 =
( experiment value #1 + experiment value #2 )
2
Notice that the accepted value is simply the average of the two experimental values.
Writing the Laboratory Report
There are many different formats for the preparation of laboratory reports. Some science courses (professors) require a laboratory report
that looks like an article ready for publication in a scientific journal. Some professors are more concerned with how the data is presented
and analyzed. Other professors prefer a hand-written report in a bound laboratory notebook. Some prefer laboratory reports that are processed
on a computer and turned in electronically. The point is, there are many different ways to report the results of a laboratory experiment. In
this class, the lab report will be submitted electronically using the guidelines set forth below.
Required information for the lab report:
1. Heading: Personal information including name, class, section number, and date.
2. Lab title: Write a title that describes the nature of the lab.
3. Purpose: Write a brief statement explaining the objective of the lab and how this objective is going to be accomplished.
4. Materials: List the materials required to duplicate the lab. Include chemicals and concentrations. Specific amounts are not required
in this section.
5. Procedure: Provide a summary of the steps used in the experiment. This does not have to include every minor step; but an intelligent
person should be able to follow the procedure if he or she wanted to duplicate the experiment.
6. Data: Record all data directly into a data sheet or Excel spreadsheet (whichever is applicable). Label all data using the correct
number of significant figures for any measurement you make. Include proper units. Use tables whenever possible. Neatness counts.
7. Calculations: Don’t confuse data with calculations. Calculations are manipulations of the data you collected. For each type of
calculation, show an example. Show the equation used and in a separate step, substitute the numbers used. If graphs are used, ensure all the
elements of a graph are present. Note: Data and calculations can be in the same section of the report as long as there is a clear distinction
between them.
8. Results: This section is very short and contains the results obtained from the calculations performed above. For example, if the
purpose of the lab was to find the density of an object, the results might be stated as the following: “The density of the object was found
to be 0.54 g/cm3.” Note the results must show the proper number of significant figures and contain units if applicable.
9. Discussion Questions: The labs will all include a number of discussion questions. You should answer these questions in complete
sentences. Make sure to write out the question, followed by your response. This section does not need to be in paragraph form but rather
should be a list of the questions with their answers.
10. Conclusion: This is perhaps the most import section in the report. This section includes your analysis of what happened in the
investigation. The three-paragraph model is appropriate for most labs, although there may be labs where another model is more appropriate. In
the three paragraph model:
a. Paragraph one contains a brief summary of the theory behind the experiment. Define key terms and explain important theories. If you
refer to other sources in this section, make sure you cite the sources correctly (see Reference section below).
b. Paragraph two contains a discussion of the results of the experiment. Error analysis is one of the most important aspects in a
physical science lab report. Be sure to distinguish between a careless mistake and an error that is the result of a measurement. Discuss
percent error if there is a known accepted value to make a comparison to or percent difference between two or more experimental results. Make
a best guess as to what factors may have contributed to the errors.
c. Paragraph three contains a concluding statement. Be creative and include responses to questions such as:
i. Did you meet the purpose of the experiment?
ii. Could you modify the procedure to make the lab work better?
11. References: Be consistent with the format used to cite references. APA is a commonly used style:
a. Book Example:
Giancoli, D.C. (2006). Physics (6th ed.). Upper Saddle River: Pearson Prentice Hall.
b. Journal article(retrieved from the Internet): Pierce, D. & Pierce, T. (2007). Effective use of demonstration assessments in the
classroom relative to laboratory topics. Journal of Chemical Education, 84, 1150. Retrieved August 5, 2007 from
http://jchemed.chem.wisc.edu/Journal/Issues/2007/Jul/abs1150.html
If there are any questions regarding the proper way to cite references, please ask. In addition to the lab reports, some labs may require the
use of spreadsheets and other computer tools. Excel is a tool that has many applications both in and out of the classroom.
Excel Spreadsheets
A spreadsheet is a very useful computer tool that can be used to record and display data. In addition, spreadsheets can be used to make
calculations that automatically update when changes are made to the data used in the calculation. The example below may be helpful in
constructing the spreadsheet for this Lab.
In the spreadsheet above, double click on the spreadsheet. Notice that data can be changed and the changes made are reflected in the
calculations. If the student is not familiar with Excel basics, there are Excel tutorials available on the Internet or ask your instructor.
Some basic Excel tips:
• Don’t mix numbers and text in the same cell (specify the units for the numbers in separate cells).
• Formulas placed in cells always start with an equal sign (=). In the example above, in cell B14, place = B7-B5. B14 contains 90.1, B5
contains 64.3. Whenever either of these data changes, the contents of cell B14 will reflect this change.
• Keep the data section of the spreadsheet separate from the calculation section.
• Design the spreadsheet to be easy to read.
• Format numbers to reflect the correct number of significant figures.
Procedures
1. Design an experiment that illustrates the determination of the density of a cylindrical object found in the Lab Kit.
2. Prepare a dynamic Excel spreadsheet to record data and perform the calculations necessary to find the densities and compute the
percent difference between them.
3. Make the necessary measurements that allow the calculation of the volume of the object by the two methods described above (i.e.,
direct measurement with a ruler and water displacement). Note: If there is no access to a balance (or scale) to measure the mass of the cork,
use 4.65 g for the mass.
4. Record this data in the Excel spreadsheet.
5. Write the Laboratory Report using the steps outlined above (steps 1-5 and 9-10) in Microsoft Word. Steps 6, 7, and 8 are placed in
the Excel spreadsheet and the spreadsheet is placed in the Word document.
Assessing Your Learning
You will complete your first full lab report for this lab. Include each of the 10 elements shown in the information above for the lab. Refer
to the Laboratory Report grading rubric prior to submitting the report.
Your instructor will use the following guidelines to score your lab report:
I. Introductory Information: Heading, title, purpose, materials and procedures (20 points)
II. Data, Calculations and Results (25 points)
III. Conclusions and Critical Thinking (25 points)
IV. Organization (20 points)
V. Use of Accurate Scientific Terminology and References (10 points)
Submission
Important information: Please follow the procedure below in the completion of your assignments.
Compose your responses to the questions in a word processing program. Run spell check. Review your work to make sure that you have completely
answered all questions.
To upload your Lab from this assessment you must first click on the “Browse” button. Now click on the “Browse” button once the File upload
window pops up. There should now be another pop up window, which will allow you to choose the location of the file you’re uploading. Select
your file and then press “Open”. You will now be taken back to the File upload window; once here click on the “Submit” button and then click
on the “Close” button. Once you’re back to your assessment window you can submit your assessment.
When you have finished, you will need to close the browser window to return to your course.
Upload your Lab 2.
Have You Met The Objectives For This Lesson?
Copyright © 2015 Rio Salado College. All Rights Reserved.
Water Displacement Data Ruler Method Data
Mass cork (g) 4.65 Diameter (cm) 1.5
Initial Volume (ml) 71 Height cork (cm) 5.3
Final volume (ml) 81
Pi 3.141592654
Water Displacement Calculations Ruler Method Calculations
Volume cork (ml) 10 Radius (cm) 0.75
Density Cork (g/ml) 0.465 Volume cork (cm3) 9.37
Density cork (g/cm3) 0.496483344
Percent difference 4.32
