Unit 1, Lab 1: Graphical Determination of Density

Background:

Density is mass per unit volume. The mass of any material divided by the volume of the sample, or the space it occupies, will give the density of that material. A good scientist would not be satisfiedwith a value based on one set of measurements; it is more accurate when the value is found by averaging the results of several experiments. Another approach is the use of a graphical method to find an average value. The purpose of this experiment is to determine the density of water by both conventional and graphical methods. Students will graph significant digits in making measurements and in calculations. Students will graph a series of laboratory measurements and determine density from a mass vs. volume graph.

Reactions and Equations:

Density = mass/ volume

Equipment and Reagents (Safety):

50mL graduated cylinder

pipet

30mL beaker

Balance

Water

Spreadsheet software (Excel)

*While there are no inherent safety concerns with materials being used, please work to avoid overcrowding which can lead to broken glassware.

Procedure:

Work in teams of two, please work to complete the following procedure:

**Pay attention to significant figures and the proper recording of measurements**

  1. Obtain a clean, dry graduated cylinder. If you are unsure of how clean the piece of glassware is, wash it with soap and water and make sure it is completely dry. Obtain the mass of the graduated cylinder and record.
  2. Carefully remove the graduated cylinder from the balance and add 10mL of water to the graduated cylinder. Record the mass of the water plus graduated cylinder.
  3. Follow step two adding an additional 10mL of water to your graduated cylinder until you have added a total of 50mL to the cylinder.
  4. Dispose of the water in the sink, dry your glassware and store it in your lab drawer.
  5. Share your data with your lab team and record their data in the other columns of your data table.

Data and Observations:

Create a table in your lab notebook similar to the one below in order to neatly record your data. Do not forget to make the table with a ruler and record all appropriate observations. You should have two tables: one for you and your partner’s data and one for the other people at your bench.

Trial / 1 / 2
Mass of graduated cylinder (g)
Mass of graduated cylinder and 10mL of water (g)
Mass of graduated cylinder and 20mL of water (g)
Mass of graduated cylinder and 30mL of water (g)
Mass of graduated cylinder and 40mL of water (g)
Mass of graduated cylinder and 50mL of water (g)

Treatment of Data:

  1. For each trial, subtract the initial mass of the graduated cylinder from the total volume of water + graduated cylinder. Record the resulting values for the mass of water vs. volume of water.
  2. Mathematically calculate the density of water for each of the 5 volumes of water used.
  3. Using EXCEL, plot the mass of the water on the y- axis and the volume of the water on the x-axis. Insert a trend line.
  4. From the equations of the trend line, record the slope of the line. What is the slope equal to?????

Post Lab Questions:

1.)How does the density from your own trial compare with the average density found from the slope of the plot?

2.)How many significant digits did you record in the density calculated for your trial? Explain how you decided on the number of digits.

3.)Calculate your percent error.

4.)How could the experiment be changed to decrease the experimental error? Suppose you wanted to use a graphical method to find the number of miles your car can travel on a gallon of gasoline. Briefly describe a procedure you could use.