Data tables and plotting Lab data

CHM 2045L Lab 2: Data Tables and Plotting Lab Data

Objectives:

Learn how to make a data table.

Learn how to plot lab data, including titles, labels, and best-fit straight line.

Data Tables:

When making data tables, the following are required:

Title: A few words to briefly describe the type of information in the table. If more than 1 table is

present, number the tables. For example,

Table 1. Data for Lab 4: Determining the formula for a compound.

Table 2. Summary %Cu and %Cl in copper chloride compounds.

The 1st row of the table should be a header row and contain titles for each column. If there are units

associated with the values, include those in parentheses. When possible, try to not to have tables spread

over 1 page. For large tables this may not be avoidable, in which case make sure to include the header

row at the top of the table on each page.

Plotting Data (also known as Graphing Data):

When graphing scientific data, there are several things that must be included in addition to plotting the

data points, such as a title and axes labels including any applicable units. In this lab we will cover the

basics of what is required for graphs you will be making in this and subsequent chemistry labs.

When plotting data points, typically the 1st column is the value for the x-axis (horizontal axis) and the 2nd

column is the value for the y-axis (vertical axis). Some lab data may require they be switched so that the

slope of the best-fit data line gives a desired result. For example, plotting mass on a y-axis and volume on

an x-axis would result in a slope that gives the density of the substance.

Every graph or plot should have a title that clearly states what type of data is being shown. In axes

should also be labeled with what is being measured as well as the units used to measure. For example, an

axes may be labeled volume (in mL) or as volume, mL. Both ways are acceptable and are often used.

After data points are plotted, it’s often necessary to find the best-fit straight line. This should be a

straight line that is drawn as close to the points as possible and usually doesn’t not include all of the data

points. Figure 1 shows an example of a best-fit straight line.

Figure 1. Sample best-fit straight line.

Equation for a best-fit line: A line has the equation:

y=mx+b

where:

y = vertical axis value (also known as the ordinate)

x = horizontal axis value (also known as the abscissa).

m = slope, which may be found using x and y values from 2 places on the best-fit straight line.

Ideally these 2 places on the line should not be close together. Slope = (y2-y1)/(x2-x1). The

units of the slope depend on the units of the y- and x-axes.

b = y-intercept (the value of y where x=0).

0

20

40

60

80

100

120

0 50 100 150

V
o

lu
m

e
(

m
L)

Pressure (mm Hg)

Sample Data Plot

Name: ___________________________

Procedure: For each of the following sections, follow the directions to graph the data. The graphs and

answered questions will count as your lab report for this lab. Each student must turn in their own graphs

and answers to the questions. You must do the graph for #1 by hand using graph paper, a ruler, and

calculator. For #2 and #3 you may either do them by hand or using a spreadsheet like Excel, but you

1. Given the following data from a gas experiment measuring changes in volume in response to

increasing the temperature:

Data for #1.

Temperature (oC) Volume (L)

20.0 1.61

40.0 3.30

55.0 5.44

70.0 5.75

85.0 6.99

100.0 8.25

150.0 12.29

a. Plot the points on a graph.

b. Draw a best-fit straight line.

c. Calculate the slope.

d. Calculate the y-intercept.

e. At what temperature would the volume = 1.50L?

f. At what volume would the temperature = 125.0 oC?

g. What is the equation for the line?

2. Given the following data, graph mass vs. volume so the slope will give the density of the

substance.

Data for #2.

Volume (mL) Mass (g)

0.50 4.00

1.00 7.82

1.40 10.98

2.00 11.6

2.80 22.0

3.81 30.1

a. What would the volume be at 25.0g?

b. Draw the best-fit straight line and write the equation for the line on the graph.

c. What is the slope of the graph?

d. Using the table at the end of this lab to identify the metal.

3. Given the following non-linear data, plot pressure along the y-axis and 1/volume along the x-axis.

Data for #3.

Volume (mL) Pressure (torr)

42.6 400

34.1 500

28.3 600

24.4 700

21.2 800

19.0 900

17.1 1000

15.4 1100

14.2 1200

a. Draw the best-fit straight line.

b. Write the equation for best-fit straight line.

c. What is the slope of the line?

Table of metallic densities for #2.

Element
Density

g/mL

Aluminum 2.70

Antimony 6.68

Barium 3.62

Brass 8.55

Bronze 8.20

Chromium 7.15

Copper 8.96

Gold 19.3

Iron 7.87

Magnesium 1.74

Nickel 8.90

Platinum 21.5

Rhodium 12.4

Silver 10.5

Tin 7.26

Titanium 4.51

Tungsten 19.3

Zinc 7.14

Zirconium 6.52