Reading: Graphing Techniques
Revised 1/14/10
1
GRAPHING TECHNIQUES
Mathematical relationships between variables are determined by graphing experimental data.
For example, the linear relationship between the concentration and the absorption of dilute
colored solutions leads to Beer’s Law (A=
C
l
).
Once the mathematical relationship is known,
experimental quantities can often be calculated from the slope or yintercept of a graph.
For
example, reaction enthalpy can be determined from the slope of a plot of ln k vs. inverse T.
Furthermore, extrapolation of graphical data trends can be used to find information about
conditions difficult to achieve in the laboratory, such as high or low temperatures and pressures.
Plotting Variables
A line graph consists of two axes at right angles.
The horizontal
xaxis
, or
abscissa
, is typically
chosen to represent the
independent
variable which is intentionally manipulated by the
experimenter.
The vertical
yaxis
, or
ordinate
, is chosen to represent the
dependent
variable
which changes as the independent variable is manipulated.
Example:
A student wishes to measure the relationship between volume and temperature of a
gas.
If the student purposely increases the temperature and measures the resultant changes in gas
volume, he should graph the values for T on the xaxis and the resulting values for V on the y
axis.
If the student reverses the experiment and purposely increases the volume of the gas and
measures the resultant temperature, the variables are then reversed:
V is plotted on the xaxis
and T is plotted on the yaxis.
Selecting a Title and Labeling the Axes
The title must describe the type of reaction or system being investigated, chemicals used, and
special conditions of the experiment.
Examples:
"Beer’s Law Plot for Co(NO
3
)
2
(aq) at 510
nm" or "Cooling Curve for Lauric Acid/Unknown Mixture".
Do not state x vs. y in the title
, that
is easily determined by labeling the axes.
Axes must be labeled with the name (or symbol) of the
variable and include the units (if any).
Examples:
Temperature (°C) or V (mL).
This preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentReading: Graphing Techniques
Revised 1/14/10
2
Choosing an Appropriate Scale
The scale of the graph should be chosen so the data completely fills the graph and is not
restricted to one small region or corner.
Examples are shown in Figure 1.
Note that the scale
This is the end of the preview.
Sign up
to
access the rest of the document.
 Spring '10
 Dr.KimberlyEdwards
 Cartesian Coordinate System, pH, line graph, data points

Click to edit the document details