The graph shows how the values of one variable quantity depend on the other variable quantity. The variable quantities in this case are concentration and absorbance.
Dependent variable: Plotted on the y-axis (absorbance in this case because absorbance depends on concentration)
Independent variable: Plotted on the x-axis (concentration in this case - concentration does NOT depend on absorbance)
The scale for each axis should be chosen so that your
graph occupies most of the page as shown for the calibration graph below.
Concentration/
| Absorbance
at 650 nm |
| 0.000 | 0.000 |
| 0.0100 | 0.110 |
| 0.0200 | 0.200 |
| 0.0600 | 0.660 |
| 0.0800 | 0;.920 |
Set 2 absorbance concentration graph
Each
axis should be
labelled with the name and
unit of the variable and
any factor by which all values for that axis have been divided before plotting.
What is the factor? It is convenient to plot numbers between 0.01 and 100. The factor by which the numerical values are divided before plotting must be appropriate to the data.
The
concentrations in the data shown are
divided by 0.01 because this make the x-coordinate of these points are between 1 and 10.
When the data are read from the graph, they must be multiplied by the factor and its unit before using them in calculations.Thus, in this example,
any x-coordinates read
from the graph are
multiplied by 0.01 to convert them to the concentration values.
Lines of
best fit are drawn if it is known that the two variables are linearly related.
If 0,0 is a valid data point, the line should be oriented so that it goes through this point. In general the best fit line should be oriented so that it has as many of the experimental points above the line as below line.