Determining Density from Graphs
• Density is defined as the mass of a certain
volume of a substance.
• Therefore, we can determine the density
from experimental measurements of mass
and volume
Graphing Terms
• Independent Variable - the variable that is
manipulated as part of the experiment
•
placed on the x-axis of the graph
• ** here, we manipulate the VOLUME of the
water.
• Dependent Variable - the variable that changes as
a result of the independent variable changing
•
placed on the y-axis (in this case, MASS)
• Slope - mathematical relationship between
variables on a linear graph
•
“steepness” of the graph
rise
slope =
run
m
recall : d =
V
• If volume is the independent variable (x
axis) and mass is the dependent variable (y
axis) then the slope of the graph will be the
density of the substance.
rise m
slope =
=
=d
run V
Example
• Several samples of a liquid are measured by
graduated cylinder.
• The mass of each sample is found.
• Graph the results with mass on the ‘y’ axis
and volume on the ‘x’ axis.
Sample Graph
Density
30
Mass (g)
22.5
Rise = 17.5 g
15
7.5
0
0
8
Run = 20.0 mL
15
Volume (mL)
23
30
Density
30
Mass (g)
22.5
Rise = 17.5 g
15
7.5
0
0
8
Run = 20.0 mL
15
23
30
Volume (mL)
rise 17.5 g
slope =
=
= 0.875 g/mL
run 20.0 mL
Density (from slope)
• From the graph, the density of the unknown
liquid would be:
• d = 0.875 g/mL