Density
Introduction:
In this lab you will have the opportunity to use the electronic balances, graduated cylinders, and
volumetric pipettes to determine the densities of different liquids and solids using a variety of
techniques.
During this experiment, focus on using the proper number of significant figures in all of
your measurements and in
ALL
of the calculations.
Background:
Density is calculated by dividing a mass by a volume, as shown below in Equation 1.
Equation 1:
m
D =
V
Although the “proper” SI unit for density is kg/m
3
, in chemistry, the unit that we generally use to
measure mass is the gram (g); volumes of solids and liquids are measured in cubic centimeters (cm
3
) or
milliliters (mL).
Therefore, your units for density are either g/cm
3
or g/mL. Since one milliliter is equal to
one cubic centimeter, 1 g/cm
3
is equivalent to 1 g/mL.
Determining the Density of a Liquid:
A container must be used to hold the liquid that you wish to weigh.
This container will either need to be
preweighed to determine its mass.
Next, the liquid is added to the container and the combined mass is
determined.
A simple subtraction yields the mass of the liquid.
To obtain the volume of the liquid, an accurate measuring device is required.
This could be either a
graduated cylinder or a pipette (but not a beaker!).
When using the graduated cylinder, keep in mind
that it should be read as accurately and precisely as possible.
Before you start, look at the graduated
cylinder and decide what your “best guess” is for that particular cylinder.
Then, making sure you are at
eyelevel with the level of the liquid, read the very bottom of the meniscus (the meniscus is the curve or
arcshaped appearance of the water).
A second method is to use a volumetric pipette.
If the pipette is
filled to the correct mark (that is – bottom of the meniscus again), it will deliver a precise and specific
volume of that liquid.
Determination of the Density of a Solid:
To obtain the mass, simply weigh the object on the scale.
Some solids may need to be weighed in a
weighing boat or a beaker – if this is the case, then remember to account for the mass of the object
used to hold the solid.
To obtain the volume of the solid, one of the two following procedures should be selected based on the
appropriateness.
If the object has a uniform shape with measurable dimensions, then it is possible to
use a ruler to find the volume.
Simply measure the dimensions in centimeters and apply the
appropriate formula.
If the object is irregularly shaped, then the displacement method must be used.
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 Fall '09
 Electron, Density, Lab Activity

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