Chemistry Reference
In-Depth Information
As you begin your laboratory work in chemistry, it is likely that you will be
asked to find the mass, volume, and density of substances early on.
The volume of a substance is simply the amount of space that it takes up
(in other words, how big it is). The standard method for measuring the
volume of a substance depends upon whether or not the substance is a
solid, liquid, or gas.
Your laboratory will include several types of vessels that can be used to
measure the volume of a liquid. The most accurate measurements can be
taken in a vessel called a graduated cylinder, or “graduate,” for short.
Graduated cylinders come in many sizes, and the accuracy of these instru-
ments depends upon the number of lines or gradations on them. Usually,
the smaller graduates are more accurate than the larger ones, and all gradu-
ates tend to give more accurate readings than beakers or flasks.
When you need to find the volume or size of a solid, the method that
you choose will depend upon whether or not the solid has a regular shape.
For example, if you need to find the volume of a uniform block, you can
measure the length, width, and height of the object, and then multiply them
together using the formula: volume = length × width × height.
If you need to find the volume of a solid that is not a regular shape, you
can often use what is called the “water displacement method.” Imagine
that we wanted to find the volume of a nail. A nail isn't close enough to a
perfect cylinder to consider using the formula for the volume of a cylinder,
so how would we measure its volume? We would make use of a real cylin-
der, a graduated cylinder. How can we find the volume of a solid in a vessel
that is made to measure the volume of a liquid? We could, theoretically,
melt the nail, but we would have to get it too hot and the process would
change its volume slightly. We have to come up with another plan.
Have you ever poured a glass of water or soda, and then added ice
cubes? Did you ever add enough ice to make the level of the liquid over-
flow from the glass? This happens because the ice takes up space, and in
order for it to fit in the glass it pushes some of the liquid out. Solids take up
space, and they will displace liquids that they are submerged in.
Take a graduated cylinder, fill it with some measurable amount of water,
and record this volume. Next, carefully place the nail into the graduate, and
the water level will rise. In order to be accurate, the nail must be completely
submerged. Now, record the new volume. The volume of the nail will be the
difference between the two water levels. Look at the formula here:
v
f
- v
i
= v
nail
volume final - volume initial = volume of the nail
