Chemistry, the branch of
Science involving the study of matter, is a quantitative subject. This means that
measurements and calculations involving matter are central to the subject at hand.
Matter is sometimes defined as "anything that has mass and volume."
Another definition of matter is "anything that has the property of
inertia." This lesson deals with some of the most basic and important concepts
of Chemistry, in that the concepts involved are necessary to understand the definitions of
matter.
Each time that you do a
laboratory activity this year you will be collecting data. Mass and volume are
probably the most common types of quantitative measurements that you will take, so it is
important for you to have a clear understanding of what you are measuring. When you
know the mass and volume of a substance, you can find its density. Weight is not
something that you will often have to worry about in Chemistry, but since many students
confuse the concept with mass, I will also explain weight here. The unit called The
Mole will also be introduced here.
Inertia - The inertia of an object
represents its ability to resist changes in its motion. This change in motion could
be in terms of speed, or in terms of direction. If you are in a car that stops
suddenly, you continue to move forward, because of your inertia. When a car makes a
sharp turn, you might feel yourself moving to one side, due to your inertia.
Mass - The balances that you use in
laboratory measure mass, not weight. Mass is sometimes defined as the amount of
matter in an object. 10.0 grams of gold would contain twice as many gold atoms as
5.0 grams of gold. Students sometimes confuse mass and volume because the term
"massive" can mean "large" in English. In Chemistry, mass has
nothing to do with size. The SI unit for mass is the kilogram (kg).
Conservation of Mass - One of the basic
scientific laws of Chemistry is called the Law of Conservation of Mass. The law
states that matter is neither created nor destroyed in an ordinary chemical reaction.
Now, it turns out that mass and energy can be converted into one another, in a
nuclear reaction, but (unless something goes horribly wrong) we will not be carrying out
any nuclear reactions in the Chemistry lab. This means that no matter what we do in
the Chemistry lab, the mass that we put into the reaction will be the same as the mass
that we get out of the reaction. In other words, in each chemical reaction that we
carry out in lab, the mass of the products will be equal to the mass of the reactants.
Volume - Volume is the amount of space
that an object takes up. When you buy a 2-liter bottle of soda, the soda takes up 2
liters of space. A 200 cm3 sample of gas is twice as large as a 100 cm3
sample of gas. The volume of liquids can be measured using graduated cylinders,
beakers and flasks. You can determine the volume of regularly shaped objects with a
meter stick. Objects that have an irregular shape are often measured through what is
called "the water displacement method." This means that you determine the
volume of the object by finding out how much water it displaces. In Chemistry we
often measure volume in milliliters (ml) or cubic centimeters (cm3). It
is important for you to know that milliliters and cubic centimeters are equivalent units,
so 1 ml = 1 cm3. There are 1000 milliliters in one liter.
Density - Density is the amount of matter in a
given unit of volume. It can be measured in grams per cubic centimeter (g/cm3).
It is a measure of how tightly packed the atoms of a substance are. When we
say that ice is less dense than water, we mean that the water molecules are more tightly
packed when they are in the liquid state. The formula for determining density is:
Submarines, scuba divers and many types of fish can alter their
depth in the water by adjusting their density.
Weight - Weight is a measure of the force of
gravitational attraction between two objects, one of which is usually the earth. The
weight of a certain object can change as it moves closer or further away from the earth.
On the moon, objects weigh about 1/6th of what they weigh on earth. Mass, on
the other hand, does not change with location. To gain or lose mass an object must
gain or lose atoms!
The Mole - As you might imagine, we will not be
able to measure the mass or volume of individual atoms or molecules in the Chemistry lab.
Molecules are so small that a single drop of water contains billions and billions
of them. Just like eggs are grouped in dozens, and other items are grouped in
grosses, atoms and molecules are grouped in moles. We may not be able to measure the
mass of one water molecule in lab, but we can measure the mass of one mole of water
molecules. In fact, one mole of water has a mass of 18.0 grams. How many items
make up a mole of items? 6.02 x 1023! A mole of helium atoms would
be 6.02 x 1023 atoms. A mole of carbon dioxide molecules would be 6.02 x
1023 molecules. Don't let the big number scare you. You will get
use to it!
Now, be sure to check out the worksheets
and the online
quizzes!
