Video Transcript
Which of the following best
describes the quantity that has the unit “mole”? (A) The number of equivalent parts
that an object made of a substance consists of. (B) The amount of a substance that
is contained in an object.
This question is asking us about
what a mole is in terms of scientific units. A mole is a base SI unit and refers
to the total amount of a substance. This could make us think that the
answer is (B) because it leads us to believe that mole refers to the amount of a
substance contained in an object. But this is not the correct
definition, because a mole refers to a substance made up only of equivalent parts
like atoms or molecules.
A statement as vague as “an amount
of substance in an object” could reasonably refer to other units, like volume. So, let’s clarify what makes moles
special. Recall that in the SI system, the
base unit of mole refers to a specific number of equivalent parts. This number is 6.02214076 times 10
to the 23, usually shortened to 6.022 times 10 to the 23.
One mole of a substance refers to
an object containing this number of equivalent parts. This is the well-known Avogadro
number, named after the physicist and chemist Amedeo Avogadro.
As an example, let’s consider some
water. In one mole of water, there are
6.022 times 10 to the 23 total H2O, or water, molecules. Each individual water molecule is
made up of two hydrogen atoms and one oxygen atom. This means if we were to look at
the atoms that make up our one mole of water, we would find that there are two times
6.022 times 10 to the 23 hydrogen atoms, that is, two moles of hydrogen atoms, and
6.022 times 10 to the 23 oxygen atoms, one mole of oxygen atoms.
Usually only atoms and molecules
are counted in moles, given how big the number is. So, when we use moles, we are not
just looking at some amount of a substance, we are looking at a highly specific
number of atoms or molecules that an object consists of, which are all equivalent to
each other. Based on this, it is safe to say
that option (A) would be the most correct answer.
So, the answer to which statement
best describes the quantity that has the unit mole is option (A): the number of
equivalent parts that an object made of a substance consists of.
