>> narrator: In this
Closer Look, we'll focus
on converting from moles
to particles.
As a reminder,
a mole is really big number--
6.02 times 10 to the 23rd,
sometimes referred to as
Avogadro's number.
The particles in the conversions
can be either atoms
or molecules.
When doing these calculations,
use this conversion factor.
The numerator
in the conversion factor is
6.02 times 10 to the 23rd,
which could be atoms,
molecules, or formula units.
And the denominator is
one mole of the substance
we are converting.
When doing conversions problems,
remember, take the number
you are given in the problem
and put it in
the upper left hand corner
of the conversion chart.
For this problem,
there are 3.51 moles
of sodium given.
The next step is to
bring the units down,
so put moles of sodium
in the denominator
of the second column.
And one mole of sodium
is the same as
6.02 times 10 to the 23rd
sodium atoms.
So I will write that
in the numerator.
Notice that the units
of moles of sodium cancel,
leaving atoms of sodium,
which is what you are
solving for.
All that's left to do
is to multiply
3.51 times
6.02 times 10 to the 23rd.
If there are numbers
other than one
in the denominator,
divide those numbers,
but in this problem
there is only a one.
So, 3.51 times
6.02 times 10 to the 23rd
will give us the number
of sodium atoms.
And the result is 2.11
times 10 to the 24th.
That's how many atoms
of sodium there are
in 3.51 moles of sodium.
This next problem
involves converting from
moles to molecules of water.
"How many molecules
"of water are there
"in 2.75 moles of water?"
Since molecules
are very small,
they are considered
representative particles,
so solve this problem
in a similar way
to the last one.
Take what's given,
2.75 moles of water--
put that in
the upper left hand corner
of the conversion chart,
bring down the unit.
Moles of water
in the denominator
of the second column.
And one mole of water
is the same thing as
6.02 times 10 to the 23rd
molecules of water.
Again, notice the moles
of water cancel, because
they appear in both
the numerator
and the denominator.
The unit that is left
is molecules of water,
which is what
you're solving for,
so all that is left to do
to get the answer
in molecules of water
is to multiply 2.75 times
6.02 times 10 to the 23rd.
And when 2.75
is multiplied by
6.02 times 10 to the 23rd,
you get 1.66 times
10 to the 24th
molecules of water.
That's the same thing
as 2.75 moles of water,
and that is the answer
you are looking for
when converting
moles of water
to particles of water.
Here's one for you to try.
"How many molecules
"of carbon dioxide are there
"in a sample of 0.75 moles
"of carbon dioxide?"
When you're ready,
press pause,
try to solve the problem.
And when you think
you have it, press play
and check your answer.
Let's see if
you got it right.
This is how your set up
should have looked:
0.75 moles of carbon dioxide,
placed in
the upper left hand corner.
Then, you should have
brought the units down,
to convert from the moles
of carbon dioxide
to molecules
of carbon dioxide.
The units cancel
because they appear
in the numerator
and the denominator,
so moles of carbon dioxide
go away,
and all that is left to do
is multiply 0.75 times
6.02 times 10 to the 23rd,
to determine
how many molecules of
carbon dioxide there are.
And when you multiply
those two together,
you get 4.5 times
10 to the 23rd molecules
of carbon dioxide.
That is the same amount
of carbon dioxide you have
in 0.75 moles
of carbon dioxide,
so you converted that
into molecules.
That's a Closer Look
at Converting Moles
to Particles.
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