Unit Conversion and Mole Concept in Chemistry
Unit Ten:
Introducing the Mole
What’s a mole?
The
mole
is a unit of
measure
.
Just like meters tells us
length
and seconds tells us how much
time
,
the
mole
measures an
amount
(how much).
Units of measure similar to mole include:
Dozen =
12
Ream =
500
Mole =
6.02 x 10
23
Ted ed video:what is a mole
Why do chemists use the mole?
•
The unit mole is based on
Avogadro’s number
which is equal
to
6.023 x 10
23
.
•
This number is very, very
large
.
•
Atoms and molecules are very, very
small
.
•
Since the atoms and molecules are
very small
, we need
a very
large
unit to describe them.
•
For this reason, the unit
mole
is mostly used in chemistry.
How small is an atom?
How many moles of chalk does it take to write your name?
_____ g chalk
(CaCO
3
)
I mole
________atoms
__________ g CaCO
3
1 mole
Unit Conversions
:
•
Unit conversions (dimensional analysis) allows us to compare two
separate units of measure by using a conversion factor.
•
Example: 2 dozen eggs = ? Eggs
12 eggs
=
__
X
___
1 doz.
2 doz.
here’s the math: 2 dozen x
12eggs
= 24 eggs
dozen
[12 eggs/dozen] is the
conversion factor
that lets us compare eggs & dozen
Unit Conversion & dimensional analysis
•
Set up to cancel units:
2 dozen
x
12eggs
=
24 eggs
dozen
This set up allows us to make many comparisons in one calculation:
Ex: Convert 12 days to seconds: 12 days x
24 hrs.
X
60 min.
X
60 sec
= 1036800 sec.
1 day 1 hr.
1 min
Unit conversion and dimensional analysis:
•
Determine the final label by crossing out the units that cancel:
•
1)
mi
x
hr
x
min
x
m
x
cm
=
hr
min s mi m
•
1)
mi
x
hr
x
min
x
m
x
cm
=
cm
hr
min s mi m s
Unit Conversions:
•
Convert 3.0 centimeters to feet
Strategy: cm
inches
feet
3.0 cm
x
1 in
x
1 ft
=
2.54 cm 12 in
Molar Mass Conversions
:
•
The unit mole now allows us to relate
mass
to
atoms and
molecules
.
•
This is important since atoms and molecules are so
small
,
we can use the unit mole to obtain tangible
measurements
.
•
Molar mass describes how many grams in one mole of an
element or compound. It is a
conversion factor
between
grams
and
moles
.
Molar Mass Conversions
:
1.
Molar Mass
describes how many grams in one mole of an element
or compound. It is determined just like
formula mass
. We add the
mass of all the contributing elements. This information is found on
the
periodic table
.
2.
When converting mass to moles we
divide
by the molar mass.
3.
When converting moles to mass we
multiply
by the molar mass.
Molar mass conversions:
•
Calculate the
molar mass
of sodium hydroxide (NaOH)
Na = 23.0g
O = 16.0g
H =
1.0 g
40.0 g/mole
Convert 226g of NaOH to moles:
Convert 1.4 moles of NaOH to grams:
Convert 28.0 grams of NaOH to moles:
the Mole Road:
•
Grams
Moles
Find the number of moles in 92.2 g iron
•
Moles
Grams
Calculate the mass, in grams, of 0.250 moles of sodium.
•
Moles
Atoms
Calculate the number of atoms in 3.2 moles of carbon
•
Grams
Atoms
Calculate the number of atoms in 2.5 grams of silver.
Explore the concepts of unit conversion and the mole in chemistry, including how to convert between different units, relate mass to atoms and molecules, calculate molar mass, and perform conversions involving substances like chalk and sodium hydroxide. Discover the importance of dimensional analysis and the molar mass in chemistry calculations.
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Presentation Transcript
How small is an atom? How many moles of chalk does it take to write your name? _____ g chalk (CaCO3) I mole ________atoms __________ g CaCO3 1 mole
: Unit conversions (dimensional analysis) allows us to compare two separate units of measure by using a conversion factor. Example: 2 dozen eggs = ? Eggs 12 eggs = __X___ 1 doz. 2 doz. here s the math: 2 dozen x 12eggs = 24 eggs dozen [12 eggs/dozen] is the conversion factor that lets us compare eggs & dozen
Unit Conversion & dimensional analysis Set up to cancel units: 2 dozen x 12eggs = 24 eggs dozen This set up allows us to make many comparisons in one calculation: Ex: Convert 12 days to seconds: 12 days x 24 hrs. X 60 min. X 60 sec = 1036800 sec. 1 day 1 hr. 1 min
Unit conversion and dimensional analysis: Determine the final label by crossing out the units that cancel: 1) mi x hr x min x m x cm = hr min s mi m 1) mi x hr x min x m x cm = cm hr min s mi m s
Unit Conversions: Convert 3.0 centimeters to feet Strategy: cm inches feet 3.0 cm x 1 in x 1 ft = 2.54 cm 12 in
: The unit mole now allows us to relate mass to atoms and molecules. This is important since atoms and molecules are so small , we can use the unit mole to obtain tangible measurements. Molar mass describes how many grams in one mole of an element or compound. It is a conversion factor between grams and moles.
: 1. Molar Mass describes how many grams in one mole of an element or compound. It is determined just like formula mass. We add the mass of all the contributing elements. This information is found on the periodic table. 2. When converting mass to moles we divide by the molar mass. 3. When converting moles to mass we multiply by the molar mass.
Calculate the molar mass of sodium hydroxide (NaOH) Na = 23.0g O = 16.0g H = 1.0 g 40.0 g/mole Convert 226g of NaOH to moles: Convert 1.4 moles of NaOH to grams: Convert 28.0 grams of NaOH to moles:
Grams Moles Moles Grams Moles Find the number of moles in 92.2 g iron Grams Calculate the mass, in grams, of 0.250 moles of sodium. Atoms Calculate the number of atoms in 3.2 moles of carbon Atoms Calculate the number of atoms in 2.5 grams of silver.
