# Conversions _Dimensional Analysis_ by pptfiles

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```									Grams→Particles
Grams→Particles
How many formula units are there in 24 grams of FeF3?

24 g FeF3

the known
quantity
Grams→Particles
How many formula units are there in 24 grams of FeF3?

24 g FeF3 x
g FeF3

Starting unit
must be in
the known
the
quantity
denominator
to cancel it
out
Grams→Particles
How many formula units are there in 24 grams of FeF3?

1 mol FeF3
24 g FeF3 x
112.8 g FeF3

the known        112.8 g FeF3 is equal to 1 mol FeF3
quantity          (it’s the molar mass of FeF3)
Grams→Particles
How many formula units are there in 24 grams of FeF3?

1 mol FeF3
24 g FeF3 x
112.8 g FeF3

the units of “g FeF3”
cancel out
Grams→Particles
How many formula units are there in 24 grams of FeF3?

1 mol FeF3
24 g FeF3 x              x
112.8 g FeF3   mol FeF3

mol FeF3 is not desired, so it
must be in the denominator to
cancel it out
Grams→Particles
How many formula units are there in 24 grams of FeF3?

1 mol FeF3
24 g FeF3 x              x
112.8 g FeF3   mol FeF3

the units of “mol FeF3”
cancel out
Grams→Particles
How many formula units are there in 24 grams of FeF3?

23
1mol FeF 3     6.02 x 10 f.u. FeF3
24 g FeF x
3                x
112.8 g FeF 3       1mol FeF 3

6.02 x 1023 f.u. FeF3 are equal to 1 mol FeF3
Grams→Particles
How many formula units are there in 24 grams of FeF3?

1mol FeF       6.02 x 1023 f.u. FeF
24 g FeF x
3
3
x                     3
 1.28 x 1023 f.u. FeF3
112.8 g FeF 3       1mol FeF   3

24 x 1 x (6.02 x 10 23 )
 1.28 x 10 23

112.8 x 1
Grams→Particles

1mol FeF       6.02 x 1023 f.u. FeF
24 g FeF x
3
3
x                     3
 1.28 x 1023 f.u. FeF3
112.8 g FeF 3       1mol FeF   3

Another way to write this…

24 g FeF     1mol FeF       6.02 x 1023 f.u. FeF
3            3                          3
 1.28 x 1023 f.u. FeF3
112.8 g FeF3        1mol FeF   3
Grams→Particles

It’s called a “fence post” method or “t-chart” by some. In
place of an “x” sign, vertical lines are used to separate
parts of the calculation

24 g FeF     1mol FeF      6.02 x 1023 f.u. FeF
3            3                         3
 1.28 x 1023 f.u. FeF3
112.8 g FeF3       1mol FeF   3

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