Best Tips on Stoichiometry Conversions

In calculations involving Stoichiometry, there are certain Stoichiometry Conversions that one needs to get accustomed to.

There is need to know how to convert from one parameter to another quantity.

There are times you need to convert from mole to mass or mole to volume as the case maybe but understanding that these are interlinked is the fiat basic step in the conversions.

There is a need to understand. the basics of mole concept and stoichiometry and then be able to relate it to every other conversion you need to do.

What are the stoichiometry conversion factors?

In stoichiometry conversions, there is need to decipher the conversion factor of what you are trying to convert.

Mole vs Mass stoichiometry conversion

To convert mole to mass in Stoichiometry, you only need to recall the molar mass of the substance you want to convert to mole.

Conversion factor
1 mole of a substance = Molar mass of substance

Example 1
Convert 2.4 moles of magnesium chloride (MgCl2) to its mass.
First look up the mass of magnesium and chlorine in the periodic table.
1 mole of MgCl2= 95 grams
2.4 moles of MgCl2 = X
X= 2.4 X 95= 228 grams if MgCl2

Example 2
What’s the mass of 3.3 moles of calcium oxide (CaO)?
1 mole of Calcium oxide= Molar mass of CaO
Again, you can look up the mass of elements in the periodic table .
1 mole of CaO = 56 grams of CaO
3.3 moles of CaO= X
X= 3.3 x 56 = 184.8 grams of CaO

Example 3
What’s the mass of sodium chloride produced by reacting 4.5 moles of sodium with chlorine?
2Na + Cl2 ===2NaCl
From balanced chemica equation
2 moles of Na== 2 moles of NaCl

4.5 moles if Na== X
X= 4.5 X 2 /2
×= 4.5 moles of NaCl

Now. I need to convert the mole to mass.
Then stoichiometry conversion
Again, conversion factor remains same
1 mole of NaCl = 58.5 grams of NaCl
4.5 moles of NaCl= X
X= 4.5 X 58.5 NaCl2
X= 63.25 grams of sodium chloride.

Example 4
Calculate the mass of potassium chloride produced by reacting 4 moles of potassium!
K + NaCl == KCl + Na
Using stoichiometry calculations principle
1 mole of K ==1 mole of KCl
4 moles of K == X
X= 4 moles of KCl
Then stoichiometry conversion
1 mole of KCl ==74.5 grams
4 moles of KCl == x
X= 4 x 74.5 grams
X= 298 grams of Potassium chloride

Mole vs Volume Stoichiometry Conversions

To convert mole to volume, you only need to recall the molar volume which is however constant. I’ll need to mention that the volume of a gas at standard temperature and pressure is always 22.4 dm3 while volume at room temperature is 24 dm3.

Conversion factor
The conversion factor is
1 mole of a gaseous substance = molar volume

Example 1:

Convert 1.2 mole of chlorine gas to its volume.


To convert to volume
You need to recall the conversion factor
I mole of Cl2 == molar volume
1 mole of Cl2 == 22.4 dm3
1.2 mole of Cl2== X
X= 1.2 X 22.4
X= 26.88 dm3

Example 2:

What is the volume of 2.5 moles of ammonia gas?
1 mole of ammonia = molar volume
Hint: volume is constant for all gaseous substances
1 mole of NH3 ==22.4 dm3
2.5 mole of Nh3== ×
X= 2.5 X 22.4
X= 56 dm3

Example 3

What volume of sulphur vi oxide is evolved by reacting 3.3 moles of sulphur iv oxide
2SO2 + O2===2SO3

Again, first you calculate number of moles sulphur vi oxide

2 moles of SO2 ==2 moles of SO3
3.3 moles of SO2== X
X= 3 3 x2 /2
×= 3.3 moles if sulphur vi oxide

Then convert to volume
Recall that 1 mole of a gaseous substance is equal to molar volume
So 1 mole of SO3= 22.4 dm3
3.3 moles of SO3= X

X= 3.3 X 22.4
X= 73.92 dm3
Example 4
What volume of hydrogen gas is evolved by reacting 4.4 moles of zinc with Hydrochloric acid.
Zn + 2HCl=== ZnCl2 + H2
1 mole of Zinc == 1 mole of Hydrogen gas
4.4 moles of Zinc == X
X= 4.4 X 1 = 4 4 moles of Hydrogen gas

Then convert to volume
1 mole of gas == molar volume
1 mole of gas == 22.4 dm3
4.4 moles of gas == X
X= 4.4 X 22.4
X=985.6 dm3

Mole to number of particles stoichiometry conversion

Mole can also be related to number of particles which is Avogadro’s number ( 6.02 X 10 ^23)

Example 1

How many particles are there in 3.3 moles of sodium ?

1 mole of Na= Avogadro’s number
I mole of Na== 6.02 X 10^23
3.3 moles of Na==X
X= 3.3 X 6.02 X 10^23= 19.87 X 10 ^23

Example 2

How many atoms are there in 1.5 mole of Oxygen?
1 mole of Oxygen = Avogadro’s number

1 mole of Oxygen = 6.02 X 10^23
1.5 mole of Oxygen = X
X= 1.5 X 6.02 X 10^23
X= 9.02 X 10^23 atoms of Oxygen

So stoichiometry conversion in this case deals with the various ways parameter can be converted to other parameters

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