Mass to Molecule

A mass to molecule probelm is one in which the mass of a reactant or product is given. You are then asked to calculate the the number of molecules of another reactant required or the mass of another product formed.


Example 1:

Iron is prepared by reacting iron ore (Fe₂O₃) with carbon monoxide (CO). Iron and carbon dioxide result from the reaction. How many molecules of CO would react with 600 g of iron ore?

Step 1

Write the balanced equation, mole ratio, and masses beneath the required substances.

Fe2O3	+	3 CO	------>	2 Fe	+	3 CO2
1 mole		3 moles
159.6 g		3(6.02x1023)molecules

Step 2

Write the given and the unknown beneath the appropriate substance.

Fe2O3	+	3 CO	------>	2 Fe	+	3 CO2
1 mole		3 moles
159.6 g		3(6.02x1023)molecules
600g		X molecules

Step 3

Set up a ratio:

159.6 g	=	3(6.02x1023)molecules
600 g		X molecules

Step 4

Solve for "X". Use cross multiplication.

159.6 g x X g = 600 g x 3(6.02x10²³)molecules

X =6.79 x 10²³ molecules

Therefore 6.79 x 10²³ molecules of carbon monoxide will react with 600g of iron ore.

 

Example 2: Example 2: You fill in the missing parts!

We'll use the same reaction as above, but this time caculate the number of molecules of carbon dioxide formed if 300 g of iron was produced.

Solution:

Step 1

Write the balanced equation, mole ratio, and molar masses and molecules beneath the required substances.

Fe2O3	+	3 CO	------>	2 Fe	+	3 CO2
				2 mol		3 mol
				2(112)		3(6x10 23)

Step 2

Write the given and the unknown beneath the appropriate substance.

          
 Fe2O3

          
+

          
 3 CO

          
 ------>
 
          2 Fe

          
 +

          
 3 CO2
 
 
 
 
          
          
          300 g
          
 
 
          
          
          X molecules
          
Step 3

Set up a ratio:

2(112)g	=	3(6x10 23)
300 g		X molecules

Step 4

Therefore X = 2.4 x 10 to the 24 molecules

Therefore if 300 grams of iron was produced 2.4 x 10 to the 24 molecules molecules of carbon dioxide were produced .

 

For some extra problems click here.

For some more problems click here.

Next page of tutorial (Volume to Volume Stoichiometry)

 

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