Mole Concept and Mole Conversions

We have a score of items meaning 20. Then there is the dozen to mean 12 items. The mole identifies a very large number of items. The mole is a unit that is defined as 6.023 X 1023 particles. It is also equal to the formula mass of a substance expressed in grams. For example:

1 mole of H2O = 6.023 X 1023 molecules of H2O = 18 grams H2O

This statement establishes the relationship between mole units and molecule units and the relationship between mole units and gram units.

The following are examples as to how the mole concept is applied:

  1. Mole To Gram Conversion
  2. Mole to Molecules Conversion
  3. Mole to Atom Conversion
  4. Practice Problem

Mole to gram conversion

Determine the number of grams in 4 moles of H2O

Formula mass H2O = (2 x 1.0) + (1 x 16) = 18

1 mole H2O = formula mass H2O = 18 grams H2O

4 moles H2O x 18 grams / 1 mole = 72 grams H2O

Gram to Mole conversion

Determine the number of moles in 88 grams of CO2

Formula Mass CO2 = (1 x 12) + (2 x 16) = 44

1 mole of CO2 = formula mass CO2 = 44 grams CO2

88 grams CO2 x 1 mole CO2 / 44 grams CO2 = 2 moles CO2

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Mole to molecule conversion

Determine the number of molecules of H2O in 3 moles H2O

1 mole H2O = 6.023 X 1023 molecules H2O

3 moles H2O x 6.023 X 1023 molecules H2O / 1 mole H2O = 18.069 X 1023 molecules H2O = 1.8069 X 1024 molecules H2O

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Mole to Atoms Conversion

How many atoms are present in 17.0 mol of water?

In order to convert mols of a substance to atoms one must first convert mols to molecules

step 1. mols ----> molecules

The relationship between mols and molecules is:

1 mol of any substance = 6.023 X 1023 molecules of that substance.

17.0 moles H2O X 6.023 X 1023 / 1 mole H2O = 102.4 X 1023 = 1.02 X 1025 molecules H2O

step 2. molecules of substance ----> total atoms

That would depend upon the formula of the substance which in this case is H2O

The subscripts that appear right after the symbol representing an element can be interpreted as atoms of that element in one molecule of the substance.

According to the formula for H2O:

1 molecule H2O = 2 atoms H + 1 atom O = 3 atoms total

So once you have determined the number of molecules of H2O from step 1 you then can use the above relationship between molecules and total atoms to determine the total atoms in the number of molecules determined in step 1

1.02 X 1023 molecules H2O X 3 atoms / 1 molecule H2O = 3.06 X 1023 atoms total

Here is a problem for you to try out:

Given 5 moles of Sulfuric Acid having a formula of H2SO4 answer the following questions:

  1. How many grams of Sulfuric Acid would this be?
  2. How many molecules of Sulfuric Acid would that be?
  3. How many Hydrogen atoms would be in this amount of Sulfuric Acid?
  4. How many Oxygen atoms would there be in this much Sulfuric Acid?

When you have finished working all four parts, you may check your results with the correct solutions

You may find other useful problems involving mole concept and conversion at the following sites. To return to this site from the below sites just click on the BACK button or the LEFT ARROW on your browser.

  1. mole conversion problems (problem sets developed by S.E. Van Bramer for chemistry and environmental science courses at Widener University.)

  2. The ChemTeam's Mole Problems

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R. H. Logan, Instructor of Chemistry, Dallas County Community College District, North Lake College.

Send Comments to R.H. Logan: AACProfchm@aol.com 

All contents copyrighted (c) 1996
R.H. Logan, Instructor of Chemistry,DCCCD
All Rights reserved


Revised: 10/2/98


Original Date of Creation: 11/16/96








Solution to the Problem



Given 5 moles of Sulfuric Acid having a formula of H2SO4 answer the following questions:

    

  1. How many grams of Sulfuric Acid would this be?

    
Formula Mass H2SO4 = 2(1.0)+ 1(32)+ 4(16) = 98

    
1 mole H2SO4 = Formula Mass H2SO4 in grams = 98 grams H2SO4

    
5 moles H2SO4 X 98 grams / 1 mole = 490 grams

    

  2. How many molecules of Sulfuric Acid would that be?

    
1 mole H2SO4 = 6.023 X 1023 molecules H2SO4

    
5 moles H2SO4 X 6.023 X 1023 molecules / 1 mole = 30.1 X 1023 = 3.01 X 1024 molecules H2SO4

    

  3. How many Hydrogen atoms would be in this amount of Sulfuric Acid?

    
In H2SO4 there is:

    
2 atoms H = 1 molecule H2SO4

    
3.01 X 1024 molecules H2SO4 X 2 atoms H / 1 molecule H2SO4 = 6.02 X 1024 atoms H

    

  4. How many Oxygen atoms would there be in this much Sulfuric Acid?

    
In H2SO4 there is:

    
4 atoms O = 1 molecule H2SO4

    
3.01 X 1024 molecules H2SO4 X 4 atoms O / 1 molecule H2SO4 = 12.04 X 1024 = 1.204 X 1025 atoms O


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