Learn about grams to moles & moles fraction

by James Johnson Teacher / Writer

What is a Mole?

Mole is universally recognized as a standard unit of measurement in Chemistry. Putting it in a more comfortable way, any substance consisting of its underlying ingredients will be referred to as 1 mole if it has the same number of particles present in the 12 gram Carbon atom. 

There are 6.022 * 1023 particles found in the 12 grams of the Carbon atom; hence one mole is equal to the 6.022 * 1023 particles of Carbon. It is hereby pertinent to mention that you should not measure this unit with respect to the isotopes of Carbon; this should be C-12.

In practice, it is convenient to write 1 mole instead of penning the numerical value of Avogadro's number. NA or L usually denotes this Avogadro's constant.

Why do we use a Mole instead of Gram?

The answer to the question that "Why do we use moles in Chemistry" lies in the heart of its evolution and historical background. Needless to say and point out how tiniest an atom could be, but just to provide you the insight, always remember that Greek philosopher and naturalist Democritus addressed it with the Greek word "Atomos" which means a particle that cannot be divided anymore. Hence, the other standard version of measuring stuff like Kg, and Gram would not be sufficient enough to estimate the particles dwelling in the 12g of a Carbon atom. 

By incorporating a new unit and assigning it to the value of Avogadro's number makes it easier to determine the proportional ratio of chemical substances in any synthetically or naturally existing solution. There are many other reasons to praise this effort of devising a mole as a unit of measuring the particles in atoms. The Avogadro's number bridged the Theoretical Chemistry with Atomic Physics; it opened many avenues and unraveled dozens of secrets inside the molecule.


Gram to Mole Conversion

Formally saying, there is no generic formula for converting Gram to the mole. You only need to have the value of atomic masses of elements involved in under considering reaction (having a periodic table in the pocket will get you out), and the formula mass value of atoms.

Let's suppose we have 400 grams of carbon dioxide gas CO2, and we need to find the number of moles in it. At the start, we just need to trace the atomic masses of each element of our problem statement in a periodic table.

After consulting the periodic table, I came across that the atomic mass of Carbon is 12.01, and oxygen is 16.00 g. Now, as CO2 involves two atoms of oxygen with one atom of Carbon, hence the formula mass will be,


      1 mol CO2   = 12 + 2(16) = 44g

This shows 1 mole of CO2 carries 44g of particles, so conversely, 1 gram of CO2 will carry (1/44) moles. 


       44g CO2    = 1 mol CO2

1g CO2      = 1 mol CO2


      400g  CO2 = 1 mol * 400g 


Thus, 400 grams of CO2 will contain 9.0 moles of CO2. There are online grams to moles calculators which provide accurate results and use the same formulas.      

What is Mole Fraction?


Mole discusses the amount of a molecule in a chemical element, whereas Mole fraction deals with the concentration of a specific substance in any mixture. It is always tricky and cumbersome to determine the amount of substance in a solution of liquid or gas. Mole fraction is the fraction or ratio of one mole of substance to the total number of all substances. 

Formula and its Example  

For a mixture of two, three or N numbers of substances the mole fraction of each substance would be written as follow, 


XA =       mol A      ,…….,    XN = ____mol N_______

         mol A+ mol B               mol A +... mol N

If we have a solution of 5.5 g of alcohol in 40 g of H2O, where the mass of H2O is 18, and the mass of CH3OH is 32.

If we need to determine the mole fraction of CH3OH in this dissolved solution. For this, we will find the moles of both required substances, i.e., 

Moles of CH3OH = 5.5 / 32 = 0.17 mole

Moles of H2O = 40 / 18 = 2.2 moles


Now, in order to find the mole fraction, we will have 

Mole fraction of CH3OH = 0.17

              (2.2 + 0.17)

Mole fraction of CH3OH = 0.071 

You can also use a mole fraction calculator to solve this quickly without spending too much time doing manual calculations. 

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About James Johnson Freshman   Teacher / Writer

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Joined APSense since, January 8th, 2020, From Birmingham, Al, USA, United States.

Created on May 21st 2020 02:25. Viewed 493 times.


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