Mole Concept, Molar Mass And Percentage Composition

We all want to know that in a particular substance how many molecules are present. Molecules and atoms are very tiny, both in size and mass.

What is a Mole?

In a substance, the amount of entities present for e.g. atoms, molecules, ions, is defined as a mole. A mole of any substance is \(6.022×10^{23}\) molecules. Just as we take a standard value to calculate different things e.g. 1 dozen =12 items similarly we use the mole to calculate the size of the smallest entities quantitatively.

Mole Concept

The amount of atoms present in 12g (0.012 kg) of the \({12}^C\) isotope is the amount of particles present in 1 mole of the substance. One of the most important facts that should be kept in mind is that the mole of a substance always contains the same number of entities whatever the substance may be.

To know the number precisely the mass of carbon-12 atom was calculated by using a mass spectrometer and it was found to be \(1.992648×10^{-3}g\).

As we know that one mole of carbon weighs 12g, the total no. of atoms in it is equal to \(6.0221367×10^{23}\). The no. of entities in 1 mole plays a vital role in calculations in chemistry. That is why it is given a name called Avogadro’s number(NA). From the above discussion, we can say that the number of atoms present in 1 mole of hydrogen is equal to \(6.022×10^{23}\).

What is molar mass?

A substance is something which has mass and occupies space. The molar mass/molecular weight is actually the sum of the total mass in grams of the atoms present to make up a molecule per mole. The unit of molar mass is grams/mole.

What is percentage composition?

We can find the percentage composition of a substance by dividing the mass of that substance to the total mass of the substance. Suppose we have to find out the percentage composition of hydrogen in butane(\(C_4H_{10}\)) then it will be:

Total mass of one mole of butane =58.123

Mass of hydrogen in one mole of butane = 10.0794

Therefore, mass percent of hydrogen in butane=\( \frac{10.079}{58.123}×100\)=\(17.3 %\)

These concepts play a very important role for studying the behaviour of matter under different conditions. Know more about mole concept and the related topics, for any further help contact the mentors at Byju’s.


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