Number of moles calculator

MOLE CONCEPT

Chemical reactions occur between large number of particles, and these particles may be in the form of atoms, molecules or ions and each of these particles has their own relative mass, but there is no fit in between the amounts of each matter and its mass.

For example, if a student was asked to compare 1 g of H2 gas and 1 g of N₂ gas and 1 g of O₂ gas in terms of the number of particles it cannot solved for the simple reason that the molecular masses of these elements vary from each other, the molecular mass of hydrogen gas 2, nitrogen 28 and for oxygen 32. If the mass of 1 g is divide for each item on the molecular mass.

Then values obtained can be used for comparison. So, years ago, the need arose for independent units to express the amount of substance and this unit had found general acceptance, this unit is mole (mole) and symbolizes (n) and it is one of the basic units in the international system of units, the mole defined as the quantity of material containing the same number of particles (molecules, atoms or ions) containing in 12 g of carbon isotope 12 (12C) (where this isotope is used also as a measure to calculate atomic mass as previously mentioned) and this number of particles called the Avogadro's Number) which equals to 6.023 × 10*²³ and symbolizes N_A. It must be emphasized that Mole is the actual amount of the matter and is not the mass.

The Mole is one of the most important basic concepts in general chemistry and which adopted by scientists to consolidate their theory to many important is- sues in chemistry. And we can apply the concept of mole on atoms, molecules, ions or electrons so it is always necessary to specify the type of particle that we deal with, for example,

·       Mass of one mole of atoms of the isotope carbon-12 is 12 g

·       Mass of one mole of atoms of silver is 107.868 g

·      Mass of one mole of H₂ molecules are 2 g

·       Mass of one mole of ions SO4*^2- is 96 g

And number of moles (n) is calculated using the following relationship:

n (mol) = mass (m) (g) / molar mass (M) (g/mol)

Applications of Mole Concept

As we have told before, the mass of 1 mole of carbon atom is 12 grams. According to this, it is possible to calculate the mass of 1 carbon atom.

We can write the following equation:

Number of moles = Number of particles (atoms, ions or molecules)/ Avogadro's number

Example 1

a. Calculate the number of moles of 3.01×10*²⁵ water molecules.

b. Calculate the number of molecules in 0.02 mole of CO₂.

Solution:

Example 2

Calculate the number of molecules in 170 g of H2S gas.

Solution:

Exercises

1.      What is the number of moles in 5.6 g of PCl5?

2.     Calculate the number of molecules of SiO2 found in 1mg of dust. (Assume that dust particles are made up of 100% SiO2.)