Concept of Mole

  Concept of Mole:

Atomic mass,molecular mass,formula mass or ionic mass of the substance expressed in grams is called mole.

Introduction: As atoms, ions or molecular are so small particles that's why it is not easy to find the weight of one atom, one ion or one molecule. That's why we use the atomic mass unit(amu) to express the mass of these particles.

Different measuring units:There are different unit to measure the masses.

1.Gram Atom:

Atomic mass of an element expressed in grams is called one gram atom. It is also called one gram mole or simply a mole of that element.

For example:1 gram atom of hydrogen=1.008g

                       1 gram atom of carbon=12.000g

                       1 gram atom of uranium=238.0g

It means that one gram atoms of different elements have different masses.One mole of carbon is 12g,while 1 mole of magnesium is 24g.It also shows that one atom of magnesium is twice as heavy as an atom of carbon.

2.Gram Molecule:

The molecular mass of a substance expressed in grams is called gram molecule or gram mole or simply the mole of a substance.

Number of gram molecule or       =Mass in grams

moles of a molecular substance      Molar mass of the substance

For example:1 gram molecule of water=18.0g

                       1 gram molecule of H2SO4=98.0g

It means that the one gram molecules of different molecular substances have different masses.

3.Gram Molecule:

The formula mass of an ionic compound expressed in grams is called formula of the substance.

Number of gram formulas or           =Mass in grams

moles of a substance                          Formula mass of the substance

For example:1 gram formula of NaCl=58.5g

                       1 gram formula of Na2CO3=106g

4.Gram Ion:

The ionic mass of an ion expressed in grams is called gram ion or one mole of ions.

Numbers of gram ion or         =Mass of ions in grams

moles of an ion                          ionic mass of an ion

moles of an ion