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Molecular Mass :
It is the sum of the atomic masses of all atoms in a molecule of the substance.
The formula unit mass is the sum of the atomic masses of all atoms in a formula unit of a compound. It is used for those substances whose constituent particles are ions.
Na Cl - 1 x 23 + 1 x 35.5 = 58.5 μ
Mole Concept :
The word mole was introduced by Wilhelm Ostwald around 1896 and it means heap or pile.
Mole is that quantity in number having a mass equal to its atomic or molecular mass in grams. The number of particles present in 1 mole of any substance is fixed, with a value of 6.022 x 1023. This is called the Avocado Constant or Avocado Number (represented by No)1 mole = 6.022 x 1023 in number
Mass of one mole is also fixed. It is equal to its relative atomic or molecular mass in grams.
Molar mass of atoms is also known as grain atomic mass. For this ‘μ’ is changed to ‘g’.
Eg. Atomic mass of hydrogen is 1μ and its gram atomic mass is 1g.
Chemists need the no. of atoms and molecules while carrying out reactions so, they need mass in grams to the number. Thus, a mole is the chemist’s counting unit.
