Mole Concept and Numerical Problems

After understanding the terms like atoms and molecules, the average atomic mass of that element can be computed. Atomic Mass is a number which indicates how many times heavier is an average atom of that element as compared with 1/12 of the mass of an atom of C-12. Atomic mass unit or Unified unit (amu or u) is a mass exactly equal to one-twelfth the mass of one C-12 atom. Molecular Mass is the sum of atomic masses of the elements present in a molecule Molar mass is the mass of one mole of a substance in grams.

Atoms and molecules are extremely small in size and their numbers in even a small amount of any substance is really very large. To handle such large numbers, a unit of similar magnitude is required. In SI system, mole was introduced as seventh base quantity for the amount of a substance. One mole is the amount of a substance that contains as many particles or entities as there are atoms in exactly 12 g of carbon-12 isotope. One mole of a substance always consists of 6.022x1023 particles. The number of particles in one mole of a substance (element or compound) is known as the Avogadro’s number. It is equal to 6.023 x 1023. It can be determined by Millikan oil drop experiment and radioactive measurements. There are various applications of mole concept such as in calculating absolute weight of an atom or a molecule.

Victor Meyer is best known for inventing an apparatus for determining the molecular mass of a volatile substance. This apparatus is known as the Victor Meyer apparatus.

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