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| 1. |
molecular mass and mole concept |
| Answer» The molecular mass of a substance is the sum of the atomic masses of all the atoms in a molecule of the substance.\xa0It is expressed in atomic mass unit (u).Mole Concept:We know that a dozen is a collect ion of 12 substances, a century is a collection of 100 substances and a gross is a collection of 144 substances. We use the terms dozen, century, gross etc. to express a certain quantity of a substance. Similarly, a mole is a word used to describe a collection of particles i.e. atoms, molecules or ions.1 mole of a substance is equal to its atomic mass or molecular mass expressed in grams. The atomic mass expressed in grams is the gram atomic mass. The molecular mass expressed in grams is the gram molecular mass.For example, The atomic mass of sodium is 23 grams.Therefore, 23 grams of sodium is equal to one mole of sodium atoms.Similarly, the molecular mass of oxygen (O2) = 2 × Atomic mass of oxygen= 2 × 16 = 32 gAvogadro experimentally found that one mole of any substance always contained 6.022 × 1023 particles.This number is called the Avogadro’s number, denoted by N0. | |