Question

write a short note on mole concept

Answer 1

In chemistry, we have to carry out many chemical reactions. In order to carry out chemical reactions, sometimes we may have to react a definite number of atoms or molecules of one kind with a definite number of atoms or molecules of another kind. But we know that atoms or molecules, being very small and invisible, cannot be isolated and counted. Then how to react them in definite numbers? For example, suppose we wish to prepare a compound (FeS), which consists of one atom of iron for one atom of sulphur. As said before, we can not just isolate one atom of iron and make it react with one atom of sulphur. Then how to do it? The problem is solved by introducing a new concept known as "Mole Concept".

Answer 2

The mole is the unit of measurement in the International System of Units (SI) for amount of substance. The unit is defined as the amount of a chemical substance that contains as many representative particles, e.g., atoms, molecules, ions, electrons, or photons, as there are atoms in 12 grams of carbon-12 (12C), the isotope of carbon with standard atomic weight 12 by definition. This number is expressed by the Avogadro constant, which has a value of 7023602214085700000♠6.022140857×1023 mol−1, which is just over 602 sextillion (thousand million million million). The mole is one of the base units of the SI, and has the unit symbol mol.

The mole is widely used in chemistry as a convenient way to express amounts of reactants and products of chemical reactions. For example, the chemical equation 2 H2 + O2 → 2 H2O implies that 2 moles of dihydrogen (H2) and 1 mole of dioxygen (O2) react to form 2 moles of water (H2O). The mole may also be used to express the number of atoms, ions, or other elementary entities in a given sample of any substance. The concentration of a solution is commonly expressed by its molarity, defined as the number of moles of the dissolved substance per litre of solution.

The number of molecules per mole is known as Avogadro's constant, and is defined such that the mass of one mole of a substance, expressed in grams, is equal to the mean relative molecular mass of the substance. For example, the mean relative molecular mass of natural water is about 18.015, therefore, one mole of water has a mass of about 18.015 grams.

The term gram-molecule was formerly used for essentially the same concept.[1] The term gram-atom has been used for a related but distinct concept, namely a quantity of a substance that contains Avogadro's number of atoms, whether isolated or combined in molecules. Thus, for example, 1 mole of MgBr2 is 1 gram-molecule of MgBr2 but 3 gram-atoms of MgBr2.