Notes On Mole Concept And Percentage Composition - CBSE Class 11 Chemistry
Mole is the amount of substance, which contains as many elementary entities as there are in 12 gram of carbon. Elementary entities  may be atoms, molecules, ions, electrons or protons. 1mole of a substance always contains the same number of entities irrespective of the identity and kind of the substance. 1mole of any atom/molecule always contains ‘6.022 x 1023’number of atoms/molecules. Ex: 1mole of water (H2O) contains 6.022 x 1023’number of water molecules Avogadro’s number or Avogadro’s constant is the number of elementary entities (atoms or molecules) in 1mole of a substance. Molar mass is the mass of 1mole of substance in grams. Molecular mass of a substance can be obtained by adding the atomic masses of all the atoms present in one molecule of the substance. The molar mass is numerically equivalent to the atomic (or molecular or formula) mass in u. Molar mass and percentage composition can be useful to understand the quantitative data associated with a chemical compound. The percentage of any element or constituent is, Percentage of an element or constituent = No. of parts by mass of the element or constituent / Molar mass of the compound x 100 The chemical formula of a compound is derived from two parts. They are,                      → Empirical Formula                    → Molecular Formula The empirical formula gives the simplest whole number ratio of the different atoms present in one molecule of the compound. The empirical formula mass is the sum of the atomic masses of the atoms present in the element. The molecular formula gives the actual number of atoms of various elements present in one molecule of a compound. It is an integer multiple of the empirical formula.

#### Summary

Mole is the amount of substance, which contains as many elementary entities as there are in 12 gram of carbon. Elementary entities  may be atoms, molecules, ions, electrons or protons. 1mole of a substance always contains the same number of entities irrespective of the identity and kind of the substance. 1mole of any atom/molecule always contains ‘6.022 x 1023’number of atoms/molecules. Ex: 1mole of water (H2O) contains 6.022 x 1023’number of water molecules Avogadro’s number or Avogadro’s constant is the number of elementary entities (atoms or molecules) in 1mole of a substance. Molar mass is the mass of 1mole of substance in grams. Molecular mass of a substance can be obtained by adding the atomic masses of all the atoms present in one molecule of the substance. The molar mass is numerically equivalent to the atomic (or molecular or formula) mass in u. Molar mass and percentage composition can be useful to understand the quantitative data associated with a chemical compound. The percentage of any element or constituent is, Percentage of an element or constituent = No. of parts by mass of the element or constituent / Molar mass of the compound x 100 The chemical formula of a compound is derived from two parts. They are,                      → Empirical Formula                    → Molecular Formula The empirical formula gives the simplest whole number ratio of the different atoms present in one molecule of the compound. The empirical formula mass is the sum of the atomic masses of the atoms present in the element. The molecular formula gives the actual number of atoms of various elements present in one molecule of a compound. It is an integer multiple of the empirical formula.

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