Page 18 - 11-chem-1

1.BASIC CONCEPTS eLearn.Punjab

Number of gram molecules or moles of a molecular substance = Mass of molecular substance in grams
Molar mass of the substance

For example

and 1 gram molecule of water = 18.0 g

1 gram molecule of H2SO4 = 98.0 g
1 gram molecule of sucrose = 342.0 g

It means that one gram molecules of different molecular substances have different masses.
The formula unit mass of an ionic compound expressed in grams is called gram formula of
the substance. Since ionic compounds do not exist in molecular form therefore the sum of atomic
masses of individual ions gives the formula mass. The gram formula is also referred to as gram
mole or simply a mole.

Number of gram formulas or moles of a substance = Mass of the ionic substance in grams
Formula mass of the ionic substance

1 gram formula of NaCl = 58.50 g

1 gram formula of Na2CO3 = 106 g
1gram formula of AgNO3 = 170g
Itmayalsobementionedherethationicmassofanionicspeciesexpressedingramsiscalledonegramionor

one mole of ions.

Number of gram ions or moles of an species = Mass of the ionic species in grams
Formula mass of the ionic species

For example

1 g ion of OH- = 17g

1 g ion of SO42-=96g
1 g ion of CO32- =60g
So, the atomic mass, molecular mass, formula mass or ionic mass of the substance expressed

in gram is called molar mass of the substance.

18