Molar Calculations with Examples

Molar Calculations with Examples

Mass and Mole Relation:

1 mole N atom contains 14,01 g N

Mass of NO2 is;

14,01+2.(16,00)=46,01 amu  Thus;

1 mole NO2 is 46,01g  NO2

1 mole N2 molecule is 2x14,01=28,02 g N2

Atom-gram, molecule-gram:

1 atom- gram Ca=1 mole Ca

1 molecule-gram CO2=1 mole CO2

Example: Which one of the following statements are true for compound P2O5 including 12,4 g P.(P=31)

I. 0,2 molecule-g

II. Contains 6,02x1023 O atom

III. Contains 1,4 mole atom


1 mole P atom is 31 g

X mole P atom is 12,4 g


X=0,4 mole P atom

I. 1 mole P2O5 contains 2 mole P atom

X mole P2O5 contains 0,4 mole P atom


X=0,2 mole P2O5

Thus, 0,2 mole P2O5 is 0,2 molecule-gram

II. 1 mole P2O5contains 5 N O atom

0,2 mole P2O5 contains X N O atom


X= NO atom where N=Avogadro’s number

III. 1 mole P2O5 contains 7 mole atom

0,2 mole P2O5 contains X mole atom


X=1,4 mole atom

Be Careful!

Atomic mass and mass of one atom is always confused. Atomic mass is the mass of one mole element in terms of gram. On the other hand, mass of one atom is used for in real meaning, it is equal to mass of one atom in an element and it is too small. In the same way, molecule mass and mass of one molecule is confused, be careful in using these terms.

Atomic Mass Unit, Gram Relation

1  O atom 16 amu

1 O atom 16/N g

where N is Avogadro’s number

Volume of Gases Mole Relation

Under same conditions ( temperature and pressure) gases contains same number of atoms and under same conditions mole and volume of gases are directly proportional to each other.

1 mole gas is 22,4 liter under standard conditions.

Example: Following compounds contain same number of H atoms. Find relation between their volumes.

I. CH4

II. C2H2


Solution: Under standard conditions gases have equal number of atoms or molecules.

we should take equal mole of H from each compound thus;

3 mole CH4

6 mole C2H2

2 mole C3H6

mole and volume are directly proportional to each other

II>I>III is the relation of volumes and moles of compounds given above.

Example: Find the relation between number of atoms of given compounds below.

I. Under normal conditions, 4,48 liter He gas

II. 3,01x1022 SO3 molecule

III. 1,6 g O2 molecule



1 mole He is 22,4 liter

X mole He    4,48 liter


x=0,2 mole He

0,2 mole He contains 0,2 mole He atom


1 mole SO3 contains 6,02x1023 SO3 molecule

X mole SO3 contains 3,01x1022 SO3 molecule


X=0,05 mole SO3

in 1 mole SO3 there are 4 mole atom

0,05 mole SO3 there are X mole atom


X=0,2 mole atom

III. 1 mole O atom is 16 g

X mole O atom is 1,6 g


X=0,1 mole

Relation between them becomes;


The Mole Concept Exams and Problem Solutions