Welcome to Chem Zipper.com......: Principle of atom conservation (PAOC):

## Tuesday, April 2, 2019

### Principle of atom conservation (PAOC):

We know that, in a chemical reaction, the atoms of each element remain conserved. If atoms are conserved, moles of atoms will also be conserved. This is known as the principle of atom conservation.

Total number of moles of an atoms of an element on reactant side = Total number of moles of atoms of an on product side.

Illustration of POAC: Take a chemical reaction as example.

(A) According to the principle of atom conservation (POAC) for K atoms:

Total moles of K atoms in reactant = total mole of K atoms in products

or

Moles of K atoms in KClO3 = moles of K atoms in KCl.

Now, since 1 molecule of KClO3 contains 1 atom of K, 1mole of KClO3 contains 1 mole of K similarly, 1mole of KCl contains 1mole of K.

Thus, mole of K atoms in KClO= 1 × moles of KClO3

And mole of K atoms in KCl = 1 × moles of KCl

Hence            1 × moles of KClO3 = 1 × moles of KCl

(B) Similarly applying the principle of atom conservation for O atoms:

Mole of O in KClO3 = 3 ×moles of KClO3

And moles of O in O2 = 2 × moles of O2

3 × moles of KClO3 = 2 × moles of O2

Illustrative example (1): Write the POAC equations for all the atoms in the following reaction.

Illustrative solution:

Applying POAC on (P) atoms:

P à H3PO4

Numbers of moles of (P) atoms in P4 = Numbers of moles of (P) atoms in H3PO4

4x nP4= 1x nH3PO4

Applying POAC on (H) atoms:

1x nHNO3 = 3 x nH3PO4 + 2 x nH2O

Applying POAC on (N) atoms:

1 x nHNO3 = 1 x nNO2

Applying POAC on (O) atoms:

3 x nHNO3 = 4 x nH3PO4 +2 x nNO2 + 1nH2O

Related Questions:

### Illustrative example (6) In a determination of P an aqueous solution of NaH2PO4 is treated with a mixture of Ammonium and magnesium ions to precipitate magnesium Ammonium phosphate (Mg(NH4)PO4.6H2O. This is heated and decomposed to magnesium pyrophosphate. Which is weighed. A solution of NaH2PO4 yield 3.33 gm of Mg2P2O7. What is weighed of NaH2PO4 was present originally.

1. 2. 