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1.BASIC CONCEPTS eLearn.Punjab

Solution:

Mass of ice (water) = 10.0 g
Molar mass of water =18gmol-1

Number of molecules of water = Mass of water in gram x Avogadro's number
Molar mass of water in g mol−1

= 10 x 6.02 x 1023
18 g mol-1

Number of molecules of water = 0.55 x 6.02 x 1023 = 3.31 x 1023 Answer
One molecule of water contain hydrogen atoms = 2
3.31 x 1023 molecules of water contain hydrogen atoms = 2 x 3.31 x 1023

One molecule of water contains oxygen atom = 6.68 x 1023 Answer
=1

3.31 x 1023 molecules of water contain oxygen atoms = 3.31 x 1023 Answer

One molecule of water contains number of covalent bonds =2

3.31 x 1023 molecules of water contain number of covalent bonds = 2 x 3.31 x 1023

Total number of atoms of hydrogen and oxygen = 6.68 x 1023 Answer
= 6.68 x 1023 + 3.31 x 1023

= 9.99 x 1023 Answer

Example (9):

10.0 g of H3PO4 has been dissolved in excess of water to dissociate it completely into ions.
Calculate,

a) Number of molecules in 10.0 g of H3PO4.
b) Number of positive and negative ions in case of complete dissociation in water.

c) Masses of individual ions.

d) Number of positive and negative charges dispersed in the solution.

Solution:

(a) Mass of H3PO4 =10 g

Molar mass of H3PO4 =3 + 31 + 64 = 98

No. of molecules of H3P04 = Mass of H3PO4 x 6.02 x 1023

= Molar mass of H3PO4

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