Question

Q7 Calculate the followings
a) Number of molecules in 90 gm of H20 and in 32 gm of S;
b) Number of atoms in 4.25 gm of NH,
c) Number of ions in 5.85 g of sodium chloride
d) Number of moles in 3.0115* 1023
e) Number of molecules in 18 L of water
f) Weight of 4 moles of CO2​

Answer 1

1. a :

• GIVEN DATA :

Given mass of H20 = 90 gm

Molar mass = 18g/mol

• TO FIND:

Number of molecules =?

• SOLUTION:

Number of molecules = Mass of substance/ Molar mass ×

Avagadro 's no.

= 90/18 × 6.02 × 10^23

= 30.1 ×10^23 of molecules

• GIVEN DATA :

Given mass of S =32gm

Molar mass =32gm/mol

• TO FIND :

Number of molecules =?

• SOLUTION :

Number of atoms = Mass of substance/ Molar mass ×

Avagadro 's no.

= 32/32 × 6.02 × 10^23

= 6.02 ×10^23

Number of molecules = 6.02x 10^23÷2

= 3.01 ×10^23 of molecules