CBSE Class 9 Answered

Here is a graphic of the procedure steps:

Problem #1: 0.200 mole of H₂O contains how many molecules?

Solution:   no.of moles =given no of particles/Avogadro no.

given no of particles =  no.of moles x Avogadro no.

0.200 mol x 6.022 x 10²³ mol¯¹

2. moles = mass ÷ molar mass

Calculate the moles in 124.5 g of oxygen gas.

1. Write the equation: 
   n = m ÷ M

    

2. Extract the data from the question: 
   m = 124.5 g

    

3. Calculate the molar mass of the substance using the periodic table: 
   M(O₂) = 2 x 16.00 =32.00 g mol^-1

    

4. Substitute the values into the equation and solve: 
   n = 124.5 ÷ 32.00 = 3.89 mol