Chapter 3: Atoms and Molecules

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Q
Atoms and Molecules

Question:

Q.9: What is the mass of:

(a) 0.2 mole of oxygen atoms?

(b) 0.5 mole of water molecules?

Answer:

The number of moles of a substance is calculated by the formula given below:

mathbf{{color{Magenta} Number of moles =left ( frac{Given mass}{Atomic mass or Molar mass} 
ight )

 

(a)  The atomic mass of oxygen is 16 g/mol. So, the mass of 0.2 moles of oxygen atoms is calculated as shown below:

mathbf{0.2 mol = frac{Mass}{16g/mol}}

mathbf{Mass = 16	imes 0.2 = 3.2g}

 

Therefore, the correct answer is 3.2g.

 

(b)  The molar mass of water is 18 g/mol. So, the mass of 0.5 moles of water molecules is calculated as shown below:

mathbf{0.5 mol = frac{Mass}{18g/mol}}

mathbf{Mass = 18	imes 0.5 = 9g}

 

Therefore, the correct answer is 9g.

 


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