Chapter 3: Atoms and Molecules

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Q
Atoms and Molecules

Question:

Q.8: Convert into mole.

(a) 12 g of oxygen gas

(b) 20 g of water

(c) 22 g of carbon dioxide

Answer:

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

mathbf{{color{Magenta} Number of moles =(frac { Given mass }{ Molar mass })}}

 

(a) The given mass of oxygen gas is 12g. The molecular formula of oxygen gas is O2. The gram atomic mass of oxygen is 16g. 

Molar mass of oxygen gas = 2(atomic mass of O) = 2(16g) = 32g

mathbf{{color{DarkBlue} oldsymbol{mathbf{}}Number of moles  =frac { 12}{ 32 } =0.375 mol}}

Therefore, the correct answer is 0.375 mol.

 

(b) The given mass of water is 20g. The molecular formula of water is H2O. The gram atomic mass of oxygen is 16g and hydrogen is 1g 

Molar mass of water = 2(atomic mass of H) + (atomic mass of O) = 2(1g) + 16g = 18g

mathbf{{color{DarkBlue} oldsymbol{mathbf{}}Number of moles  =frac { 20}{ 18 } =1.111 mol}}

Therefore, the correct answer is 1.111 mol.

 

(c) The given mass of carbon dioxide gas is 22g. The molecular formula of water is CO2. The gram atomic mass of oxygen is 16g and carbon is 12g 

 Molar mass of carbon dioxide gas = (atomic mass of C) + 2(atomic mass of O) = 12g + 2(16g) = 44g

mathbf{{color{DarkBlue} oldsymbol{mathbf{}}Number of moles  =frac { 22}{ 44 } =0.5 mol}}

Therefore, the correct answer is 0.5 mol.


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