9th chemistry Self-evaluation on Mole concept

Sample Problem 1. Calculate the number of mole in 52 g of Helium.

Solution. We know that, Atomic mass of He = 4u

So, its molar mass = 4 g  That is, 4 g of He contains 1 mole of He.

Or, 4 g of He = 1 mole of He

Or, 1 g of He = 1/4 mole of He

So, 52 grams of Helium =1/4 x 52 mole = 13 moles

Therefore, there are 13 moles in 52 g of He

Sample Problem 2. Calculate the number of moles for 12.044 X 10²³ atoms of Helium.

Solution: 

6.022 X 10²³ atoms of Helium           = 1 mole

1 atom of Helium                                 =1/6.022 X 10²³ mole

12.044 X 10²³ atoms of Helium         = [(1/6.022 X 10²³) x  12.044 X 10²³  ]moles

[ You may use  ----        Number of moles    = (given numbers of particles /Avogadro number)]

Sample Problem 3. How many moles are there in 5 grams of calcium?

Sample Problem 4. How many moles there in 12.044 X 10²³ atoms of phosphorous?

Sample Problem 5. Calculate the mass of 0.5 mole of Nitrogen atoms.

Solution. We know that, Molar mass of of Nitrogen atoms 14 g

The mass of 1 mole of Nitrogen atoms = 14 g

The mass of 0.5 mole of Nitrogen atoms = 14x 0.5 g = 7 g

Alternate method,

                        Mass = Number of moles X Molar mass

                  Or,           = 0.5 X 14 = 7 g

Therefore, mass of 0.5 mole of N atoms is 7 grams.

Sample Problem 6. What is the mass of 3.011 X 10²³ number of Nitrogen atoms?

Solution. We know that, Molar mass of of Nitrogen atoms 14 g

The mass of   6.022 X 10²³ number of Nitrogen atoms= 14 g

The mass of  3.011 X 10²³ number of Nitrogen atoms = [(14g/6.022 X 10²³ )x 3.011 X 10²³]g = 7 g

Sample Problems 
Sample Problem 7. Calculate the number of particles in each of the following:

(i) 0.1 mole of Carbon atoms  (ii) 46 grams of Sodium atoms.

Sample Problem 8 What is the mass of 4 moles of Aluminum atoms?

Determine the number of iron atoms in a piece of iron weighing 2.8 grams.

Sample Problem 9 If one mole of Carbon atoms weigh 12 grams, what is mass in grams of a single atom of Carbon?

Sample Problem 10. Calculate the mass of 0.5 mole of N2 gas.

Sample Problem 11. Convert 12.044 X 10²² molecules of Sulphur dioxide into moles?

Sample Problem 12. In which case the number of Hydrogen atoms is more- 2 mol of HCl or 1 mol of NH3?

Sample Problem 13 . An ornament of silver contains 20 gram silver. Calculate the moles of silver present.

Sample Problem 14. If 1 g sulphur dioxide contains x molecules, what will be the number of molecules in 1 g of methane?

Sample Problem 15. Calculate the number of aluminium ions present in 0.051 g of aluminium oxide.

Sample Problem 16. How many grams of neon will have the same number of atoms as 4 g of calcium?

Sample Problem 17. Calculate the number of iron atoms in a piece of iron weighing 2.8 grams.

Sample Problem 18. What is the mass of 3 moles of Zinc?

Sample Problem 19 : What is the ratio of molecules present in 6.6 grams of CO2 and 3.2 grams of SO₂?

Sample Problem 20. If one gram of Sulphur contains x atoms, what will be the number of atoms in one gram of oxygen? (atomic mass of S = 32u) 

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