TEST YOURSELF 1.7 Chemistry 9th Chapter 1

TEST YOURSELF 1.7

(1)How many atoms of Sodium are present in 3 moles of Sodium and what is the mass of it ?

Given data :

No of moles of sodium = 3 mol

No of sodium atoms = ?

Mass of sodium = ?

Solution :

No of sodium atoms = No of moles * N_A

No of sodium atoms = 3 * 6.02 * 10²³

                                      = 18.06 * 10²³ atoms

Mass of sodium = ?

Mass of sodium = No of moles * Molar mass

Mass of sodium =?

Mass of sodium = No of moles * Molar mass

                            = 3*23

                            = 69 grams

(2) How many atoms are in 1 amu and 1 g of hydrogen (H)?

Given Data :

Mass of Hydrogen = 1 amu

Mass of Hydrogen = 1 g

No. of Hydrogen atoms in both =?

Solution:

1 amu = 1.66* 10^-24 g

Number of hydrogen atoms =Mass of hydrogen atoms/Molar mass * N_A

                                                 = 1.66*10^-24/1 * 6.02*10²³

                                                 = 0.999 atoms

                                                 = 9.99*10^-1

                                                 = 1 atom

No. of hydrogen atoms in 1 gram=Mass of hydrogen/Molar mass*N_A

No. of atoms of Hydrogen in 1 g = 1/1 *6.02*10²³

                                                         = 6.02*10²³ atoms

(3) How many atoms are present in 16 g of O and 8 g of S?

Given Data :

Mass of O = 16 gram

Mass of S = 8 gram

No of atoms of both?

Solution :

No. of O atoms = Mass of O / Molar mass of O * N_A

No. of O atoms = 16/ 16 * 6.02*10²³

                           = 6.02*10²³ atoms

No. of Sulphur atoms = Mass of S / Molar mass of S * N_A

No. of S atoms = 8/ 32 * 6.02 *10²³

                          = 1.5 * 10²³ atoms

(4) Is the mass of 1 mole of O and 1 mole of S same?

1 atom of carbon means there is only 1 carbon atom. While 1 gram atom of carbon means the atomic mass of carbon expressed in grams which is 12g.

(5)  If 16 g of oxygen contains 1 mole of oxygen atoms calculate the mass of one atom of oxygen in grams.

1 mole of O atoms = 16 grams

Also, 1 mole of O atoms =  6.02*10²³ atoms of O

6.02*10²³ atoms of O has mass = 16 grams

1 atom of O has mass = 16 / 6.02*10²³ * 1

                                        = 2.65*10^-23 grams

(7) How many times is 1 mole of oxygen atom heavier than 1 mole of hydrogen atom?

1 mole of oxygen atom = 16 grams

1 mole of hydrogen atom = 1 gram

The ratio between these two will be 1:16

It means that 1 mole of oxygen atom is 16 times heavier than 1 mole of hydrogen atom.

(8) Why does 10 g nitrogen gas contain the same number of molecules as 10 g of carbon monoxide?

Mass of N₂ = 10 grams                            Mass of CO = 10 grams

Molar mass of N₂ = 28 g mol^-1                Molar mass of CO = 28 g mol^-1

No. of N₂ molecules =?                            No. of CO molecules = ?

No. of molecules of N₂                                             No. molecules of CO

= Mass of N₂/Molar mass*6.02*10²³     = Mass of CO/ Molar mass *N_A

= 10/28*6.02*10²³                                       = 10/ 28 *6.02*10²³

= 2.15*10²³  molecules                              = 2.15*10²³  molecules 

10 g nitrogen gas contain the same number of molecules as 10 g of  carbon monoxide because both have the same molar mass i.e. 28 g mol^-1