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Q 11.     Calculate the number of aluminium ions present in 0.051 g of aluminium oxide.

Give, the mass of Aluminum Oxide = 0.051 g. The molecular mass of Aluminium Oxide = 2 x mass of Aluminium + 3 x mass of Oxygen.                                                                   = 2 x 27 + 3 x 16                                                                   = 102 g Number of Moles of Aluminium Oxide : Now, Since 1 mole of Aluminium Oxide contain 2 moles of Aluminium...

Q 10.     Calculate the number of molecules of sulphur (S8 ) present in 16 g of solid sulphur.

Given the mass of Sulphur = 16 g The molecular mass of the Sulphur molecule = 8 x 32 = 256 g. The number of moles of Sulphur molecule : Now  Number of molecules in 1 mole =  molecules So, The number of molecules in 0.0625 moles =  molecules.                                                                     =   Molecules. Hence there are  Sulphur molecules in  16 g of solid sulphur.  

Q 9.     What is the mass of:

  (b)     0.5 mole of water molecules?

The mass of 1 mole of water molecules = 18 g Thus, the mass of 0.5 mole of water molecules = 18 x 0.5                                                                   = 9.0 g  

Q 9.     What is the mass of:

  (a)     0.2 mole of oxygen atoms? 

 The mass of 1 mole of oxygen atoms = 16 g  The mass of 0.2 mole of oxygen atoms = 0.2 x 16 g                                                                 = 3.2 g

Q 8.     Convert into mole.

  (c)     22 g of carbon dioxide

Given Mass of the carbon dioxide = 22 g. The molecular mass of Carbon dioxide in grams  =  mass of Carbon + 2 * mass of Oxygen                                                                                =  12u + 2 * 16u                                                                                =  44u The number of mole :

Q 8.     Convert into mole. 

     (b)     20 g of water 

Given, Mass of water = 20 g The Molecular mass of the water  = 2 * Mass of Hydrogen + Mass of Oxygen                                                       = 2 * 1 + 16                                                       =  18 g. Now, Number of moles :

Q 8.     Convert into mole.

  (a)     12 g of oxygen gas 

The molecular Mass of the Oxygen = 32 g Now, Since 32 g Oxygen = 1 mole  The number of moles in 12 g Oxygen:

Q 7.     What is the mass of— 

   (c)     10 moles of sodium sulphite (Na2SO3 )?

The molecular mass of Sodium sulphite (Na2SO3 ) = 2 * 23 + 32 + 3 * 16                                                                                   = 126u  Mass of 10 moles of sodium sulphite = 10 x Mass of 1 mole of Na2SO3                                                             = 10 x molecular mass of Na2SO3 in grams                                                            = 10 x...

Q 7.     What is the mass of— 

   (b)     4 moles of aluminium atoms (Atomic mass of aluminium = 27)?

The atomic mass of Aluminium = 27 u. Mass of 4 moles of aluminium atoms = 4 x Mass of 1 mole of Al atoms                                                             = 4 x molecular mass of aluminum atoms in grams                                                             = 4 x 27                                                             = 108 g

Q 7.     What is the mass of—

   (a)     1 mole of nitrogen atoms?

 Atomic Mass of Nitrogen atom = 14 u.  Mass of one mole of nitrogen atoms = molecular mass of nitrogen atoms in grams                                                             = 14 g

Q 6.     Calculate the molar mass of the following substances.

   (e)     Nitric acid, HNO3

The molecular mass of  Nitric acid, HNO3  =  1 * Atomic Mass of N + 1 * Atomic Mass of H + 3 * Atomic Mass of O                                                                     =  1 * 14u + 1 * 1u + 3 * 16u                                                                     =  14u + 1u + 48u                                                                     =   63u  

Q 6.     Calculate the molar mass of the following substances.

  (d)      Hydrochloric acid, HCl

The molecular mass of Hydrochloric acid, HCl  =  1 * Atomic Mass of Cl + 1 * Atomic Mass of H                                                                             =  35.5 u +   1u                                                                            =  36.5u                                                                        

Q 4.     Calculate the molar mass of the following substances.

   (c)     Phosphorus molecule, P4

The molecular mass of  Phosphorus molecule, P4  =  4 * Atomic Mass of P                                                                                    =  4 * 31u                                                                                   =  124u                                                                                   

Q 6.     Calculate the molar mass of the following substances.

  (b)      Sulphur molecule , S8

The molecular mass of Sulphur molecule, =  8 * Atomic Mass of S                                                                     =  8 * 32u                                                                    =  256u                                                               

Q 6.     Calculate the molar mass of the following substances.

  (a)      Ethylene , C_{2}H_{2}

The molecular mass of ethyne,   =  2 * Atomic Mass of C + 2 * Atomic Mass of H                                                                 =  2 * 12u + 2 * 1u                                                                =  24u + 2u                                                                =   26u 

Q 5.     Give the names of the elements present in the following compounds.

             (a) Quick lime

             (b) Hydrogen bromide

             (c) Baking powder

             (d) Potassium sulphate.

The names of the elements present in the given compounds are :  (a) Quick lime :        = Calcium and Oxygen.  (b) Hydrogen bromide         = Hydrogen and Bromine.  (c) Baking powder        = Sodium, Hydrogen, Carbon, and Oxygen.  (d) Potassium sulphate.        = Potassium, Sulphur, and oxygen.

Q 4.      Write the chemical formulae of the following.

            (a) Magnesium chloride

            (b) Calcium oxide

            (c) Copper nitrate

            (d) Aluminium chloride

            (e) Calcium carbonate

The chemical formula of Given compounds are : (a) Magnesium chloride  (b) Calcium oxide (c) Copper nitrate (d) Aluminium chloride  (e) Calcium carbonate

Q 3.     What are polyatomic ions? Give examples.

Polyatomic ions are ions that contain more than one atom. These atoms can be of the same type or of a different type. Some examples of polyatomic ions are NH4+, OH-, SO42-, and SO32-.

Q 2.     When 3.0 g of carbon is burnt in 8.00 g oxygen, 11.00 g of carbon dioxide is produced. What mass of carbon dioxide will be formed when 3.00 g of carbon is burnt in 50.00 g of oxygen? Which law of chemical combination will govern your answer?

3.0 g of carbon combines with 8.0 g of oxygen to give 11.0 of carbon dioxide. So, by the law of definite proportions, When 3.00 g of carbon is burnt in 50.00 g of oxygen, only 8.00 g of oxygen will be used to produce 11.00 gram of carbon dioxide. The remaining 42.00 g of oxygen will remain unreacted. Law of constant proportion is Held.  

Q 1.     A 0.24 g sample of compound of oxygen and boron was found by analysis to contain 0.096 g of boron and 0.144 g of oxygen. Calculate the percentage composition of the compound by weight.

The total mass of the compound = 0.24 g Mass of boron in the compound = 0.096 g Mass of oxygen in the compound = 0.144 g Now, As we know, The percentage of an element in the compound :   So, The percentage of Boron in the compound by weight : The percentage of Oxygen in the compound by weight :
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