The molarity of a 0.2 N Na2CO3 solution will be : - A ) 0.1 M , B ) 0.2 M , C ) 0.3 M , D ) None of these ,

1 ) The molarity of a 0.2 N  Na₂CO₃  solution will be : -

A ) 0.1 M ,                                                  B ) 0.2 M ,

C ) 0.3 M ,                                                  D ) None of these ,

Correct Answer : -   A ) 0.1 M ,   

Solution : -

2 ) The equivalent weight of a certain trivalent element is 20 . Molecular weight of its oxide is : -

A ) 150 ,                                                     B ) 168 ,

C ) 189 ,                                                     D ) None of these ,

Correct Answer : -   B ) 168 ,

 

3 ) There are two isotopes of an element with atomic mass Z . Heavier one has atomic mass ( Z + 2 )  and  lighter one has atomic mass ( Z – 1 ) , then abundance of lighter one is : -

Solution : -

( Z + 2 ) ( x )  +  ( Z – 1 )( 1 – x )  =  Z  ,

Zx + 2x – Zx + Z – 1 + x = Z ,

So ,  x = 1 / 3 .

So ,  ( Z + 2 )  =  ( 1 / 3 ) x 100  =  33.3 % .

And  ( Z – 1 )  =  1 – 33 %  =  67.6 % .

 

4 )  In an acidic medium dichromate ion oxidizes ferrous ion to ferric ion . If the gram molecular mass of potassium dichromate is 294 g , its equivalent mass is : -

A ) 46 ,                                                       B ) 49 ,

C ) 55 ,                                                       D ) None of these ,

Correct Answer : -    B ) 49 ,

Solution : -

Fig

Oxidation charge on ( Cr ) = 6 – 3 = 3 .

For two Cr atoms  =  3 x 2  =  6 .

Equivalent weight  =  molecular weight  /  n  =  294 / 6  =  49 .

 

5 )  What is concentration of nitrate ions , if equal volumes of  0.1 M  AgNO3  and  0.1 M  NaCl are mixed together ?

A ) 0.01 ,                                                    B ) 0.05 ,

C ) 0.12 ,                                                    D ) None of these ,

Correct Answer : -   B ) 0.05 ,

Solution : -

AgNO3  -------->  Ag⁺   +    NO3^-  .

So ,  AgNO3  has 2 ions  =  0.1 / 2  =  0.05  ,  Answer .