Q69 of 76 Page 122

Atomic hydrogen combines with almost all elements but molecular hydrogen does not. Explain

Atomic hydrogen is very reactive whereas molecular hydrogen is stable. This can be understood by the dissociation enthalpy of H2 which is very high (435.88 kJ mol–1).


So, from the dissociation enthalpy of H-H bond it is clear that H2 bond will not easily break and it is relatively inert at room temperature. Thus it will only combine with few elements.


On the other hand atomic hydrogen being a single species can combine with other elements easily at room temperature.


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67

In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the options given below each question.

Assertion (A) : Permanent hardness of water is removed by treatment with washing soda.


Reason (R) : Washing soda reacts with soluble magnesium and calcium sulphate to form insoluble carbonates.


(i) Statements A and R both are correct and R is the correct explanation of A.


(ii) A is correct but R is not correct.


(iii) A and R both are correct but R is not the correct explanation of A.


(iv) A and R both are false.


 68

In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the options given below each question.

Assertion (A) : Some metals like platinum and palladium, can be used as storage media for hydrogen.


Reason (R) : Platinum and palladium can absorb large volumes of hydrogen.


(i) Statements A and R both are correct and R is the correct explanation of A.


(ii) A is correct but R is not correct.


(iii) A and R both are correct but R is not the correct explanation of A.


(iv) A and R both are false.


 70

How can D2O be prepared from water? Mention the physical properties in which D2O differs from H2O. Give at least three reactions of D2O showing the exchange of hydrogen with deuterium.

 71

How will you concentrate H2O2? Show differences between structures of H2O2 and H2O by drawing their spatial structures. Also mention three important uses of H2O2.