J & K CET Medical J & K - CET Medical Solved Paper-2006

  • question_answer
    Consider the following abbreviations for hydrated alkali ions: \[X={{[Li{{({{H}_{2}}O)}_{n}}]}^{+}}\] \[Y={{[K{{({{H}_{2}}O)}_{n}}]}^{+}}\] \[Z={{[Cs{{({{H}_{2}}O)}_{n}}]}^{+}}\] What is the correct order of size of these hydrated alkali ions?

    A) \[X>Y>Z\]           

    B)  \[Z>Y>X\]

    C) \[X=Y=Z\]           

    D)  \[Z>X>Y\]

    Correct Answer: A

    Solution :

                     All alkali metal salts are soluble in water. The degree of hydration depends upon the size of the cation. Smaller the size of a cation greater is its charge density and hence, greater is its tendency to draw electrons from molecules which are thus polarised.\[L{{i}^{+}}\]ion being smallest in size among alkali metal ions is the most extensively hydrated while\[C{{s}^{+}}\]ion the largest alkali metal ion is the least hydrated. The size of hydrated alkali ions is as: \[L{{i}^{+}}>N{{a}^{+}}>{{K}^{+}}>R{{b}^{+}}>C{{s}^{+}}\] (Relative ionic radii in water) (Relative degree of hydration)


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