Question:

Identify the correct order of solubility in aqueous medium :

Updated On: Apr 18, 2024
  • $\ce{ Na2S > ZnS > CuS }$
  • $\ce{ CuS > ZnS > Na2S }$
  • $\ce{ZnS > Na2S > CuS }$
  • $\ce{Na2S < CuS > ZnS}$
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The Correct Option is A

Solution and Explanation

Ionic compounds are more soluble in water or in aqueous medium. According to Fajans' rule, Size of the cation increases the ionic character also increases. Ionic character oc size of cation (if anion is same) The order of size of cation is $Na^+ > Zn^{2+} > Cu^{2+}$ $\therefore \, \, \, $The order of ionic character and hence, of solubility in water is as $Na_2S > ZnS > CuS $
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Concepts Used:

D and F Block Elements

The d-block elements are placed in groups 3-12 and F-block elements with 4f and 5f orbital filled progressively. The general electronic configuration of d block elements and f- block elements are (n-1) d 1-10 ns 1-2 and (n-2) f 1-14 (n-1) d1 ns2 respectively. They are commonly known as transition elements because they exhibit multiple oxidation states because of the d-d transition which is possible by the availability of vacant d orbitals in these elements. 

They have variable Oxidation States as well as are good catalysts because they provide a large surface area for the absorption of reaction. They show variable oxidation states to form intermediate with reactants easily. They are mostly lanthanoids and show lanthanoid contraction. Since differentiating electrons enter in an anti-penultimate f subshell. Therefore, these elements are also called inner transition elements.

Read More: The d and f block elements