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# Identify the correct order of solubility of $N{{a}_{2}}S, CuS,$ and $ZnS$ in aqueous medium: (A) $CuS$ > $ZnS$ > $N{{a}_{2}}S$ (B) $ZnS$ > $N{{a}_{2}}S$ > $CuS$ (C) $N{{a}_{2}}S$ > $CuS$ > $Zns$ (D) $N{{a}_{2}}S$ > $ZnS$ > $CuS$

Last updated date: 20th Jun 2024
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Hint: ‘Like dissolves like’ is a thumb rule for solubility. Water being a polar solvent, will dissolve the compound more which has a higher polarity. The solubility of solute in a solvent is determined by the balance of intermolecular forces between the solvent and solute, and the entropy change that occurs.

- The order of the size of the cation in $N{{a}_{2}}S$, CuS, and ZnS is:
$N{{a}^{+}}>Z{{n}^{+2}}>C{{u}^{+2}}$
Therefore the correct order of solubility is $N{{a}_{2}}S$ $> ZnS > CuS$, i.e option D.
Note: The solubility is favored by the entropy of mixing ($\Delta S$). The solubility depends on the enthalpy of dissolution ($\Delta H$) and the hydrophobic effect. Factors such as temperature and pressure also affect the solubility of a given solute in a solvent. Depending on the change in Gibbs free energy ($\Delta G$), the solubility of a given compound may increase or decrease with temperature. For most solids and liquids, the solubility increases with an increase in temperature. In water, at high temperature, the solubility of ionic solutes tends to decrease. The pressure dependence of solubility is usually neglected as it occasionally has practical significance.