Question

D) Pop 6. Iron (II) hydroxide is a slightly soluble base. In which of the following would Fe(OH)2 be most soluble? (It is not necessary to know the Ksp for Fe(OH)2. Give your reasoning after your answer. A) 0.1M HCI B) 0.1M KOH C) 0.1M Ca(OH)2 D)O.1M FeCl2 E) NaCl

Answer 1

Let us first know ,what will happen when Fe(OH)2 is dissolved

Fe(OH)2<=>Fe+2+2(OH)-

Now let us see in which solutions it is dissolved

look at KOH and Ca(OH)2 which will be in equilibrium condition with OH- ions in the solution

so,as per Le-Chatliers principle when concentration is more on right hand side ,the reaction goes in the backward direction ,which will make Fe(OH)2 insoluble

And the same principle works for FeCl​​​2 also.FeCl2 will be in equilibrium with Fe+2and Cl- . Therefore in this case also it will be insoluble

Now with HCl when Fe(OH)2 is dissolved ,water and Fe(Cl)2 are formed .As we all know Fe+2 is unstable and it undergoes oxidation in water to give Fe+3 ,which will be a stable ion . Therefore ,Fe(OH)2 will be soluble in 0.1 M HCl rather than NaCl.