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A solution containing NH_(4)Cl and NH_(4)OH has [OH]=10^(-6) mol L^(-1), which of the following hydroxides would be precipitated when this solution in added in equal volume to a solution containing 0.1 M of metal ions?

Answer» <html><body><p>`Mg(OH)_(2) (K_(<a href="https://interviewquestions.tuteehub.com/tag/sp-1219706" style="font-weight:bold;" target="_blank" title="Click to know more about SP">SP</a>)=3xx10^(-<a href="https://interviewquestions.tuteehub.com/tag/11-267621" style="font-weight:bold;" target="_blank" title="Click to know more about 11">11</a>))`<br/>`Fe(OH)_(2) (K_(sp)=8xx10^(-16))`<br/>`Cd(OH)_(2) (K_(sp)=8xx10^(-<a href="https://interviewquestions.tuteehub.com/tag/6-327005" style="font-weight:bold;" target="_blank" title="Click to know more about 6">6</a>))`<br/>`AgOH(K_(sp)=5xx10^(-3))`</p>Solution :When equal volumes of `(NH_(4)Cl+NH_(4)OH)` and metal ions are mixed (volume becomes double and concentration is halved) <br/> `:. [OH]=(10^(6))/(2),[M^(+<a href="https://interviewquestions.tuteehub.com/tag/n-568463" style="font-weight:bold;" target="_blank" title="Click to know more about N">N</a>)]=(0.1)/(2)` <br/> `Q_(sp)` ( or `IP`) of metal hydroxides of `M(OH)_(2)` type <br/> `=[M^(+n)][OH]^(2)` <br/> `=((0.1)/(2))((10^(-6))/(2))^(2)=(1)/(8)xx10^(-13)` <br/> `=0.125xx10^(-13)=12.5xx10^(-11)` <br/> `:. Q_(sp) lt K_(sp)` of `Mg(OH)_(2) (1.25xx10^(-11)gt3xx10^(-11))` <br/> and `Q_(sp)gtK_(sp)` of `Fe(OH)_(2) (1.25xx10^(-11)gt8xx10^(-16))` <br/> So both can be precipitated. Since the `K_(sp)` of `Fe(OH)_(2)` is less than `K_(sp)` of `Mg(OH)_(2)`, so `Fe(OH)_(2)` will be precipitated <a href="https://interviewquestions.tuteehub.com/tag/first-461760" style="font-weight:bold;" target="_blank" title="Click to know more about FIRST">FIRST</a>. Similarly, `Q_(sp)` (or `IP`) of metal hydroxides of `M(OH)` type <br/> `=[M^(+1)][OH]=((0.1)/(2))((10^(-6))/(2))=0.25xx10^(-7)` <br/> `= Q_(sp)ltK_(sp)` of `AgOH(0.25xx10^(-7)lt5xx10^(-3))` <br/> It cannot be precipitated out. Hence `Fe(OH)_(2)` will be precipitated</body></html>


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