Q4 E - Chemistry (OpenStax)

Question

How do the concentrations of \(P{b^{2 + }}\)  \(and {S^{2 - }}\)  change when  \({K_2}\;S\)   is added to a saturated solution of PbS? 

Step-by-Step Solution

Answer

   The concentration of   \(\left[ {P{b^{2 + }}} \right] \;\)decreases, while \(\;\left[ {{S^{2 - }}} \right] \) decreases.

Step 1: To find the concentrations of \(\;Pb{\;^{2 + }}\) \(and {S^{2 - }}\) change when \({K_2}\;S\) is added to a saturated solution of PbS

The equilibrium will shift towards forming more PbS. Adding \({K_2}S\)  will increase

\(\left[ {{S^{2 - }}} \right]\) , therefore, the system will react by trying to minimize the stress (Le Chatelier's Principle).

STEP-2 : Applying Le Chatelier’s principle :

Le Chatelier’s principle explains that if  equilibrium is disturbed  by variations of conditions ,equilibrium position is shifted to balance change  in order to reestablish the equilibrium, hence the equilibrium is shifted towards forming more PbS, and thus addition of K₂S   would increase concentration of \(\left[ {{S^{2 - }}} \right]\).