What is the effect of adding HCl on a certain solution at equilibrium?


> 
> If we have 
>  $$\ce{CH3COOH + H2O <=> CH3COO- + H+}$$
>  what is the effect on acetate ions when adding each HCl and NaOH to the solution? (State why according to Le Chatelier's principle) 
> 
> 
> 


Le Chatelier's principle states that if any of conditions of a chemical reaction at equilibrium changes, the reaction will shift to a direction to oppose that change and restore the equilibrium.


I guess adding $\ce{HCl}$ will increase hydronium ion concentration so the reaction will be shifted to the left side, accordingly acetate ions concentration will decrease. If we add $\ce{NaOH}$, this will increase water concentration so the reaction will be shifred to the right side accordingly increasing the concentration of acetate ions.




You are absolutely correct. Adding $\ce{HCl}$ adds protons to the mix, which you can imagine as applying pressure on the right-hand side, which means that the reaction will shift backwards slightly and the acetate concentration will decrease. For $\ce{NaOH}$, you also need to consider the underlying equation:


$$\ce{H2O <=> H+ + OH-}$$


which will be shifted to the left by additional hydroxides. This means that the overall proton concentration decreases and you can imagine that as lifting a weight from the right-hand side: The reaction will shift forwards.


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