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Consider a solution of $\textrm{NH}_3$.

When $\textrm{NH}_4\textrm{Cl}$ is added (assume no volume change), would the $pH$ increase, decrease or remain constant? Why?


Increase. The addition of $\textrm{NH}_4^+$ shifts the equilibrium towards more $\textrm{NH}_3$ by Le Chatelier’s Principle. $\textrm{NH}_3$ is basic, the $pH$ will increase.


Increase. $\textrm{NH}_4^+$ is an acid. Adding more acid will increase the $pH$.


Remain constant. $\textrm{NH}_3$ is a weak base. The combination of a weak base and conjugate acid is a buffer. A buffer is by definition, a solution in which the $pH$ does not change.


Decrease. $\textrm{NH}_4^+$ is a weak acid. Adding more acid will increase the concentration of $\textrm{H}^+$ and thereby decrease the $pH$.


Decrease. $\textrm{Cl}^-$ would act as a base would decrease the $pH$.

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