When a person breathes rapidly during fear or excitement,the concentration of $CO_2$ in the blood decreases. What happens to the $pH$ of the blood?

Calculate the $pH$ of a buffer solution containing $0.027 \ M$ weak acid and $0.054 \ M$ of its salt with a strong base,if the $pK_{a}$ is $4.2$.

$0.1 \ mol$ of $CH_3NH_2$ $(K_b = 5 \times 10^{-4})$ is mixed with $0.08 \ mol$ of $HCl$ and diluted to $1 \ L$. The $[H^{+}]$ in the solution is:

Aqueous solutions of $HNO_{3}$, $KOH$, $CH_{3}COOH$, and $CH_{3}COONa$ of identical concentration are provided. The pair$(s)$ of solutions which form a buffer upon mixing is (are):

When $500 \, mL$ of $0.2 \, M$ acetic acid is added to $500 \, mL$ of $0.30 \, M$ sodium acetate solution,what is the $pH$ of the resulting solution? (Given: Dissociation constant of acetic acid $K_a = 1.5 \times 10^{-5}$)

$100 \ mL$ of $0.1 \ M$ $HA$ (weak acid) and $100 \ mL$ of $0.2 \ M$ $NaA$ are mixed. What is the $pH$ of the resultant solution? ($K_{a}$ of $HA$ is $10^{-5}$; $\log 2 = 0.3$)