The $pH$ of a solution obtained by mixing $50 \, mL$ of $1 \, M \, HCl$ and $30 \, mL$ of $1 \, M \, NaOH$ is $x \times 10^{-4}$. The value of $x$ is ...... . (Nearest integer) $[\log 2.5 = 0.3979]$

$A$ certain amount of $H_2CO_3$ and $HCl$ are dissolved to form $1 \ L$ solution. At equilibrium,it is found that the concentrations of $H_2CO_3$ and $CO_3^{2-}$ are $0.1 \ M$ and $0.01 \ M$ respectively. Calculate the $pH$ of the solution. Given that for $H_2CO_3$,$K_{a_1} = 10^{-5}$ and $K_{a_2} = 10^{-8}$.

What is the ratio of the number of $H^{+}$ ions to the number of $H_2O$ molecules in $1 \ L$ of water?

What will be the change in acidity if
$(i)$ $CuSO_4$ is added in saturated $(NH_4)_2SO_4$ solution
$(ii)$ $SbF_5$ is added in anhydrous $HF$?

$100 \ cm^3$ of $0.1 \ N \ HCl$ solution is mixed with $100 \ cm^3$ of $0.2 \ N \ NaOH$ solution. The resulting solution is

Calculate the $pH$ of the resultant mixtures:
$(a)$ $10 \, mL$ of $0.2 \, M \, Ca(OH)_{2} + 25 \, mL$ of $0.1 \, M \, HCl$
$(b)$ $10 \, mL$ of $0.01 \, M \, H_{2}SO_{4} + 10 \, mL$ of $0.01 \, M \, Ca(OH)_{2}$
$(c)$ $10 \, mL$ of $0.1 \, M \, H_{2}SO_{4} + 10 \, mL$ of $0.1 \, M \, KOH$