A solution which is $0.1 \mathrm{M}$ in $\mathrm{NaI}$ and $0.1 \mathrm{M}$ in ${\mathrm{Na}}_2\left({\mathrm{SO}}_4\right)$, is treated with solid $\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2$. Which compound, ${\mathrm{PbI}}_2$ or ${\mathrm{PbSO}}_4$, will precipitate first? What is the concentration of the anion of the least soluble compound, when the more soluble one starts precipitating?

Given: ${\mathrm{K}}_{\mathrm{sp}}\left({\mathrm{PbI}}_2\right)=8.7\times {10}^{-9}, {\mathrm{K}}_{\mathrm{sp}}\left({\mathrm{PbSO}}_4\right)=1.8\times {10}^{-8}$

Calculate the amount of ${\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4$ in grams, which must be added to $500 \mathrm{mL}$ of $0.2 \mathrm{M} {\mathrm{NH}}_3$, to yield a solution with $\mathrm{pH}=9.35, {\mathrm{K}}_{\mathrm{b}}\left({\mathrm{NH}}_3\right)=1.78\times {10}^{-5}, {10}^{-0.1}=0.79, \log 1.78=0.25$.

Give the answer correct up to one place of decimal without rounding-off.

The data of a chemical reaction $2\mathrm{A}\to \mathrm{P}$ is plotted as $1/\mathrm{C}$ vs time and the plot is a straight line(C is the concentration of A in mol/L). If the intercept is $2\times {10}^{-3} {\mathrm{mol}}^{-1} {\mathrm{dm}}^3$ and the slope$2\times {10}^{-2} {\mathrm{mol}}^{-1} {\mathrm{dm}}^3 {\mathrm{s}}^{-1}$, calculate the half-life period of the reaction.

A solution of $3.795 \mathrm{g}$ sulphur in $100 \mathrm{g}$ of ${\mathrm{CS}}_2$(b.p. $=46.3°\mathrm{C}$ ) boils at $46.66°\mathrm{C}$. Determine the formula of sulphur molecule in the solution.

${\mathrm{K}}_{\mathrm{b}}\left({\mathrm{CS}}_2\right)=2.42$