The mass % of urea solution is 6 . The total weight of the solution is 1000 g . What is its concentration in $\mathrm{mol} \mathrm{L}^{-1}$ ? (Density of water $=1.0 \mathrm{~g} \mathrm{~mL}^{-1}$ )
( $\mathrm{C}=12 \mathrm{u}, \mathrm{N}=14 \mathrm{u}, \mathrm{O}=16 \mathrm{u}, \mathrm{H}=1 \mathrm{u}$ )
A non- volatile solute is dissolved in water. The $\Delta T_{\mathrm{b}}$ of resultant solution is 0.052 K . What is the freezing point of the solution ( in K )?
( $K_b$ of water $=0.52 \mathrm{~K} \mathrm{kgmol}^{-1}$,
$K_f$ of water $=1.86 \mathrm{~K} \mathrm{kgmol}^{-1}$,
freezing point of water $=273 \mathrm{~K}$ )
The standard reduction potentials of $2 \mathrm{H}^{+} / \mathrm{H}_2, \mathrm{Cu}^{2+} / \mathrm{Cu}, \mathrm{Zn}^{2+} / \mathrm{Zn}$ and $\mathrm{NO}_3^{-}, \mathrm{H}^{-} / \mathrm{NO}$ are 0.0 , +0.34 . -0.76 and 0.97 V respectively. Observe the following reactions
I. $\mathrm{Zn}+\mathrm{HCI} \rightarrow$
II. $\mathrm{Cu}+\mathrm{HCl} \rightarrow$
III. $\mathrm{Cu}+\mathrm{HNO}_3 \rightarrow$
Which reactions does not liberate $\mathrm{H}_2(g)$ ?