‹ Back to the paper
Answer the following.
Account for the following/Explain why: (1) exists but does not. (2) Fluorine is a stronger…
(i)[3.0]
Account for the following/Explain why:
(1) $\text{PCl}_5$ exists but $\text{NCl}_5$ does not.
(2) Fluorine is a stronger oxidising agent than chlorine.
(3) Bond enthalpy of $\text{F}_2$ is less than that of $\text{Cl}_2$.
(ii)[2.0]
Complete and balance the following reactions:
(1) $\text{FeSO}_4 + \text{H}_2\text{SO}_4 + \text{Cl}_2 \rightarrow$ _______ + _______
(2) $\text{P}_4 + \text{HNO}_3 \rightarrow$ _______ + _______ + _______
Answer
Answer (i)
AI1. Because phosphorus has vacant $3d$ orbitals to expand its octet, $\mathrm{PCl_5}$ exists; nitrogen has no $d$ orbitals, so $\mathrm{NCl_5}$ does not.
2. Because of its low bond dissociation enthalpy and very high hydration enthalpy of $\mathrm{F^-}$, fluorine has a more positive electrode potential, so it is a stronger oxidising agent.
3. Because of the strong repulsion between the lone pairs on the small F atoms, the F-F bond is weaker than the Cl-Cl bond.
Answer (ii)
AIEquations: $2\mathrm{FeSO_{4}} + \mathrm{H_{2}SO_{4}} + \mathrm{Cl_{2}} \longrightarrow \mathrm{Fe_{2}(SO_{4})_{3}} + 2\mathrm{HCl}$ $\mathrm{P_{4}} + 20\mathrm{HNO_{3}} \xrightarrow{\text{conc.}\text{,}\text{ }\text{hot}} 4\mathrm{H_{3}PO_{4}} + 20\mathrm{NO_{2}} + 4\mathrm{H_{2}O}$
(1) Chlorine oxidises $\mathrm{Fe^{2+}}$ to $\mathrm{Fe^{3+}}$.
(2) Hot concentrated nitric acid oxidises phosphorus to phosphoric acid.
From ISC 2018 Specimen Chemistry Paper 1, question 17(b).
Check your working with the Chemical equation balancer: balance any equation, ionic and redox ones too, with the atom count on each side.