Problem 1
Assign oxidation number to the underlined elements in each of the following species: (a) \(\mathrm{NaH}_{2} \mathrm{PO}_{4}\) (b) \(\mathrm{NaH} \underline{\mathrm{S} O}_{4}\) (c) \(\mathrm{H}_{4} \mathrm{P}_{2} \mathrm{O}_{7}\) (d) \(\mathrm{K}_{2} \underline{\mathrm{Mn}} \mathrm{O}_{4}\) (e) \(\mathrm{Ca} \underline{\mathrm{O}}_{2}\) (f) \(\mathrm{NaB} \mathrm{H}_{4}\) (g) \(\mathrm{H}_{2} \underline{\mathrm{S}}_{2} \mathrm{O}_{7}\) (h) \(\operatorname{KAl}\left(\underline{\mathrm{S}} \mathrm{O}_{4}\right)_{2} \cdot 12 \mathrm{H}_{2} \mathrm{O}\)
Problem 3
Justify that the following reactions are redox reactions: (a) \(\mathrm{CuO}(\mathrm{s})+\mathrm{H}_{2}(\mathrm{~g}) \rightarrow \mathrm{Cu}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}(\mathrm{g})\) (b) \(\mathrm{Fe}_{2} \mathrm{O}_{3}(\mathrm{~s})+3 \mathrm{CO}(\mathrm{g}) \rightarrow 2 \mathrm{Fe}(\mathrm{s})+3 \mathrm{CO}_{2}(\mathrm{~g})\) (c) \(4 \mathrm{BCl}_{3}(\mathrm{~g})+\) 3LiAlH \(_{4}(\mathrm{~s}) \rightarrow 2 \mathrm{~B}_{2} \mathrm{H}_{6}(\mathrm{~g})+3 \mathrm{LiCl}(\mathrm{s})+3 \mathrm{AlCl}_{3}(\mathrm{~s})\) (d) \(2 \mathrm{~K}(\mathrm{~s})+\mathrm{F}_{2}(\mathrm{~g}) \rightarrow 2 \mathrm{~K}^{+} \mathrm{F}^{-}(\mathrm{s})\) (e) \(4 \mathrm{NH}_{3}(\mathrm{~g})+5 \mathrm{O}_{2}(\mathrm{~g}) \rightarrow 4 \mathrm{NO}(\mathrm{g})+6 \mathrm{H}_{2} \mathrm{O}(\mathrm{g})\)
Problem 4
Fluorine reacts with ice and results in the change: \(\mathrm{H}_{2} \mathrm{O}(\mathrm{s})+\mathrm{F}_{2}(\mathrm{~g}) \rightarrow \mathrm{HF}(\mathrm{g})+\mathrm{HOF}(\mathrm{g})\) Justify that this reaction is a redox reaction.
Problem 5
Calculate the oxidation number of sulphur, chromium and nitrogen in \(\mathrm{H}_{2} \mathrm{SO}_{5}\), \(\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}\) and \(\mathrm{NO}_{3}^{-}\). Suggest structure of these compounds. Count for the fallacy.
Problem 6
Write formulas for the following compounds: (a) Mercury(II) chloride (b) Nickel(II) sulphate (c) Tin(IV) oxide (d) Thallium(I) sulphate (e) Iron(III) sulphate (f) Chromium(III) oxide
Problem 7
Suggest a list of the substances where carbon can exhibit oxidation states from \(-4\) to \(+4\) and nitrogen from \(-3\) to \(+5\).
Problem 10
The compound \(\mathrm{AgF}_{2}\) is unstable compound. However, if formed, the compound acts as a very strong oxidising agent. Why?
Problem 11
Whenever a reaction between an oxidising agent and a reducing agent is carried out, a compound of lower oxidation state is formed if the reducing agent is in excess and a compound of higher oxidation state is formed if the oxidising agent is in excess. Justify this statement giving three illustrations.
Problem 12
How do you count for the following observations? (a) Though alkaline potassium permanganate and acidic potassium permanganate both are used as oxidants, yet in the manufacture of benzoic acid from toluene we use alcoholic potassium permanganate as an oxidant. Why ? Write a balanced redox equation for the reaction. (b) When concentrated sulphuric acid is added to an inorganic mixture containing chloride, we get colourless pungent smelling gas \(\mathrm{HCl}\), but if the mixture contains bromide then we get red vapour of bromine. Why?
Problem 13
Identify the substance oxidised reduced, oxidising agent and reducing agent for each of the following reactions: (a) \(2 \mathrm{AgBr}(\mathrm{s})+\mathrm{C}_{6} \mathrm{H}_{6} \mathrm{O}_{2}(\mathrm{aq}) \rightarrow 2 \mathrm{Ag}(\mathrm{s})+2 \mathrm{HBr}(\mathrm{aq})+\mathrm{C}_{6} \mathrm{H}_{4} \mathrm{O}_{2}(\mathrm{aq})\) (b) \(\begin{aligned} \mathrm{HCHO}(\mathrm{l})+2\left[\mathrm{Ag}\left(\mathrm{NH}_{3}\right)_{2}\right]^{+}(\mathrm{aq})+3 \mathrm{OH}^{-}(\mathrm{aq}) \rightarrow 2 \mathrm{Ag}(\mathrm{s})+\mathrm{HCOO}^{-}(\mathrm{aq})+4 \mathrm{NH}_{3} &(\mathrm{aq}) \\\\+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \end{aligned}\) (c) \(\mathrm{HCHO}(\mathrm{l})+2 \mathrm{Cu}^{2+}(\mathrm{aq})+5 \mathrm{OH}^{-}(\mathrm{aq}) \rightarrow \mathrm{Cu}_{2} \mathrm{O}(\mathrm{s})+\mathrm{HCOO}^{-}(\mathrm{aq})+3 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})\) (d) \(\mathrm{N}_{2} \mathrm{H}_{4}(\mathrm{l})+2 \mathrm{H}_{2} \mathrm{O}_{2}(\mathrm{l}) \rightarrow \mathrm{N}_{2}(\mathrm{~g})+4 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})\) (e) \(\mathrm{Pb}(\mathrm{s})+\mathrm{PbO}_{2}(\mathrm{~s})+2 \mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}) \rightarrow 2 \mathrm{PbSO}_{4}(\mathrm{~s})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})\)
