WAEC Chemistry 2023 Paper

Concept:Chlorine is less reactive than fluorine, so it cannot displace fluorine from a fluoride salt.Explanation:Check each equation based on the actual chemical reactivity of chlorine.Option A is correct: $\mathrm{Ca(OH)_2 + Cl_2 \rightarrow CaOCl_2 + H_2O}$.This shows chlorine reacting with slaked lime to form bleaching powder.Option C is correct: $\mathrm{Cl_2 + 2NaOH \rightarrow NaCl + NaClO + H_2O}$.Chlorine disproportionates in cold dilute sodium hydroxide, giving chloride and hypochlorite ions.Option D is correct: $\mathrm{H_2S + Cl_2 \rightarrow 2HCl + S}$.Chlorine oxidises hydrogen sulphide to sulphur, so this reaction proceeds readily.Option B is incorrect: $\mathrm{Cl_2 + 2NaF \rightarrow 2NaCl + F_2}$.This equation claims that chlorine displaces fluorine from sodium fluoride.Fluorine is more electronegative and more reactive than chlorine.Fluorine can displace chlorine from chlorides, but chlorine cannot displace fluorine from fluorides.In reality, chlorine and fluorine react directly to form compounds such as chlorine trifluoride, $\mathrm{2Cl_2 + 3F_2 \rightarrow 2ClF_3}$.Answer:The equation that does not correctly illustrate one of the reactions of chlorine is $\mathrm{Cl_2 + 2NaF \rightarrow 2NaCl + F_2}$.