Chemistry Labs

International Chemistry Olympiad · 1991

Problems

  1. Problem 1(1.1) Show that 0.1 mol of TlX2S\ce{Tl2S} dissolves in one litre of a 1 M solution of any strong monoprotic non-coordinating acid. (1.2) Show that 0.1 mol of CuS\ce{CuS} dissolves in 1 M HNOX3\ce{HNO3} but not in 1 M HCl\ce{HCl}. Data: E0(S/SX2−)=−0.48E^0(\ce{S/S^{2-}}) = -0.48 V; E0(NOX3X−/NO)=0.96E^0(\ce{NO3^-/NO}) = 0.96 V; pKa(HX2S)=7K_a(\ce{H2S}) = 7; pKa(HSX−)=13K_a(\ce{HS^-}) = 13; Ksp(TlX2S)=1×10−20K_{sp}(\ce{Tl2S}) = 1\times10^{-20}; Ksp(CuS)=1×10−35K_{sp}(\ce{CuS}) = 1\times10^{-35}; solubility of NO\ce{NO} in water (298 K): 2.53×10−22.53\times10^{-2} mol dm−3^{-3}. Assume that CuX2+\ce{Cu^{2+}} does not form stable complexes with ClX−\ce{Cl^-}.Solutions: 1