Chemistry Labs

International Chemistry Olympiad · 1990

Problems

  1. Problem 2Aqueous solutions of copper salts. The pH of a 1.00×10−21.00\times10^{-2} mol dm−3^{-3} copper(II) nitrate solution is 4.65. (2.1) Write the equation for the formation of the conjugate base of the hydrated CuX2+\ce{Cu^{2+}} ion. (2.2) Calculate the pKaK_a of the corresponding acid–base pair. (2.3) Given Ksp(Cu(OH)X2)=1×10−20K_{sp}(\ce{Cu(OH)2}) = 1\times10^{-20}, at what pH does Cu(OH)X2\ce{Cu(OH)2} start to precipitate? (2.4) Using E0(CuX+/Cu)=+0.52E^0(\ce{Cu+/Cu}) = +0.52 V and E0(CuX2+/CuX+)=+0.16E^0(\ce{Cu^{2+}/Cu+}) = +0.16 V, write the disproportionation of CuX+\ce{Cu+} and calculate its equilibrium constant. (2.5) Calculate the composition (mol dm−3^{-3}) of the solution obtained by dissolving 1.00×10−21.00\times10^{-2} mol of copper(I) in 1.0 dm31.0\ \mathrm{dm^3} of water.Solutions: 1