Title DCC Part II - Final.pdf ✅

DChO Chemistry Competition 2024 – Part II National Mock Written by Dr. Chen and his team 1 Q1. [14%] An iodate mineral has the chemical formula of M(IO3)Zy, where M is a metal cation, and Z is an anion. The ratio of the three ions in the mineral is 1:1:y. The molar mass of the mineral is 255.46 g mol-1 . a. When 1.000 g of the mineral was heated gently, a vapor was produced with a density of 0.5588 g/L at 120.0 °C and 1.000 atm. The mass of the residue was measured to be 0.9647 g. What is the molar mass of the vapor? What is the possible identity of Z? b. 1.000 g of the mineral was dissolved in 30 mL of 2 mol/L HNO3. The resulting solution was made up of 100.0 mL with distilled water, forming a stock solution. 10.00 mL of this stock solution reacts with excess potassium iodide. The iodine formed was titrated with 0.1000 mol/L sodium thiosulfate solution. Assume that all iodine was formed in the reaction of iodate ions with iodide ions. Calculate the volume of sodium thiosulfate solution needed to react with the iodine produced.
DChO Chemistry Competition 2024 – Part II National Mock Written by Dr. Chen and his team 2 c. However, the metal ion Mn+ in this mineral also reacts with iodide ions to form additional iodine. Therefore, the actual volume of sodium thiosulfate solution required in the titration was found to be 27.40 mL. Calculate the number of moles of iodine produced by the reaction of one mole of metal ion Mn+ with excess iodide ions. d. Deduct the formula of the mineral by reasonable analysis with computation. e. Write down the balanced net ionic equation of Mn+ reacting with excess iodide.
DChO Chemistry Competition 2024 – Part II National Mock Written by Dr. Chen and his team 3 Q2. [12%] Histidine has the following structural formula: a. In an aqueous solution, histidine exists in the form of a zwitterion (electrically neutral) designated as HA. When the solution is acidified, histidine is protonated successively to form H2A+ and H3A2+. Draw the structural formula of the zwitterion form of HA. b. Calculate the pH of a 0.010 M HA solution. H3A2+: pKa1 = 1.82; pKa2 = 6.00; pKa3 = 9.17.
DChO Chemistry Competition 2024 – Part II National Mock Written by Dr. Chen and his team 4 c. Calculate the concentration of HClO4 required to establish a pH of 2.00 in a 0.010 M HA solution (solution X).