11.3. Some reactions of the halide ions
A subsection of Chemistry, 9701, through 11. Group 17
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Iodine is found naturally in compounds in many different oxidation states. Iodide ions, I–, react with acidified H2O2to form iodine, I2, and water. This reaction mixture is shaken with cyclohexane, C6H12, to extract the I2. Cyclohexane is immiscible with water. Identify the role of H2O2in its reaction with I– ions in acidic conditions. Write an ionic equation for the reaction. role ionic equation  15.0 cm3 of C6H12 is shaken with 20.0 cm3 of an aqueous solution containing I2 until no further change is seen. It is found that 0.390 g of I2 is extracted into the C6H12. The partition coefficient of I2 between C6H12 and water, Kpc, is 93.8. Calculate the mass of I2 that remains in the aqueous layer. Show your working.  mass of I2 in aqueous layer = g Suggest how the value of Kpc of I2 between hexan-2-one, CH3(CH2)3COCH3, and water compares to the value given in . Explain your answer. The Group1 iodides all form stable ionic lattices and are soluble in water. Define enthalpy change of solution. Use the data in Table1.1 to calculate the enthalpy change of solution of potassiumiodide, KI. Table 1.1 process enthalpy change, ∆H / kJ mol–1 K++ I–→ KI–629 K+→ K+–322 I–→ I––293  enthalpy change of solution = kJ mol–1 Suggest the trend in the magnitude of the lattice energies of the Group1 iodides, LiI, NaI, KI. Explain your answer. The concentration of Cu2+in a solution can be determined by the reaction of Cu2+ ions with I– ions. reaction 1 2Cu2+ + 4I– → 2CuI + I2 The I2 produced in reaction1 is titrated against a solution containing thiosulfate ions, S2O3 2–, using a suitable indicator. reaction 2 2S2O3 2– + I2 → S4O6 2– + 2I– A 25.0 cm3 portion of a Cu2+solution reacts with an excess of I–. The end-point of the titration occurs when 22.30 cm3 of 0.150 mol dm–3 S2O3 2–is added. Calculate the concentration of Cu2+in the original solution.  concentration of Cu2+= mol dm–3 Identify a suitable indicator for the titration. Copper(and copper(both contain electrons in all five 3d orbitals. Sketch the shape of a 3dxy orbital on the axes provided. z y x  The reaction of I– ions with persulfate ions, S2O8 2–, can be catalysed by Fe3+ ions. 2I– + S2O8 2– → I2 + 2SO4 2– Write equations to show how Fe3+ catalyses this reaction. An orange precipitate of HgI2 forms when Hg2+ ions are added to KI. The solubility of HgI2 at 25 °C is 1.00 × 10–7 g dm–3. Calculate the solubility product, Ksp, of HgI2. Include units in your answer. [Mr: HgI2, 454.4]  value of Ksp =  units =  
9701_m22_qp_42
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2022
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