9.2. Periodicity of chemical properties of the elements in Period 3
A subsection of Chemistry, 9701, through 9. The Periodic Table: chemical periodicity
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Vanadium is a transition element in Period 4 of the Periodic Table. Define transition element. Vanadium shows typical chemical properties of transition elements, including variable oxidation states. State two other typical chemical properties of transition elements. Explain why transition elements have variable oxidation states. VO2 + can be reduced to V2+ by C2O4 2– in acidic conditions. equation 2 2VO2 + + 3C2O4 2– + 8H+ 2V2+ + 6CO2 + 4H2O In a titration, 25.00 cm3 of 0.0300 mol dm–3 VO2 +is added to 10 cm3 of dilute sulfuric acid. A solution of 0.0400 mol dm–3 C2O4 2–is then added from a burette until the end-point is reached. The titration is repeated and concordant results obtained, as shown in Table 3.1. Table 3.1 volume of C2O4 2–added / cm3 28.15 28.10 Show that these results are consistent with the stoichiometry of equation 2. An excess of C2O4 2– reacts with VO2 + to form a mixture of two octahedral complex ions. The complex ions are stereoisomers of each other. Each complex ion contains a V2+ cation and three C2O4 2– ions. Complete the diagram to show the three-dimensional structure of one of the complex ions. Include the charge of the complex ion. Use O O to represent a C2O4 2– ion. V V2+can be oxidised by H2O2. Table 3.2 gives some relevant data. Table 3.2 half-equation E o / V H2O2+ 2H++ 2e– 2H2O+1.77 VO2 ++ 2H++ e– VO2++ H2O+1.00 VO2++ 2H++ e– V3++ H2O+0.34 V3++ e– V2+–0.26 Identify the vanadium species that forms when an excess of H2O2reacts with V2+under standard conditions. Explain your answer with reference to the data in Table 3.2. Concentrated acidified H2O2 can react with V2+ to form red VO2 3+ ions. VO2 3+ contains vanadium combined with the peroxide anion, O2 2–. Deduce the oxidation state of vanadium in VO2 3+.
9701_m23_qp_42
THEORY
2023
Paper 4, Variant 2
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A transition element X has the electronic configuration 4s2 3d3. Predict its likely oxidation states. State the electronic configuration of the ion X3+. Potassium manganate(, KMnO4, is a useful oxidising agent in titrimetric analysis. Describe how you could use a 0.0200 mol dm–3 solution of KMnO4 to determine accurately the [Fe2+] in a solution. Include in your description how you would recognise the end-point in the titration, and write an equation for the titration reaction. A 2.00 g sample of iron ore was dissolved in dilute H2SO4 and all the iron in the salts produced was reduced to Fe2+. The solution was made up to a total volume of 100 cm3. A 25.0 cm3 portion of the solution required 14.0 cm3 of 0.0200 mol dm–3 KMnO4 to reach the end-point. Calculate the percentage of iron in the ore. Use [T High-strength low-alloy (HSLA) steels are used to fabricate TV masts and long span bridges. They contain very low amounts of phosphorus and sulphur, but about 1% copper, to improve resistance to atmospheric corrosion. When dissolved in nitric acid, a sample of this steel gives a pale blue solution. What species is responsible for the pale blue colour? Describe and explain what you would see when dilute aqueous ammonia is added to this solution.
9701_s06_qp_4
THEORY
2006
Paper 4, Variant 0
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