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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The elements of the third period of the Periodic Table form chlorides of general formula ECl x where E represents the element. These chlorides show a variation in oxidation number from sodium to sulfur. Use the information given to complete the table below. formula of chloride NaCl MgCl 2 Al Cl 3 SiCl 4 PCl 3 SCl 2 oxidation number of element in the chloride By considering the electron configurations of the elements, explain the variation in oxidation number in the chlorides from Na to Al and from Si to S. Na to Al Si to S Sodium hydride, NaH, is a colourless crystalline solid which melts at 800 °C and has the same crystal structure as sodium chloride which has a melting point of 808 °C. When molten sodium chloride is electrolysed using graphite electrodes, a shiny deposit, D, forms on the cathode and a greenish-yellow gas is evolved from the anode. When molten sodium hydride is electrolysed, under suitable conditions using graphite electrodes, the same shiny deposit D is formed on the cathode and a colourless gas, G, is evolved from the anode. Describe with the aid of a diagram the bonding in a sodium chloride crystal. Suggest the type of bonding that is present in sodium hydride. What is the oxidation number of hydrogen in sodium hydride? Draw a ‘dot-and-cross’ diagram for sodium hydride. Show outer electrons only. The metals magnesium and aluminium form hydrides with formulae MgH2 and Al H3. The non-metals phosphorus and sulfur form hydrides with formulae PH3 and H2S. By considering their positions in the Periodic Table, suggest oxidation numbers for these four elements in their hydrides. compound MgH2 Al H3 PH3 H2S oxidation number of element in the hydride At room temperature, the chlorides of sodium, magnesium and aluminium are all solids which dissolve in water. The hydrides of sodium, magnesium and aluminium are also solids which react with water with the rapid evolution of the same colourless gas G in each case. What is the pH of the solutions formed when separate samples of sodium chloride, magnesium chloride, and aluminium chloride are dissolved in water? chloride sodium magnesium aluminium pH Suggest an equation for the reaction between sodium hydride and water. Suggest a value for the pH of the solution formed in . At room temperature, the chlorides of silicon, phosphorus and sulfur are all low melting point solids or low boiling point liquids that can be seen to react with water. Suggest what type of bonding is present in sulfur dichloride, SCl 2. Write a balanced equation for the reaction between the chloride of silicon, SiCl 4, and water.
9701_w09_qp_22
THEORY
2009
Paper 2, Variant 2
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Gold is an unreactive metal that can only be oxidised under specific conditions. The standard electrode potential, E o, of Au3+/ Auis +1.50 V. Define the term standard electrode potential. Draw a fully labelled diagram of the apparatus that should be used to measure the standard cell potential, , of Au3+/ Auand HNO3/ NO. Include all necessary chemicals.  Some relevant half-equations and their standard electrode potentials are given. half-equation E o / V Au3++ 3e– Au+1.50 [AuCl 4]–+ 3e– Au+ 4Cl –+1.00 NO3 –+ 4H++ 3e– NO+ 2H2O+0.96 Write an ionic equation to show the spontaneous reaction that occurs when an electric current is drawn from the cell in . Calculate the of the reaction in .  = V Gold can be oxidised by a mixture of concentrated hydrochloricacid and concentrated nitric acid, known as aqua regia. Concentrated hydrochloric acid is 12 mol dm–3. Concentrated nitricacid is 16 mol dm–3. Explain why aquaregia is able to dissolve gold. In your answer, state and explain what effect the use of concentrated hydrochloricacid and concentrated nitricacid have on the E values of half-equations 2 and 3. Aqueous gold(chloride, AuCl 3, reacts with aqueous hydrogenperoxide, H2O2, under certain conditions, forming Au, O2 and HCl. A student carries out separate experiments using different initial concentrations of AuCl 3 and H2O2. The initial rate of each reaction is measured. The table shows the results that are obtained. experiment [AuCl 3] / mol dm–3 / mol dm–3 rate of production of O2/ dm3 minute–1 0.05 0.50 7.66 × 10–2 0.10 0.50 1.53 × 10–1 0.15 1.00 4.60 × 10–1 Write an equation for the reaction of AuCl 3 with H2O2. Determine the rate equation of the reaction. Show your reasoning, quoting data from the table. Use the results of experiment2 to calculate the value of the rate constant, k, for this reaction. Include the units of k.  rate constant, k =  units =  Al F3 is an ionic compound. The Born–Haber cycle for the formation of Al F3 is shown. Al 3++ 3F+ 3e– Al + 3FAl + 1.5F2Al + 1.5F2Al F3Al 3++ 3F–∆H3 ∆H2 ∆H1 ∆H4 ∆H5 ∆H6 Name the enthalpy changes labelled ∆H4 and ∆H6. ∆H4 = ∆H6 =  Use the data in the table and data from the Data Booklet to calculate the lattice energy of Al F3. process enthalpy change / kJ mol–1 Al → Al +326 Al → Al 3++5137 F→ F––328 Al + 1.5F2→ Al F3–1504  lattice energy of Al F3 = kJ mol–1 Scandiumfluoride, ScF3, is an ionic compound. Use data from the Data Booklet to suggest how the lattice energy of Al F3 compares with the lattice energy of ScF3. Explain your answer. Al F3 is sparingly soluble in water. The concentration of its saturated solution at 298 K is 6.5×10–2 mol dm–3. Write an expression for the solubility product, Ksp, of Al F3. Ksp = Calculate the numerical value of Ksp for Al F3 at 298 K.  Ksp =  
9701_m20_qp_42
THEORY
2020
Paper 4, Variant 2
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Use Carbon forms two stable oxides, CO and CO2. Lead forms three oxides: yellow PbO, black PbO2 and red Pb3O4. Carbon monoxide burns readily in air. Heating black lead oxide produces oxygen gas, leaving a yellow residue. Suggest a balanced equation for each reaction. Explain how these two reactions illustrate the relative stabilities of the +2 and +4 oxidation states down Group IV. Red lead oxide contains lead atoms in two different oxidation states. Suggest what these oxidation states are, and calculate the ratio in which they occur in red lead oxide. Predict the equation for the action of heat on red lead oxide. When red lead oxide is heated with dilute nitric acid, HNO3, a solution of lead(nitrate is formed and a black solid is left. Suggest an equation for this reaction. Explain how this reaction illustrates the relative basicities of the two oxidation states of lead. Both tin(oxide and tin(oxide are amphoteric. Write a balanced equation for the reaction between tin(oxide and aqueous sodium hydroxide.
9701_s07_qp_4
THEORY
2007
Paper 4, Variant 0
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