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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Describe the trend in the solubility of the sulfates of magnesium, calcium and strontium. Explain your answer. > > most soluble least soluble Define lattice energy, ΔH latt. State and explain the main factors that affect the magnitude of lattice energies. Table 1.1 shows some energy changes. Table 1.1 energy change value / kJ mol–1 standard enthalpy change of atomisation of potassium +89 first ionisation energy of potassium +419 second ionisation energy of potassium +3070 standard enthalpy change of atomisation of sulfur +279 S–S bond energy +265 first ionisation energy of sulfur +1000 second ionisation energy of sulfur +2260 first electron affinity of sulfur –200 second electron affinity of sulfur +640 standard enthalpy change of formation of potassium sulfide K S381 Born–Haber cycles can be used to determine the lattice energies of ionic compounds. Complete the Born–Haber cycle in for potassium sulfide, K2S. Include state symbols for all of the species. 2K++ S+ 2e– 2K+ SK2SCalculate the lattice energy, ΔH o latt, of K2Susing relevant data from Table 1.1. Show your working. ΔH o latt of K2S= kJ mol–1 ,  ,
9701_s24_qp_42
THEORY
2024
Paper 4, Variant 2
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Write down what you would see, and write equations for the reactions that occur, when silicon(chloride and phosphorus(chloride are separately mixed with water. silicon(chloride phosphorus(chloride Iron(chloride, FeCl 3, is used to dissolve unwanted copper from printed circuit boards (PCBs) by the following reaction. 2FeCl 3+ Cu→ 2FeCl 2+ CuCl 2A solution in which [Fe3+] was originally equal to 1.50 mol dm–3 was re-used several times to dissolve copper from the PCBs, and was then titrated as follows. A 2.50 cm3 sample of the partially-used-up solution was acidifi ed and titrated with 0.0200 mol dm–3 KMnO4. This oxidised any FeCl 2 in the solution back to FeCl 3. It was found that 15.0 cm3 of KMnO4was required to reach the end point. Construct an ionic equation for the reaction between Fe2+ and MnO4 – in acid solution. State here the Fe2+ : MnO4 – ratio from your equation in . Calculate the number of moles of MnO4 – used in the titration. Calculate the number of moles of Fe2+ in 2.50 cm3 of the partially-used-up solution. Calculate the [Fe2+] in the partially-used-up solution. Calculate the mass of copper that could still be dissolved by 100 cm3 of the partially-used-up solution. mass of copper = g When SiCl 4 vapour is passed over Si at red heat, Si2Cl 6 is formed. Si2Cl 6 contains a Si-Si bond. The reaction of Si2Cl 6 and Cl 2 re-forms SiCl 4. Si2Cl 6+ Cl 2→ 2SiCl 4Use bond energy data from the Data Booklet to calculate ∆H o for this reaction. ∆H o = kJ mol–1 Calcium forms three calcium silicides, Ca2Si, CaSi and CaSi2. The fi rst of these reacts with water as follows. Ca2Si + H2O → Ca(OH)2 + SiO2 + H2 Balance this equation. You may fi nd the use of oxidation numbers helpful. During this reaction, state which elementhave been oxidised, which elementhave been reduced.
9701_w12_qp_41
THEORY
2012
Paper 4, Variant 1
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Write down what you would see, and write equations for the reactions that occur, when silicon(chloride and phosphorus(chloride are separately mixed with water. silicon(chloride phosphorus(chloride Iron(chloride, FeCl 3, is used to dissolve unwanted copper from printed circuit boards (PCBs) by the following reaction. 2FeCl 3+ Cu→ 2FeCl 2+ CuCl 2A solution in which [Fe3+] was originally equal to 1.50 mol dm–3 was re-used several times to dissolve copper from the PCBs, and was then titrated as follows. A 2.50 cm3 sample of the partially-used-up solution was acidifi ed and titrated with 0.0200 mol dm–3 KMnO4. This oxidised any FeCl 2 in the solution back to FeCl 3. It was found that 15.0 cm3 of KMnO4was required to reach the end point. Construct an ionic equation for the reaction between Fe2+ and MnO4 – in acid solution. State here the Fe2+ : MnO4 – ratio from your equation in . Calculate the number of moles of MnO4 – used in the titration. Calculate the number of moles of Fe2+ in 2.50 cm3 of the partially-used-up solution. Calculate the [Fe2+] in the partially-used-up solution. Calculate the mass of copper that could still be dissolved by 100 cm3 of the partially-used-up solution. mass of copper = g When SiCl 4 vapour is passed over Si at red heat, Si2Cl 6 is formed. Si2Cl 6 contains a Si-Si bond. The reaction of Si2Cl 6 and Cl 2 re-forms SiCl 4. Si2Cl 6+ Cl 2→ 2SiCl 4Use bond energy data from the Data Booklet to calculate ∆H o for this reaction. ∆H o = kJ mol–1 Calcium forms three calcium silicides, Ca2Si, CaSi and CaSi2. The fi rst of these reacts with water as follows. Ca2Si + H2O → Ca(OH)2 + SiO2 + H2 Balance this equation. You may fi nd the use of oxidation numbers helpful. During this reaction, state which elementhave been oxidised, which elementhave been reduced.
9701_w12_qp_42
THEORY
2012
Paper 4, Variant 2
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In a world with a rapidly increasing population, access to clean drinking water is critical. For many countries, groundwater sources, rather than stored rainwater or river-water, are vital. Groundwater is water that exists in the pore spaces and fractures in rock and sediment beneath the Earth's surface. The World Health Organisation (WHO) provides maximum recommended concentrations for different ions present in drinking water. The geological nature of the soil determines the chemical composition of the groundwater. The table shows some ions which may contaminate groundwater. ion present WHO maximum permitted concentration / mg dm–3 Ba2+ 0.30 Cl – 250.00 NO3 – 50.00 Pb2+ 0.01 Na+ 20.00 SO4 2– 500.00 Nitrate, NO3 –, ions are diffi cult to remove from groundwater. What is the reason for this? State which ions in the table above are likely to be removed from the water by treatment with powdered limestone, CaCO3, giving reasons for each of your answers. Nitrates and phosphates can enter water courses such as rivers or streams as a result of human activity. Both of these ions are nutrients for algae. What is the origin of these nitrates? Suggest an origin for the phosphates found in water courses. What effect do nitrates and phosphates have on water courses? Acid rain can have a major impact on natural waters, particularly lakes. In recent years there has been a worldwide effort to reduce the amount of acid rain produced. Write equations to show the production of acid rain from sulfur dioxide, SO2. The use of fossil fuels is one major source of sulfur dioxide. Name another major industrial source.
9701_w13_qp_41
THEORY
2013
Paper 4, Variant 1
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