11. Group 17
A section of Chemistry, 9701
Listing 10 of 617 questions
The elements in Group 17, the halogens, and their compounds, show many similarities and trends in their properties. Some data are given for the elements fluorine to iodine. element bond energy / kJ mol–1 standard enthalpy change of atomisation, / kJ mol–1 boiling point of element / K boiling point of hydrogen halide / K fluorine, F–F chlorine, Cl –Cl bromine, Br–Br iodine, I–I Explain the meaning of the term standard enthalpy change of atomisation. For fluorine and chlorine, the enthalpy changes of atomisation are half the value of the bond energies. For bromine and iodine, the enthalpy changes of atomisation are much more than half the value of the bond energies. Suggest a reason for this difference. The standard enthalpy of formation of iodine monochloride, ICl, is –24.0 kJ mol–1. Use this information and the bond energies of iodine and chlorine to calculate the I–Cl bond energy. I–Cl bond energy = kJ mol–1 Explain the trend in the boiling points of the hydrogen halides, HCl, HBr and HI. Suggest why the hydrogen halide HF does not follow the trend in boiling points shown by HCl, HBr and HI. In an experiment, two of the halogens are represented as P2 and Q2. P2 combines with hydrogen on heating to form HP, which can be easily broken down into its elements. A solution of HP in water reacts with aqueous silver ions to form a yellow precipitate that is insoluble in dilute aqueous ammonia. Q2 combines explosively with hydrogen in sunlight to form HQ, which is stable to heat. A solution of HQ in water reacts with aqueous silver ions to form a white precipitate that is soluble in dilute aqueous ammonia. Identify the halogens P2 and Q2. P2 = Q2 = HP readily decomposes into its elements when heated but HQ is stable to heat. Explain this with reference to bond energies. Write an equation for the thermal decomposition of HP. Write ionic equations, including state symbols, for 1. the formation of the white precipitate on addition of aqueous silver ions to aqueous HQ, 2. the subsequent dissolving of this precipitate in dilute aqueous ammonia. Chlorine reacts directly with many elements to form chlorides. Three such compounds are MgCl 2, Al Cl 3 and SiCl 4. State and explain the pattern shown by the formulae of these three chlorides. Write equations to show the behaviour of each of these chlorides when added to water. MgCl 2 Al Cl 3 SiCl 4
9701_s16_qp_22
THEORY
2016
Paper 2, Variant 2
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The halogens, chlorine, bromine and iodine, and their compounds, show a variety of similarities and trends in their physical and chemical properties. Give the colours and states of chlorine, bromine and iodine at room temperature and pressure. halogen colour state chlorine bromine iodine The halogens become less volatile down the group. Explain this trend in volatility. The halogens are oxidising agents. State and explain the trend in oxidising power of the halogens. Concentrated sulfuric acid reacts with solid sodium halides. State any observations that would be made on addition of concentrated sulfuric acid to ● solid sodium chloride, ● solid sodium iodide. Give reasons for the difference in the observations in . The addition of concentrated sulfuric acid to solid sodium bromide, NaBr, produces brown fumes and an acidic gas that decolourises acidified potassium manganate(solution. This acidic gas is a significant contributor to acid rain. Write the equation for the reaction of concentrated sulfuricacid with sodiumbromide. An aqueous solution, Z, contains a mixture of sodium chloride and sodium iodide. Excess aqueous silver nitrate is added to Z in a test-tube. A yellow precipitate forms. Explain the colour of this precipitate. Aqueous ammonia is then added to the test-tube in . The mass of precipitate decreases. Explain this observation.
9701_s17_qp_23
THEORY
2017
Paper 2, Variant 3
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The elements in Group 17, the halogens, show trends in both their chemical and physical properties. The elements and their compounds have a wide variety of uses. At room temperature fluorine and chlorine are gases, bromine is a liquid and iodine is a solid. State the trend in the volatility of the Group 17 elements down the group. Explain this trend. Iodine, I2, can be displaced from NaI, by chlorine, Cl 2. Write an equation for this reaction. Silver nitrate solution, AgNO3, is added to separate solutions of NaI and NaCl. Precipitates form. An excess of aqueous ammonia is then added to both precipitates. Complete the table to give the colour and name of the precipitate formed in each reaction and the effect of the addition of an excess of aqueous ammonia to each of the precipitates formed. NaI+ AgNO3NaCl + AgNO3colour of precipitate name of precipitate effect of addition of an excess of aqueous ammonia to the precipitate  Write an ionic equation, including state symbols, to show the reaction occurring when AgNO3is added to NaI. Solid NaI reacts with concentrated sulfuric acid to form purple fumes of I2and hydrogensulfide gas, H2S. However, when solid NaCl reacts with concentrated sulfuricacid the only gas produced is HCl . Explain the difference in the reactions of concentrated sulfuricacid with NaI and with NaCl. Your answer should refer to the role of the sulfuric acid in each reaction. Chlorine is commonly used in water purification. When chlorine is added to water it reacts to produce a mixture of acids, one of which is chloric(acid, HCl O, a powerful oxidising agent. Explain the meaning of the term oxidising agent, in terms of electron transfer. Suggest an equation for this reaction of chlorine with water. Write an equation for the reaction of chlorine with hot aqueous sodiumhydroxide. Use oxidation numbers to explain why this is a redox reaction. equation 
9701_s18_qp_23
THEORY
2018
Paper 2, Variant 3
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