11. Group 17
A section of Chemistry, 9701
Listing 10 of 617 questions
The residues from organohalogen pesticides are known to be a major cause of the decline in numbers of different birds of prey in many countries. These residues are concentrated in birds at the top of food chains. Analysis of the bodies of birds of prey show that the pesticide residues accumulate in the fatty tissues of the birds. This is because of the high partition coefficient between the fat in the tissues and water found in blood. Explain what is meant by the term partition coefficient. A particular pesticide has a partition coefficient of 8.0 between the solvent hexane and water. If a 25 cm3 sample of water containing 0.0050 g of the pesticide is shaken with a 25 cm3 sample of hexane, calculate the mass of pesticide that will dissolve in the hexane layer. Compounds used as pesticides may contain bromine or chlorine. What would be the difference in the ratio of the M: M+2 peaks if the pesticide contained one chlorine rather than one bromine atom? If a given pesticide contains two chlorine atoms per molecule, deduce the relative heights of the M, M+2 and M+4 peaks. The following graph shows the occurrence of pesticide residues in the eggs of fish-eating birds of prey upstream and downstream of a paper mill at Castlegar on the Columbia River in Canada. Columbia River Basin downstream of Castlegar TEQs parts per trillion upstream of Castlegar Furan 2378TCDF Dioxin 2378TCDD Other Dioxins / Furans PCBs PCBs, the dioxin 2378TCDD, and the furan 2378TCDF all come from chemicals containing chlorine. Suggest which compounds are present directly as a result of the paper mill. By studying the data for 1994, suggest which chemicalcome from sources other than the paper mill. Compare the downstream data for 1994 with that for 1997. Suggest what might be responsible for the change. A molecule of 2378TCDD contains four chlorine atoms. How many molecular ion peaks would this compound show in its mass spectrum?
9701_w09_qp_42
THEORY
2009
Paper 4, Variant 2
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The gaseous hydrogen halides HCl, HBr and HI, may be prepared by reacting the corresponding sodium salt with anhydrous phosphoric(acid, H3PO4. When the sodium halide NaX was used, the following reaction occurred and a sample of gaseous HX was collected in a gas jar. NaX + H3PO4 NaH2PO4 + HX A hot glass rod was placed in the sample of HX and immediately a red/orange colour was observed. What is the identity of NaX? What gas, other than HX, would be formed if concentrated sulfuric acid were used with NaX instead of phosphoric(acid? Suggest why phosphoric(acid rather than concentrated sulfuric acid is used to make samples of HX from the corresponding sodium salt. Explain your answer.
9701_w10_qp_21
THEORY
2010
Paper 2, Variant 1
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The gaseous hydrogen halides HCl, HBr and HI, may be prepared by reacting the corresponding sodium salt with anhydrous phosphoric(acid, H3PO4. When the sodium halide NaX was used, the following reaction occurred and a sample of gaseous HX was collected in a gas jar. NaX + H3PO4 NaH2PO4 + HX A hot glass rod was placed in the sample of HX and immediately a red/orange colour was observed. What is the identity of NaX? What gas, other than HX, would be formed if concentrated sulfuric acid were used with NaX instead of phosphoric(acid? Suggest why phosphoric(acid rather than concentrated sulfuric acid is used to make samples of HX from the corresponding sodium salt. Explain your answer.
9701_w10_qp_22
THEORY
2010
Paper 2, Variant 2
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The halogens chlorine and bromine react readily with hydrogen. X2+ H22HX[X = Cl or Br] Describe how you could carry out this reaction using chlorine. Describe two observations you would make if this reaction was carried out with bromine. Use bond energy data from the Data Booklet to calculate the ΔH o for this reaction when X = Cl, ΔH o = kJ mol–1 X = Br. ΔH o = kJ mol–1 What is the major reason for the difference in these two ΔH o values? Some halogens also react readily with methane. CH4+ X2CH3X+ HXWhat conditions are needed to carry out this reaction when X is bromine, Br? Use bond energy data from the Data Booklet to calculate the ΔH o of this reaction for the situation where X is iodine, I. ΔH o = kJ mol–1 Hence suggest why it is not possible to make iodomethane, CH3I, by this reaction. Halogenoalkanes can undergo homolytic fission in the upper atmosphere. Explain the term homolytic fission. Suggest the most likely organic radical that would be formed by the homolytic fission of bromochloromethane, CH2BrCl. Explain your answer. The reaction between propane and chlorine produces a mixture of many compounds, four of which are structural isomers with the molecular formula C3H6Cl2. Draw the structural or skeletal formulae of these isomers, and indicate any chiral atoms with an asterisk (*).
9701_w11_qp_41
THEORY
2011
Paper 4, Variant 1
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The halogens chlorine and bromine react readily with hydrogen. X2+ H22HX[X = Cl or Br] Describe how you could carry out this reaction using chlorine. Describe two observations you would make if this reaction was carried out with bromine. Use bond energy data from the Data Booklet to calculate the ΔH o for this reaction when X = Cl, ΔH o = kJ mol–1 X = Br. ΔH o = kJ mol–1 What is the major reason for the difference in these two ΔH o values? Some halogens also react readily with methane. CH4+ X2CH3X+ HXWhat conditions are needed to carry out this reaction when X is bromine, Br? Use bond energy data from the Data Booklet to calculate the ΔH o of this reaction for the situation where X is iodine, I. ΔH o = kJ mol–1 Hence suggest why it is not possible to make iodomethane, CH3I, by this reaction. Halogenoalkanes can undergo homolytic fission in the upper atmosphere. Explain the term homolytic fission. Suggest the most likely organic radical that would be formed by the homolytic fission of bromochloromethane, CH2BrCl. Explain your answer. The reaction between propane and chlorine produces a mixture of many compounds, four of which are structural isomers with the molecular formula C3H6Cl2. Draw the structural or skeletal formulae of these isomers, and indicate any chiral atoms with an asterisk (*).
9701_w11_qp_42
THEORY
2011
Paper 4, Variant 2
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Questions Discovered
617