11. Group 17
A section of Chemistry, 9701
Listing 10 of 617 questions
The elements of Group VII of the Periodic Table show variation in their properties. Complete the table below, stating the colour of each element in its normal state at room temperature. halogen melting point / °C colour chlorine –101 bromine –7 iodine Briefl y explain why the melting points of the halogens increase from chlorine to iodine. The halogens form many interhalogen compounds in which two different halogens are combined. One such compound is bromine monochloride, BrCl. Complete the electronic confi gurations of chlorine and bromine. chlorine 1s22s22p6 bromine 1s22s22p6 Draw a 'dot-and-cross' diagram of the BrCl molecule. Show outermost electrons only. Interhalogen compounds like BrCl have similar properties to the halogens. By considering your answers to and , predict the physical state of BrCl at room temperature. Explain your answer. physical state explanation Suggest the colour of BrCl. Cl 2 and BrCl each react with aqueous KI. Describe what would be seen when Cl 2 is bubbled through aqueous KI for several minutes. initially after several minutes Construct an equation for the reaction that occurs. Suggest an equation for the reaction that occurs between BrCl and aqueous KI. How do Cl 2 and BrCl behave in these reactions?
9701_w13_qp_23
THEORY
2013
Paper 2, Variant 3
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Write equations, with state symbols, to defi ne the following. the C–Br bond energy in CH3Br the Al –Cl bond energy in Al Cl 3 Describe and explain the trend in bond energies of the bonds in Cl 2, Br2 and I2. Fluorine, F2, does not follow this trend. Suggest a possible reason why. Use data from the Data Booklet to calculate the enthalpy change of the following reaction. H2+ X2→ 2HXwhen X = Cl ∆H = kJ mol–1 when X = I ∆H = kJ mol–1 Use these results to describe and explain the trend in the thermal stabilities of the hydrides of Group VII. Bromine reacts with hot NaOHto give a solution which on cooling produces white crystals of compound A. A has the following percentage composition by mass: Na, 15.2; O, 31.8; Br, 53.0. The remaining solution contains mostly NaBr, with a little of compound A. Calculate the empirical formula of A. Construct an equation for the reaction between Br2 and hot NaOH.
9701_w13_qp_43
THEORY
2013
Paper 4, Variant 3
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Sodium chlorate(, NaCl O, is the active ingredient in commercial bleach. The concentration of chlorate(ions was determined by titration. • 10.0 cm3 of a bleach solution was diluted to 250 cm3 in a volumetric flask using distilled water. • Dilute sulfuric acid and an excess of potassium iodide solution were added to a 25.0 cm3 portion of this solution to liberate iodine. • The resulting solution required 20.80 cm3 of 0.100 mol dm–3 aqueous sodium thiosulfate solution to react with the iodine produced. The titration reactions are shown. Cl O– + 2I– + 2H+ → I2 + Cl – + H2O I2 + 2S2O3 2– → 2I– + S4O6 2– Calculate the concentration, in mol dm–3, of Cl O– ions in the bleach solution. concentration of Cl O– = mol dm–3 An indicator was used in the thiosulfate-iodine titration. Name a suitable indicator for this titration. State the expected colour change you would observe at the end-point in this titration. from to State when in the procedure you would add the indicator. The concentration of chlorate(ions can also be determined by adding an excess of hydrogenperoxide to the sample of bleach and measuring the volume of oxygen gas produced. H2O2 + NaCl O → NaCl + O2 + H2O water oxygen gas 100 cm3 measuring cylinder hydrogen peroxide 5.0 cm3 bleach When an excess of aqueous hydrogen peroxide was added to 5.0 cm3 of a different bleach solution, 82 cm3 of oxygen was produced at room temperature and pressure. Calculate the concentration of Cl O– ions in this bleach solution. concentration of Cl O– = mol dm–3 Trichlorocyanuric acid, C3Cl 3N3O3, acts as a chlorine buffer and disinfectant for swimming pools. It reacts with water to give chloric(acid, HCl O. C3Cl 3N3O3 + 3H2O C3H3N3O3 + 3HCl O Write the expression for Kc for this equilibrium. Kc = In outdoor swimming pools, the HCl O is decomposed by sunlight. The decomposition of HCl O is a redox reaction which forms a gas that relights a glowing splint. Describe and explain the effect of the decomposition of HCl O on the equilibrium in . State the effect on Kc. effect on Kc The decomposition of HCl O is a redox reaction. Suggest an equation for this reaction. The buffer solution in blood is a mixture of carbonic acid, H2CO3, and hydrogencarbonate ions, HCO3 –. Healthy blood has a pH of 7.40. H2CO3 + H2O HCO3 – + H3O+ Ka = 7.94 × 10–7 mol dm–3 Explain how this buffer system acts to control the blood pH. Include equations in your answer. A patient’s blood has a [HCO3 –] : ratio of 9.5 : 1. Calculate the pH of the patient’s blood. pH =
9701_w16_qp_41
THEORY
2016
Paper 4, Variant 1
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Sodium chlorate(, NaCl O, is the active ingredient in commercial bleach. The concentration of chlorate(ions was determined by titration. • 10.0 cm3 of a bleach solution was diluted to 250 cm3 in a volumetric flask using distilled water. • Dilute sulfuric acid and an excess of potassium iodide solution were added to a 25.0 cm3 portion of this solution to liberate iodine. • The resulting solution required 20.80 cm3 of 0.100 mol dm–3 aqueous sodium thiosulfate solution to react with the iodine produced. The titration reactions are shown. Cl O– + 2I– + 2H+ → I2 + Cl – + H2O I2 + 2S2O3 2– → 2I– + S4O6 2– Calculate the concentration, in mol dm–3, of Cl O– ions in the bleach solution. concentration of Cl O– = mol dm–3 An indicator was used in the thiosulfate-iodine titration. Name a suitable indicator for this titration. State the expected colour change you would observe at the end-point in this titration. from to State when in the procedure you would add the indicator. The concentration of chlorate(ions can also be determined by adding an excess of hydrogenperoxide to the sample of bleach and measuring the volume of oxygen gas produced. H2O2 + NaCl O → NaCl + O2 + H2O water oxygen gas 100 cm3 measuring cylinder hydrogen peroxide 5.0 cm3 bleach When an excess of aqueous hydrogen peroxide was added to 5.0 cm3 of a different bleach solution, 82 cm3 of oxygen was produced at room temperature and pressure. Calculate the concentration of Cl O– ions in this bleach solution. concentration of Cl O– = mol dm–3 Trichlorocyanuric acid, C3Cl 3N3O3, acts as a chlorine buffer and disinfectant for swimming pools. It reacts with water to give chloric(acid, HCl O. C3Cl 3N3O3 + 3H2O C3H3N3O3 + 3HCl O Write the expression for Kc for this equilibrium. Kc = In outdoor swimming pools, the HCl O is decomposed by sunlight. The decomposition of HCl O is a redox reaction which forms a gas that relights a glowing splint. Describe and explain the effect of the decomposition of HCl O on the equilibrium in . State the effect on Kc. effect on Kc The decomposition of HCl O is a redox reaction. Suggest an equation for this reaction. The buffer solution in blood is a mixture of carbonic acid, H2CO3, and hydrogencarbonate ions, HCO3 –. Healthy blood has a pH of 7.40. H2CO3 + H2O HCO3 – + H3O+ Ka = 7.94 × 10–7 mol dm–3 Explain how this buffer system acts to control the blood pH. Include equations in your answer. A patient’s blood has a [HCO3 –] : ratio of 9.5 : 1. Calculate the pH of the patient’s blood. pH =
9701_w16_qp_43
THEORY
2016
Paper 4, Variant 3
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Questions Discovered
617