11. Group 17
A section of Chemistry, 9701
Listing 10 of 617 questions
Hydrogen halides are compounds formed when halogens (Group 17 elements) react with hydrogen. The bond polarity of the hydrogen halides decreases from HF to HI. Some relevant data are shown in the table. hydrogen halide HF HCl HBr HI boiling point / °C –85 –67 –35 H–X bond energy / kJ mol–1 Explain the meaning of the term bond polarity. Suggest why the boiling point of HF is much higher than the boiling points of the other hydrogen halides. Describe and explain the relative thermal stabilities of the hydrogen halides. The equation for the preparation of hydrogen chloride using concentrated sulfuric acid is shown. H2SO4 + NaCl NaHSO4 + HCl Use the Brønsted-Lowry theory of acids and bases to identify the base and its conjugate acid in this reaction. Explain your answer. Brønsted-Lowry base (base-= conjugate acid (acid-= Explain why the reaction of concentrated sulfuric acid and sodium iodide is not suitable for the preparation of hydrogen iodide. Hydrogen chloride undergoes a reversible reaction with oxygen. 4HCl + O22Cl 2+ 2H2OThe reaction is carried out at 400 °C in the presence of a copper(chloride catalyst. Use the data in the table to calculate the overall enthalpy change of reaction. compound enthalpy change of formation / kJ mol–1 HCl –92 H2O–242 enthalpy change of reaction = kJ mol–1 State the type of catalyst used in this reaction. Explain how a catalyst is able to increase the rate of a chemical reaction. The reaction exists in dynamic equilibrium. The reaction was repeated at 1000 °C and the same pressure. State and explain the effect on the composition of the equilibrium mixture of the change in temperature. When 1.60 mol of HCl are mixed in a sealed container with 0.500 mol of O2 at 400 °C, 0.600 mol of Cl 2 and 0.600 mol of H2O are formed. The total pressure inside the container is 1.50 × 105 Pa. ● Calculate the amounts, in mol, of HCl and O2 in the equilibrium mixture. HCl = mol O2 = mol ● Calculate the mole fraction of Cl 2 and hence the partial pressure of Cl 2 in the equilibrium mixture. mole fraction of Cl 2 = pCl 2 = Pa In a separate experiment, an equilibrium reaction mixture was found to contain the four gases at the partial pressures shown in the table. gas HCl O2 Cl 2 H2O partial pressure / Pa 4.8 × 104 3.0 × 104 3.6 × 104 3.6 × 104 Kp = (pCl 2)2 × (pH2O)2 (pHCl )4 × pO2 Use this information and the expression given for Kp to calculate a value for Kp. State the units of Kp. Kp = units = The reaction is repeated without a catalyst. State the effect of this on Kp.
9701_m17_qp_22
THEORY
2017
Paper 2, Variant 2
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Describe the trend in the reactivity of the halogens Cl 2, Br2 and I2 as oxidising agents. Explain this trend using values of E o (X2 / X–) from the Data Booklet. Write an equation for the reaction between chlorine and water. Use standard electrode potential, E o, data from the Data Booklet to calculate the for the following reaction. Cl 2 + 2OH– Cl – + Cl O– + H2O  = V The [OH–] was increased and the Ecell was measured. Indicate how the value of the Ecell measured would compare to the calculated in by placing one tick () in the table. Ecell becomes less positive than . Ecell stays the same as . Ecell becomes more positive than . Explain your answer.  A half-equation involving bromate(ions, BrO3 –, and bromide ions is shown. BrO3 –+ 3H2O+ 6e– Br –+ 6OH–E o = +0.58 V An alkaline solution of chlorate(, Cl O–, can be used to oxidise bromide ions to bromate(ions. Use the Data Booklet and the half-equation shown to write an equation for this reaction. Calculate the for the reaction in .  = V When a concentrated solution of bromic(acid, HBrO3, is warmed, it decomposes to form bromine, oxygen and water only. Write an equation for this reaction. The use of oxidation numbers may be helpful. 
9701_m18_qp_42
THEORY
2018
Paper 4, Variant 2
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The elements in Group17 of the Periodic Table are called the halogens. They form stable compounds with both metals and non-metals. The table gives some data about F2, HCl and CaF2. F2 HCl CaF2 boiling point / K relative formula mass 38.0 36.5 78.1 State what is meant by the term relative formula mass. F2 and HCl are both covalent molecules. Suggest why the boiling point of HCl is higher than that of F2. Explain why CaF2 has a very high boiling point. CaF2can be made by the reaction of calcium carbonate with hydrofluoric acid, HF. Write an equation for this reaction. Include state symbols. Complete the electronic configuration of a chloride ion. 1s2 When Cl 2 is passed over hot iron, FeCl 3 is formed. However, when I2is passed over hot iron, the following reaction occurs. Fe+ I2FeI2State what you would observe during the reaction between Fe and I2. Explain why FeI2is formed rather than FeI3. observation explanation  FeI2 is soluble in water. A student carries out a chemical test to confirm that a solution of FeI2 contains aqueous iodide ions, I–. The student adds a single reagent and a precipitate forms. Identify the reagent the student uses. State the colour of the precipitate that forms. reagent colour of precipitate  Compounds containing I– are often contaminated by bromide ions, Br –. Identify a further reagent that the student could use to show that the precipitate formed in contained iodide ions. HOF is the only known molecule that contains only the elements hydrogen, oxygen and fluorine. Draw a ‘dot-and-cross’ diagram to represent the bonding in a molecule of HOF. Show the outer shell electrons only.  HOF can be made by the reaction of F2 with ice at – 40 °C. The reaction is similar to the reaction of Cl 2 with cold water. Suggest an equation for the reaction of F2 with ice. HOF is an unstable compound and decomposes to form HF and O2. HOF → HF + 2 O2 ΔH = –139 kJ mol–1 Draw a fully labelled reaction pathway diagram on the axes provided to show the decomposition of HOF into HF and O2. enthalpy progress of reaction  Pure HF is a colourless liquid at 273 K. The liquid contains HF molecules that have strong hydrogen bonds between them. Draw a fully labelled diagram to suggest how a hydrogen bond can form between two HF molecules.  Interhalogen compounds, such as BrCl or IF5, contain two or more different halogen atoms that are covalently bonded. D is an interhalogen compound that contains only chlorine and fluorine. At 0 °C and 101 325 Pa, 1 dm3 of D has a mass of 4.13 g. Use the general gas equation to calculate the relative molecular mass, Mr, of D.  Mr =  Use your answer to to determine the molecular formula of D. If you were unable to calculate the Mr in , assume that the Mr is 130.5. This is not the correct value.  molecular formula of D =  
9701_m19_qp_22
THEORY
2019
Paper 2, Variant 2
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