11.2. The chemical properties of the halogen elements and the hydrogen halides
A subsection of Chemistry, 9701, through 11. Group 17
Listing 10 of 102 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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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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The Group17 elements, chlorine, bromine and iodine, are non-metals that show trends in their physical and chemical properties. Describe the trend in the colour of the Group17 elements down the group. The Group17 elements can oxidise many metals to form halides. Describe the relative reactivity of the elements in Group17 as oxidising agents. Chlorine reacts with hot tin metal to form tin(chloride, SnCl 4. SnCl 4 is a colourless liquid at room temperature that reacts vigorously with water to form an acidic solution. Suggest the type of structure and bonding shown by SnCl 4. Explain your answer. The Group 17 elements form soluble halides with sodium. Describe what is seen when dilute AgNO3is added to NaBrfollowed by aqueous ammonia. NaCl reacts with concentrated H2SO4 to form HCl and NaHSO4. Explain the difference between the reactions of concentrated H2SO4 with NaCl and with NaI. Your answer should refer to the role of the sulfuricacid in each reaction. The hydrogen halides are useful reagents in organic and inorganic reactions. Describe and explain the trend in the boiling points of the hydrogen halides, HCl, HBr and HI. Describe and explain the trend in the thermal stabilities of the hydrogen halides, HCl, HBr and HI. Lucas’s reagent is a mixture of HCl and ZnCl 2. Primary, secondary and tertiary alcohols can be distinguished by their reaction with Lucas’s reagent. Alcohols react with the HCl in Lucas’s reagent to form halogenoalkanes. ZnCl 2 acts as a homogeneous catalyst for these reactions. Explain the meaning of the term homogeneous. Pentan-3-ol, C2H5CH(OH)C2H5, reacts slowly with HCl to form a secondary halogenoalkane. Complete the equation for this reaction using structural formulae. C2H5CH(OH)C2H5 + ���������������������������������������������������������������������������������������������������� The fastest reaction shown by Lucas’s reagent is with a tertiary alcohol. Draw the structure of the tertiary alcohol that is an isomer of pentan-3-ol.  Tertiary alcohols tend to react with Lucas’s reagent using the same mechanism as in their reaction with HCl. Suggest the type of reaction shown by tertiary alcohols with Lucas’s reagent. 
9701_m20_qp_22
THEORY
2020
Paper 2, Variant 2
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In this question you can assume that 1H and 3H have the same chemical properties. A sample of ethanal contains only one isotope of hydrogen, 1H. It is reduced to compound Z, C2H6O, in a nucleophilic addition reaction using NaBH4. All the hydrogen atoms in the NaBH4 are the 3H isotope. NaBH4 CH3CHO C2H6O compound Z Compound Z is then oxidised back to ethanal and water. C2H6O + [O]  CH3CHO + H2O Which statement about the final mixture of products is correct?
9701_m21_qp_12
MCQ
2021
Paper 1, Variant 2
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Compounds P, Q and R have all been found in the atmosphere of one of Saturn’s moons. P C C N C C N Q C C H C N C H H H C N C R The equation for the complete combustion of P, C4N2, is shown. C4N2+ 4O2→ 4CO2+ N2∆H = –2036 kJ mol–1 The enthalpy change of formation, ∆Hf, of CO2is –384 kJ mol–1. Calculate the enthalpy change of formation, ∆Hf, of P, in kJ mol–1.  ∆Hf of P = kJ mol–1 One of the products of the complete combustion of P is nitrogen gas, N2. Explain the lack of reactivity of nitrogen. Q forms when HCN reacts with ethyne, H C C H. Ethyne, HCN and Q are all weak Brønsted–Lowry acids. Explain what is meant by the term weak Brønsted–Lowry acid. Ethyne, HCN and Q all contain triple bonds between two atoms. A triple bond consists of one sigma (σ) and two pi (π) bonds. Draw a labelled diagram to show the formation of one pi (π) bond.  P and Q can be detected in the atmosphere by infrared spectroscopy. Identify two absorptions, and the bonds that correspond to these absorptions, that will appear in the infrared spectra of both P and Q.  The flow chart shows some reactions of R. C H H H reaction 1 C N C R T CH3CH2CH2NH2 C C S H H H C N reaction 3 H2reaction 2 dilute H2SO4heat under reflux Name the type of reaction shown in reaction1. Draw the structure of S, the organic product of reaction2.  Name T. T can also be formed by the reaction of CH3CH2CH2Br with ammonia. State the necessary conditions of this reaction. 
9701_m21_qp_22
THEORY
2021
Paper 2, Variant 2
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This question is about the elements of Group VII, the halogens. Complete the following table. halogen colour physical state at room temperature chlorine bromine iodine Concentrated sulphuric acid is added to separate solid samples of magnesium chloride, magnesium bromide, and magnesium iodide. Describe, in each case, one observation you would be able to make. MgCl2 MgBr2 MgI2 Give an equation for the reaction of concentrated sulphuric acid with magnesium chloride. When dilute nitric acid and aqueous silver nitrate are added to a solution of a magnesium halide, MgX2, a pale cream precipitate is formed. This precipitate is soluble in concentrated aqueous ammonia but not soluble in dilute aqueous ammonia. What is the identity of the precipitate? Give an equation, with state symbols, for the reaction of the precipitate with concentrated aqueous ammonia. A hot glass rod is plunged into separate gas jars, one containing hydrogen chloride and one containing hydrogen iodide. For each gas, state what you would observe, if anything, and write an equation for any reaction that takes place. HCl HI Explain your answer to in terms of enthalpy changes. What is the role of the hot glass rod in any reaction that occurs?
9701_s06_qp_2
THEORY
2006
Paper 2, Variant 0
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