9701_w09_qp_21
A paper of Chemistry, 9701
Questions:
5
Year:
2009
Paper:
2
Variant:
1
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Examiner s Use Magnesium, Mg, and radium, Ra, are elements in Group II of the Periodic Table. Magnesium has three isotopes. Explain the meaning of the term isotope. A sample of magnesium has the following isotopic composition by mass. isotope mass % by mass 78.60 10.11 11.29 Calculate the relative atomic mass, Ar, of magnesium to four significant figures. Ar = ……………… For Examiner’s Use Radium, proton number 88, and uranium, proton number 92, are radioactive elements. The isotope 226Ra is produced by the radioactive decay of the uranium isotope 238U. Complete the table below to show the atomic structures of the isotopes 226Ra and 238U. number of isotopes protons neutrons electrons 226Ra 238U Radium, like other Group II elements, forms a number of ionic compounds. What is the formula of the radium cation? ……………… Use the Data Booklet to suggest a value for the energy required to form one mole of the gaseous radium cation you have given in from one mole of gaseous radium atoms. Explain your answer.
1. Atomic structure  →  1.2. Isotopes
2. Atoms, molecules and stoichiometry  →  2.1. Relative masses of atoms and molecules
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For Examiner’s Use Radium was discovered in the ore pitchblende by Marie and Pierre Curie in 1898, and the metal was first isolated by them in 1910. The metal was obtained by first reacting the radium present in the pitchblende to form insoluble radium sulfate which was converted into aqueous radium bromide. This solution was then electrolysed using a mercury cathode and a carbon anode. Radium has chemical reactions that are typical of Group II metals and forms ionic compounds. What is the characteristic feature of the electronic configurations of all Group II metals? Radium sulfate is extremely insoluble. From your knowledge of the simple salts of Group II metals, suggest another very insoluble radium salt. During their electrolysis of aqueous radium bromide, the Curies obtained radium at the cathode and bromine at the anode. Write half-equations for the two electrode reactions that take place during this electrolysis. anode cathode Describe what you would see when magnesium reacts with cold water, steam. Write an equation for the reaction with steam. For Examiner’s Use Radium reacts vigorously when added to water. Write an equation, with state symbols, for this reaction. State two observations that could be made during this reaction. Suggest the approximate pH of the resulting solution. ……………… Will the reaction be more or less vigorous than the reaction of barium with water? Explain your answer.
10. Group 2  →  10.1. Similarities and trends in the properties of the Group 2 metals, magnesium to barium, and their compounds
9. The Periodic Table: chemical periodicity  →  9.2. Periodicity of chemical properties of the elements in Period 3
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For Examiner’s Use Alkanes such as methane, CH4, undergo few chemical reactions. Methane will, however, react with chlorine but not with iodine. Relevant standard enthalpy changes of formation for the reaction of methane with chlorine to form chloromethane, CH3Cl, are given below. ∆H f o /kJ mol–1 CH4 –75 CH3Cl –82 HCl –92 Use the data to calculate ∆H reaction for the formation of CH3Cl. CH4 + Cl 2 → CH3Cl + HCl The corresponding reaction with iodine does not take place. Use bond energy data from the Data Booklet to calculate a ‘theoretical value’ for ∆Hreaction for the following equation. CH4 + I2 → CH3I + HI Suggest why this reaction does not in fact occur. For Examiner’s Use By using equations, describe the mechanism of the reaction between chlorine and methane to form chloromethane, CH3Cl. Identify, by name, the separate steps of the overall reaction. What is the intermediate organic species in this reaction? The energy of activation for the formation of CH3Cl is 16 kJ mol–1. Use this figure and your answer to to complete the reaction pathway diagram below showing the formation of CH3Cl from CH4 and Cl2. Show clearly the intermediate organic species and the final products. Indicate on your sketch the relevant enthalpy changes and their values. enthalpy progress of reaction CH4 + Cl2
11. Group 17  →  11.4. The reactions of chlorine
5. Chemical energetics  →  5.1. Enthalpy change, \(\Delta H\)
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For Examiner’s Use The structural formulae of six different compounds, A – F, are given below. Each compound contains four carbon atoms in its molecule. CH3CH=CHCH3 CH3CH2COCH3 CH2=CHCH2CH3 A B C CH3CH2CH(OH)CH3 HOCH2CH2CH2CH2OH CH3CH2OCH2CH3 D E F What is the empirical formula of compound E? ……………… Draw the skeletal formula of compound D. Structural formulae do not show all of the isomers that may exist for a given molecular formula. Which two compounds each show different types of isomerism and what type of isomerism does each compound show? Identify each compound by its letter. compound type of isomerism Compound D may be converted into compound C. What type of reaction is this? ……………………………………… What reagent would you use for this reaction? ……………………………………… What is formed when compound E undergoes the same reaction using an excess of the same reagent? ……………………………………… For Examiner’s Use Compound A may be converted into compound B in a two-stage reaction. CH3CH=CHCH3 → stage I intermediate → stage II CH3CH2COCH3 What is the structural formula of the intermediate compound formed in this sequence? Outline how stage I may be carried out to give this intermediate compound. What reagent would be used for stage II? ………………………………………… Compounds D and F are isomers. What type of isomerism do they show? …………………………………………
13. An introduction to AS Level organic chemistry  →  13.1. Formulas, functional groups and the naming of organic compounds
13. An introduction to AS Level organic chemistry  →  13.4. Isomerism: structural isomerism and stereoisomerism
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For Examiner’s Use Three organic compounds, G, H, and J, each have the empirical formula CH2O. The numbers of carbon atoms in their molecules are shown in the table. compound number of C atoms G H J In H and in J, the carbon atoms are bonded directly to one another. G gives a silver mirror when treated with Tollens’ reagent. H and J each give a brisk effervescence with Na2CO3. Identify G. ……………………………………… What functional group is common to both H and J? ……………………………………… Identify H. ……………………………………… Identify J. ……………………………………… When J is heated under reflux with acidified K2Cr2O7, the product, K, gives a red-orange precipitate with 2,4-dinitrophenylhydrazine reagent. Draw the structural formula of K, the compound formed from J. For Examiner’s Use When J is warmed with concentrated sulfuric acid, a cyclic compound, L, is formed. L has the molecular formula C6H8O4. Suggest a displayed formula for L. What type of reaction occurs when L is formed from J? ………………………………………
13. An introduction to AS Level organic chemistry  →  13.1. Formulas, functional groups and the naming of organic compounds
21. Organic synthesis  →  21.1. Organic synthesis
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