9701_w11_qp_41
A paper of Chemistry, 9701
Questions:
8
Year:
2011
Paper:
4
Variant:
1
Login to start this paper & get access to powerful tools
1
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? For Examiner’s Use 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 (*).
11. Group 17  →  11.2. The chemical properties of the halogen elements and the hydrogen halides
15. Halogen compounds  →  15.1. Halogenoalkanes
Open
2
For Examiner’s Use Acetals are compounds formed when aldehydes are reacted with an alcohol and an acid catalyst. The reaction between ethanal and methanol was studied in the inert solvent dioxan. H+ CH3CHO + 2CH3OH CH3CH(OCH3)2 + H2O ethanal methanol acetal A When the initial rate of this reaction was measured at various starting concentrations of the three reactants, the following results were obtained. experiment number [CH3CHO] / mol dm–3 [CH3OH] / mol dm–3 [H+] / mol dm–3 relative rate 0.20 0.10 0.05 1.00 0.25 0.10 0.05 1.25 0.25 0.16 0.05 2.00 0.20 0.16 0.10 3.20 Use the data in the table to determine the order with respect to each reactant. order with respect to [CH3CHO] order with respect to [CH3OH] order with respect to [H+] Use your results from part to write the rate equation for the reaction. State the units of the rate constant in the rate equation Calculate the relative rate of reaction for a mixture in which the starting concentrations of all three reactants are 0.20 mol dm–3. relative rate = For Examiner’s Use The concentration of the acetal product was measured when experiment number 1 was allowed to reach equilibrium. The result is included in the following table. [CH3CHO] / mol dm–3 [CH3OH] / mol dm–3 [H+] / mol dm–3 [acetal A] / mol dm–3 [H2O] / mol dm–3 at start 0.20 0.10 0.05 0.00 0.00 at equilibrium (0.20–x at equilibrium 0.025 Complete the second row of the table in terms of x, the concentration of acetal A at equilibrium. You may wish to consult the chemical equation opposite. Using the [acetal A] as given, 0.025 mol dm–3, calculate the equilibrium concentrations of the other reactants and products and write them in the third row of the table. Write the expression for the equilibrium constant for this reaction, Kc, stating its units. Kc = units = Use your values in the third row of the table to calculate the value of Kc. Kc =
8. Reaction kinetics  →  8.1. Rate of reaction
Open
3
For Examiner’s Use On the following diagram draw a clear labelled sketch to describe the shape and symmetry of a typical d-orbital. Although the five d-orbitals are at the same energy in an isolated atom, when a transition element ion is in an octahedral complex the orbitals are split into two groups. Draw an orbital energy diagram to show this, indicating the number of orbitals in each group. energy Use your diagram as an aid in explaining the following. • Transition element complexes are often coloured. • The colour of a complex of a given transition element often changes when the ligands around it are changed. For Examiner’s Use Heating a solution containing potassium ethanedioate, iron(ethanedioate and hydrogen peroxide produces the light green complex K3Fe(C2O4)3, which contains the ion [Fe(C2O4)3]3–. The structure of the ethanedioate ion is as follows. –O O– C O O C Calculate the oxidation number of carbon in this ion. Calculate the oxidation number of iron in [Fe(C2O4)3]3–. The iron atom in the [Fe(C2O4)3]3– ion is surrounded octahedrally by six oxygen atoms. Complete the following displayed formula of this ion. Fe O 3– O O In sunlight the complex decomposes into potassium ethanedioate, iron(ethanedioate and carbon dioxide. Use oxidation numbers to help you balance the following equation for this decomposition. K3Fe(C2O4)3 K2C2O4 + FeC2O4 + CO2
1. Atomic structure  →  1.3. Electrons, energy levels and atomic orbitals
2. Atoms, molecules and stoichiometry  →  2.3. Formulas
Open
4
For Examiner’s Use Write the equation for a reaction in which ethylamine, C2H5NH2, acts as a Brønsted-Lowry base. Ammonia, ethylamine and phenylamine, C6H5NH2, are three nitrogen-containing bases. Place these three compounds in order of basicity, with the most basic first. most basic least basic Explain why you have placed the three compounds in this order. Write an equation for a reaction in which phenol, C6H5OH, acts as a Brønsted-Lowry acid. The pKa values for phenol, 4-nitrophenol and the phenylammonium ion are given in the table. compound pKa OH 10.0 OH O2N 7.2 NH3 + 4.6 Suggest an explanation for the difference in the pKa values of phenol and nitrophenol. For Examiner’s Use Using the information in the table opposite, predict which of the following pKa values is the most likely for the 4-nitrophenylammonium ion. NH3 O2N + Place a tick (✓) in the box beside the value you have chosen. pKa 1.0 4.5 7.0 10.0 Explain your answer to part . Phenylamine can be converted to 4-nitrophenol by the following steps. B OH step 2 step 1 OH NO2 step 3 NH2 Suggest the identity of intermediate B by drawing its structure in the box above. Suggest reagents and conditions for the three steps in the above scheme. reagentconditions step 1 step 2 step 3
12. Nitrogen and sulfur  →  12.1. Nitrogen and sulfur
15. Halogen compounds  →  15.1. Halogenoalkanes
14. Hydrocarbons  →  14.2. Alkenes
Open
5
For Examiner’s Use Compound C has the molecular formula C7H14O. Treating C with hot concentrated acidified KMnO4produces two compounds, D, C4H8O, and E, C3H4O3. The results of four tests carried out on these three compounds are shown in the following table. test reagent result of test with compound C compound D compound E Br2decolourises no reaction no reaction Nafizzes no reaction fizzes I2+ OH–no reaction yellow precipitate yellow precipitate 2,4-dinitrophenylhydrazine no reaction orange precipitate orange precipitate State the functional groups which the above four reagents test for. Br2NaI2+ OH–2,4-dinitrophenylhydrazine Based upon the results of the above tests, suggest structures for compounds D and E. D, C4H8O E, C3H4O3 For Examiner’s Use Compound C exists as two stereoisomers. Draw the structural formula of each of the two isomers, and state the type of stereoisomerism involved. type of stereoisomerism
13. An introduction to AS Level organic chemistry  →  13.1. Formulas, functional groups and the naming of organic compounds
17. Carbonyl compounds  →  17.1. Aldehydes and ketones
Open
6
Proteins exist in an enormous variety of sizes and structures in living organisms. They have a wide range of functions which are dependent upon their structures. The structure and properties of an individual protein are a result of the primary structure – the sequence of amino acids that form the protein. Proteins are described as condensation polymers. Write a balanced equation for the condensation reaction between two glycine molecules, H2NCH2CO2H. Draw the skeletal formula for the organic product. X-ray analysis has shown that in many proteins there are regions with a regular arrangement within the polypeptide chain. This is called the secondary structure and exists in two main forms. State the two forms of secondary structure found in proteins. Draw a diagram to illustrate one form of secondary structure. For Examiner’s Use There are around 20 different common amino acids found in humans most of which have the same general structure. C R H2N H CO2H The nature of the group R affects which bonds are formed as the secondary structure of the protein is further folded to give the tertiary structure. Complete the table indicating the type of tertiary bonding that each pair of the amino acid residues is likely to produce. residue 1 residue 2 type of tertiary bonding –HNCH(CH2CH2CH2CH2NH2)CO– –HNCH(CH2CH2CO2H)CO– –HNCH(CH3)CO– –HNCH(CH3)CO– –HNCH(CH2SH)CO– –HNCH(CH2SH)CO– –HNCH(CH2OH)CO– –HNCH(CH2CO2H)CO–
13. An introduction to AS Level organic chemistry  →  13.3. Shapes of organic molecules; σ and π bonds
3. Chemical bonding  →  3.4. Covalent bonding and coordinate (dative covalent) bonding
Open
7
For Examiner’s Use One of the key areas of investigation in understanding the structures of polypeptides and proteins is the sequence of amino acids that make up the polypeptide chains. One of the methods used to determine the amino acids present in a polypeptide chain is electrophoresis. Sketch and label the apparatus used to carry out electrophoresis. In electrophoresis, different amino acids move in different directions and at different speeds. What factors determine the direction of travel of an amino acid? What factors determine the speed of movement of an amino acid? For Examiner’s Use Another important technique used to examine the structure of proteins is X-ray crystallography. In this technique the position of individual atoms can be determined, and the distances between them measured. Hydrogen atoms never produce images using X-ray crystallography. Explain why this is the case. Suggest and explain which one of the atoms in a molecule of cysteine, H2NCH(CH2SH)CO2H, would show up most clearly using X-ray crystallography.
13. An introduction to AS Level organic chemistry  →  13.3. Shapes of organic molecules; σ and π bonds
Open
8
For Examiner’s Use In today’s world we make use of a wide range of different polymers. These polymers are often substitutes for traditional materials, but may have more useful properties. Complete the table identifying one traditional material that has been replaced by each polymer. traditional material modern polymer and its use PVC in packaging Terylene in fabrics polycarbonate bottle Throwing away articles made from polymers after use is a major environmental concern for two main reasons. Identify each of these reasons and suggest a strategy that has been adopted to try to overcome each of these. reasons : strategy 1 : strategy 2 : For Examiner’s Use One suggestion for the disposal of polymers is to use them as a fuel to provide energy for small-scale power stations or district heating schemes. Identify one polymer which would be unsuitable for this use, explaining the reason behind this. polymer reason Polymers can be either thermoplastic or thermosetting. Name a thermoplastic polymer. State which type of polymerisation produces thermoplastic polymers, explaining your answer in terms of the structure of the polymer.
20. Polymerisation  →  20.1. Addition polymerisation
Open