PAPER 1 Exam Qs

• • Octahedral complexes can display cis–trans isomerism (a special case of E–Z isomerism) with monodentate ligands and optical isomerism with bidentate ligands.
  • Transition metal ions commonly form tetrahedral complexes with larger ligands (eg Cl– ).
• Section 3.2.5.5: Variable oxidation states

  • Students are also expected to know the colours of the vanadium ions produced when a solution of ammonium vanadate(V) (NH4VO3 ) is reduced by zinc metal under acidic conditions.
  • Oxidation state V(V)
  • Species in acidic solution [VO2 (H2O)4 ] +
  • Colour of solution = yellow
• • Oxidation state of vanadium = V(IV)
  • Species in acidic solution = [VO(H2O)5 ] 2+
  • Colour of solution = Blue
• • Vanadium oxidation state = V(III)
  • Colour = green
• • Vanadium oxidation state = V(II)
  • Colour = purple
• State which of the elements magnesium and aluminium has the lower first ionisation energy. Explain your answer. [3 marks]

  • Al
  • Outer electron in 3p sublevel/orbital
  • Higher in energy/further from the nucleus so easier to remove (both needed to get M3)
• Another student used the same method and obtained a value for the enthalpy of reaction of −142 kJ mol−1

  A data book value for the enthalpy of reaction is −310 kJ mol−1 Suggest the most likely reason for the large difference between the student’s experimental value and the data book value.

  • HEAT LOSS from the apparatus would mean the experimental value is smaller/lower/LESS EXOTHERMIC than the data source
• Suggest how the students’ method, and the analysis of the results, could be improved in order to determine a more accurate value for the enthalpy of reaction.

  • Stage 1 Improved insulation
  • 1a Insulate the beaker or use a polystyrene cup or a lid
  • 1b To reduce heat loss
• Suggest how the students’ method, and the analysis of the results, could be improved in order to determine a more accurate value for the enthalpy of reaction.

  Stage 2 Improved temperature recording

  • 2a Record the temperature for a suitable time before adding the metal
  • 2b To establish an accurate initial temperature OR
  • 2c Record temperature values at regular time intervals
  • 2d To plot the temperature results against time on a graph
• Suggest how the students’ method, and the analysis of the results, could be improved in order to determine a more accurate value for the enthalpy of reaction.

  Stage 3 Improved analysis of results

  • 3a Extrapolate the cooling back to the point of addition
  • 3b To establish a (theoretical) maximum temperature OR temperature change (e.g. at the 4th minute) OR adjust for the cooling /apply a cooling correction
• Suggest two reasons why the SULFUR DIOXIDE by-product of this process is removed from the exhaust gases. [2 marks]

  • Prevents acid rain (which damages buidlings/ecology)
  • Toxic OR causes breathing problems
  • Reduces waste product
  • OR makes use of the waste
  • OR improves atom economy
  • OR Reduces need for sulfur mining
  • OR used to produce sulphuric acid
  • (OR any named products)
• State two differences between the ‘plum pudding’ model and the model of atomic structure used today. [2 marks]

  • Statement about the nucleus:
  • (Central) nucleus contains protons and neutrons. Statement about electrons:
  • Electrons are now arranged in energy levels/shells/orbitals
  • ADDITIONAL MP: no neutrons in plum pudding / neutrons now recognised

  
• State the meaning of the term first ionisation energy

  • Heat / enthalpy / energy for removal of one electron (1)
  • from a gaseous atom (1)
• Suggest why Aluminium hydroxide is insoluble in water.

  • Large lattice energy or strong covalent bonds
  • OR sum of hydration energies less than covalent bond energies
• For the element X in the ionic compound MX,

  explain the meaning of the term oxidation state.

  • Charge on the ion (or element or atom)
• Suggest one reason why particles with the same mass and velocity can be deflected by different amounts in the same magnetic field.

  • Size of the charge (on the ion)
  • different charges
  • different m/z
• Explain why nonane has a higher boiling point

  • Nonane has a greater VAN DER WAALS FORCES BETWEEN MOLECULES
  • nonane molecules pack closer together / more surface contact (because it is NOT branched)

  
• In terms of structure and bonding explain why the boiling point of bromine is different from that of magnesium.

  • M1 Bromine is (simple) molecular / simple molecules
  • M2 Magnesium is metallic / consists of (positive) ions in a (sea) of delocalised electrons
  • M3 Br2 has weak (van der Waals) forces between the molecules / weak IMFs
  • M4 so more energy is needed to overcome the Stronger (metallic) bonds or converse.
• Liquid range

  • M5 Mg has a much greater liquid range because forces of attraction in liquid / molten metal are strong(er) OR converse argument for Br2

  
• Explain how permanent dipole-dipole forces arise between hydrogen chloride molecules. [2 marks]

  • DIFFERENCE IN ELECTRONEGATIVITY leads to bond polarity
  • (dipoles don’t cancel the molecule has an overall permanent dipole)
  • and there is an attraction between ∂+ on one molecule and ∂- on another
• Identify the diagram in Figure 2 that shows the correct relative sizes of the ions in sodium fluoride. Justify your answer.

  • Sodium ions and fluoride ions have the SAME ELECTRONIC CONFIGURATION
  • Sodium ion has more protons so attracts outer electrons closer //
  • OR Sodium (ion) has more protons so stronger attractions for (outer) electrons

  
• SPEC = the Mr of a hydrated salt (eg magnesium sulfate) by heating to constant mass.

  The correct value for x is 10 Suggest a reason for the difference between the experimental value for x and the correct value.

  • Failure to drive off all the water
  • OR Failure to heat for long enough
  • OR Not heated to constant mass
• Finding Mr of a hydrated salt by heating to constant mass =

  Suggest how the procedure could be improved, using the same apparatus, to give a more accurate value for x Justify your answer. [2 marks]

  • Heat to constant mass / heat for longer / use a smaller mass ((M2 dependent on M1 ))
  • You can be sure all / more of the water has been driven off
• Some of the liquid injected did not evaporate because it dripped into the gas syringe nozzle outside the oven.

  Explain how this would affect the value of the Mr of Y calculated from the experimental results. [2 marks]

  • Lower volume recorded
  • (PV = nRT Rearrange, n = pV/RT; smaller moles)
  • (Mr = mass / moles, dividing by a smaller number gives you a ) greater Mr than the real Mr
• Explain how ions are detected and relative abundance is measured in a TOF mass spectrometer. [2 marks]

  • ion hits the detector / negative plate AND gains an electron
  • (relative) abundance is proportional to (the size of) the current
• There are two lone pairs of electrons on the oxygen atom in a molecule of oxygen difluoride (OF2). Explain how the lone pairs of electrons on the oxygen atom influence the bond angle in oxygen difluoride. [2 marks]

  • Lone pairs repel more than bond pairs
  • bond angle will be lower (than regular tetrahedral angle) / bond angle of 103-106 degrees
• • Van der Waals forces (Allow London forces, dispersion forces, induced dipole-dipole)
  • (Uneven distribution of electrons in) one molecule
  • INDUCES dipole IN neighbouring/another/nearby MOLECULE
  • symmetrical molecule / dipoles cancel
  • OR no hydrogens bonded to F (N or O), therefore no hydrogen bonding

  
• Describe how the molecules are ionised using electrospray ionisation. [3 marks]

  • (Sample is) dissolved (in a volatile solvent)
  • (Injected through) needle/nozzle/capillary at high voltage/positively charged
  • Each molecule/particle gains a proton/H
• The strength of the adsorption of reactants and products onto the surface of a transition metal helps to determine its activity as a heterogeneous catalyst.

  (i) Explain why transition metals which adsorb strongly are not usually good catalysts

  • Reactants cannot move on surface
  • products not desorbed
  • Active sites blocked
• Explain why transition metals which adsorb weakly are not usually good catalysts

  • Reactants not brought together
  • No increase in reactant concentration on catalyst surface
  • Reactants not held long enough for a reaction to occur
  • Reactant bonds not weakened
• 1.12 Acids and bases RP9 Suggest briefly a practical procedure that a student could use to obtain data from which pH curve could be plotted [3 marks]

  • Place a fixed volume of alkali in a flask or beaker
  • Add acid in small portions from a burette
  • STIR and use a pH meter to record the pH after each addition of acid
• The student was provided with samples of three different indicators

  Suggest how the practical procedure could be refined by the student to identify the most suitable indicator [2 marks]

  • Repeat the experiment with each indicator
  • Select the indicator that changes colour rapidly when the pH changes from about 7 to 4 (the vertical section of the pH curve)