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Cards (62)
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)
