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A2 CHEMISTRY > EEE past paper questions > Flashcards

EEE past paper questions Flashcards

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1
Q

Equation for reaction when ammonia is heated with oxygen to form NO

A

4NH3 + 5O2 –> 4NO + 6H2O

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2
Q

How to determine initial rate of reaction using graph

A

Tangent at t = 0

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3
Q

What is bronsted-lowry acid?

A

A proton donor

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4
Q

Large scale uses for hydrogen

A

Production of ammonia
Hydrogenation of ethene
Fuel or fuel cells

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5
Q

When presented with table of redox half equations and electrode potentials, why is HCl not suitable for acidifying potassium manganite solution for titration (H2SO4 is)

A

electrode potential for MnO4 system is more positive than for Cl2 system
MnO4- oxidises Cl- to form Cl2 giving incorrect results
and either: MnO4- does not react with SO42- because sae sides of half equation or there is no SO32- in H2SO4 to react with MnO4-

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6
Q

Two advantages of vehicles using fuel cells

A

Less CO2 or less greenhouse gases produced

Greater efficiency

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7
Q

3MnO4 2- + 2H2O 2MnO4 - + MnO2 + 4OH-

how can equilibrium position be shifted by bubbling CO2 gas through the mixture?

A

CO2 reacts with H2O forming acid : H2O + CO2 -> H2CO3
then the acid reacts with hydroxide ions: H2CO3 + OH- -> H2O + HCO3-
Equilibrium shifts to right to restore the OH-

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8
Q

Explain why enthalpy change of hydration of magnesium ions is more exothermic than for calcium ions

A

Magnesium ions have greater charge density because they are smaller ions
Thus, the have stronger bonding with H2O because greater electrostatic attraction

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9
Q

Reaction between ammonia and oxygen to make NO

A

2NH3 + 2.5O2 -> 2NO + 3H2O

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10
Q

Two large scale uses for hydrogen

A

Production of ammonia, hydrogenation of ethene, fuel or fuel cells

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11
Q

What is d block element?

A

elements who’s highest energy sub shell is a d-sub shell

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12
Q

KOH electrolyte decomposes forming H2 at one electrode and O2 at the other, predict the half equations

A

4OH- -> O2 + 2H2O + 4e-

2H2O + 2e- -> H2 + 2OH-

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13
Q

CO + 2H2 CH3COH

Temp increased, pressure constant, Kc decreased, what happened to equilibrium?

A

Equilibrium shifts to left

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14
Q

suggest why methanol is added to petrol?

A

adds oxygen

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15
Q

1st electron affinity of oxygen is negative, second is positive. Why is second positive?

A

Oxide ion and electron are both negative, so energy is required to overcome the repulsion

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16
Q

Describe with examples, equation and observations, the reaction transition metals undergo

A
  • Ligand sub. reactions
    eg. copper aqua complex (2+) + 4Cl-
    blue solution turns green then yellow
  • Precipitation reactions
    e.g Cu(s) + 2OH- -> copper hydroxide
    Blue solution forms blue precip
  • Redox reactions
    MnO4- + 8H+ + 5Fe2+ - -> Mn 2+ + 4H20 + 5Fe3+
    purple to pale yellow
17
Q

Describe the different shapes and stereoisomers shown by complex ions with examples

A
  • Tetrahedral
    CuCl4 2-
  • Octahedral
    Co(NH3)4Cl2 + which forms cis and trans isomers
  • square planar
    NiCl2NH3 (also forms cis and trans isomers)
    Optical isomers formed by complexes with multidentate ligands
18
Q

What does value ok Ka tell you about an acid?

A

It’s strength

19
Q

How do you choose an acid to make a buffer with if you have pKa values ?

A

Choose an acid with a pKa value closest to the target pH

20
Q

Same amount (moles) of HCl (strong) and Ethanoic (weak) acid reacted with same amount of magnesium. Explain why same volume of gas produced but reaction slower with ethanoic?

A

HCl and ethanoic acid release the same number of moles of H+ - stoichiometry of reactions: (from equations)
But because HCl is a stronger acid than ethanoic acid, conc. H+ was greater in its reaction so rate was faster

21
Q

Advantages of using the pH scale to measure conc. of H+ in acid

A

pH makes numbers more manageable/removes very small numbers

22
Q

Why is it difficult to predict whether lattice enthalpy of magnesium sulphide would be more or less exothermic than LE of sodium oxide [4]

A

Magnesium 2+ has greater nuclear charge than sodium +(and is smaller) so has greater charge density
S2- is larger than O2- so it has smaller charge density. Mg2+ has stronger attraction than Na+ but S2- has weaker attraction than O2-

23
Q

Why is it difficult to determine the lattice enthalpy of Na2CO3 using a born haber cycle?

A

Carbonate ion contains C and O, cycle needs formation of CO32- from C and O

24
Q

Methods being developed to store hydrogen for possible use as a fuel in cars

A

Adsorbed on a solid or stored as a liquid under pressure

25
Q

Kc = [A]/[B]^2 pressure is doubled, explain in terms of Kc, the effect of the conc.s of A and B when equilibrium has been reached

A
  • Kc doesn’t change with pressure
  • [NO2]^2 increases more than [N2O4]
  • equilibrium shifts to right so [N2O4] increases to maintain Kc
26
Q

Explain the term standard electrode potential as applied to the reduction of aqueous halogens

A

The e.m.f of a halogen reduction half cell consisting of Pt foil with a standard hydrogen half cell measured at 298 K conc. 1 mol dm ^-3 and gas pressure 1 Atm immersed in a solution of an aqueous halogen and halide ions

27
Q

Li (s) –> Li+ (s) + e- standard electrode potential = -3.04 V
Explain why there is no water in a lithium cell and include an equation

A

Lithium is highly reducing because it has a highly negative standard electrode potential.
2Li (s) + 2H2O –> H2(g) + 2LiOH
H2 gas is highly flammable

28
Q

State one important difference between a fuel cell and a conventional electrochemical cell, write equation for overall reaction that takes place in a hydrogen fuel cell, state two ways that hydrogen may be stored as a fuel for cars and suggest why some people consider the that the use of hydrogen as a fuel for cars consumes more energy than using fossil fuels (June 2010)

A
  • A fuel cell converts energy from reaction of a fuel with oxygen into a voltage/electrical energy
  • 2H2 + O2 –> 2H2O
  • under pressure as liquid or adsorbed onto surface of a solid
  • Energy is needed to make the hydrogen
29
Q

Explain in terms of Kc why equilibrium yield of C increases when pressure is increased:
Kc = [C]^2/[A][B]^3

A

Kc does not change with pressure, bottom term of Kc expression increases more than top when pressure is increased, [C] increases and bottom decreased until Kc is reached to maintain Kc

30
Q

Enthalpy change neut reaction, 35 cm^3 of 2.4 mol dm^3 HCl used, temp rise was 16.5
Repeated with 70 cm^3 of 1.2 mol dm^3, why will temp rise be less and predict it

A

Same energy is spread over a larger volume

around 11

A2 CHEMISTRY (16 decks)

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