EEE past paper questions

Question 1

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

Answer 1

4NH3 + 5O2 –> 4NO + 6H2O

Question 2

How to determine initial rate of reaction using graph

Answer 2

Tangent at t = 0

Question 3

What is bronsted-lowry acid?

Answer 3

A proton donor

Question 4

Large scale uses for hydrogen

Answer 4

Production of ammonia
Hydrogenation of ethene
Fuel or fuel cells

Question 5

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)

Answer 5

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-

Question 6

Two advantages of vehicles using fuel cells

Answer 6

Less CO2 or less greenhouse gases produced

Greater efficiency

Question 7

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

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

Answer 7

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-

Question 8

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

Answer 8

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

Question 9

Reaction between ammonia and oxygen to make NO

Answer 9

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

Question 10

Two large scale uses for hydrogen

Answer 10

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

Question 11

What is d block element?

Answer 11

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

Question 12

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

Answer 12

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

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

Question 13

CO + 2H2 CH3COH

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

Answer 13

Equilibrium shifts to left

Question 14

suggest why methanol is added to petrol?

Answer 14

adds oxygen

Question 15

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

Answer 15

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

Question 16

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

Answer 16

• 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

Question 17

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

Answer 17

• 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

Question 18

What does value ok Ka tell you about an acid?

Answer 18

It’s strength

Question 19

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

Answer 19

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

Question 20

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?

Answer 20

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

Question 21

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

Answer 21

pH makes numbers more manageable/removes very small numbers

Question 22

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

Answer 22

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-

Question 23

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

Answer 23

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

Question 24

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

Answer 24

Adsorbed on a solid or stored as a liquid under pressure

Question 25

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

Answer 25

- Kc doesn't change with pressure - [NO2]^2 increases more than [N2O4] - equilibrium shifts to right so [N2O4] increases to maintain Kc

Question 26

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

Answer 26

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

Question 27

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

Answer 27

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

Question 28

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)

Answer 28

- 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

Question 29

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

Answer 29

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

Question 30

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

Answer 30

Same energy is spread over a larger volume | around 11