EEE past paper questions Flashcards
Equation for reaction when ammonia is heated with oxygen to form NO
4NH3 + 5O2 –> 4NO + 6H2O
How to determine initial rate of reaction using graph
Tangent at t = 0
What is bronsted-lowry acid?
A proton donor
Large scale uses for hydrogen
Production of ammonia
Hydrogenation of ethene
Fuel or fuel cells
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)
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-
Two advantages of vehicles using fuel cells
Less CO2 or less greenhouse gases produced
Greater efficiency
3MnO4 2- + 2H2O 2MnO4 - + MnO2 + 4OH-
how can equilibrium position be shifted by bubbling CO2 gas through the mixture?
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-
Explain why enthalpy change of hydration of magnesium ions is more exothermic than for calcium ions
Magnesium ions have greater charge density because they are smaller ions
Thus, the have stronger bonding with H2O because greater electrostatic attraction
Reaction between ammonia and oxygen to make NO
2NH3 + 2.5O2 -> 2NO + 3H2O
Two large scale uses for hydrogen
Production of ammonia, hydrogenation of ethene, fuel or fuel cells
What is d block element?
elements who’s highest energy sub shell is a d-sub shell
KOH electrolyte decomposes forming H2 at one electrode and O2 at the other, predict the half equations
4OH- -> O2 + 2H2O + 4e-
2H2O + 2e- -> H2 + 2OH-
CO + 2H2 CH3COH
Temp increased, pressure constant, Kc decreased, what happened to equilibrium?
Equilibrium shifts to left
suggest why methanol is added to petrol?
adds oxygen
1st electron affinity of oxygen is negative, second is positive. Why is second positive?
Oxide ion and electron are both negative, so energy is required to overcome the repulsion
Describe with examples, equation and observations, the reaction transition metals undergo
- 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
Describe the different shapes and stereoisomers shown by complex ions with examples
- 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
What does value ok Ka tell you about an acid?
It’s strength
How do you choose an acid to make a buffer with if you have pKa values ?
Choose an acid with a pKa value closest to the target pH
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?
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
Advantages of using the pH scale to measure conc. of H+ in acid
pH makes numbers more manageable/removes very small numbers
Why is it difficult to predict whether lattice enthalpy of magnesium sulphide would be more or less exothermic than LE of sodium oxide [4]
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-
Why is it difficult to determine the lattice enthalpy of Na2CO3 using a born haber cycle?
Carbonate ion contains C and O, cycle needs formation of CO32- from C and O
Methods being developed to store hydrogen for possible use as a fuel in cars
Adsorbed on a solid or stored as a liquid under pressure
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
- Kc doesn’t change with pressure
- [NO2]^2 increases more than [N2O4]
- equilibrium shifts to right so [N2O4] increases to maintain Kc
Explain the term standard electrode potential as applied to the reduction of aqueous halogens
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
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
Lithium is highly reducing because it has a highly negative standard electrode potential.
2Li (s) + 2H2O –> H2(g) + 2LiOH
H2 gas is highly flammable
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 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
Explain in terms of Kc why equilibrium yield of C increases when pressure is increased:
Kc = [C]^2/[A][B]^3
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
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
Same energy is spread over a larger volume
around 11
