past paper qs Flashcards
Typical reactions of transition metals and examples
1. Ligand substitution [Co(H2O)6]2+ + 4Cl- [CoCl4]2- + 6H2O pink ---------------------> blue - beige on standing 2. Precipitation Cu2+ + 2OH- --> Cu(OH)2 blue ---------------> blue precipitate 3. Redox MnO4- + 5Fe2+ + 8H+ ---> Mn2+ + 4H2O + 5Fe3+ purple ---------------------> clear/pink
The enthalpy and entropy changes of a reaction both have a negative sign. Discuss how the feasibility of this reaction will change as the temperature increases
reaction becomes less feasible because T∆S becomes more negative/increases in magnitude, so ∆G becomes less negative.
What happens if a small amount of ammonia is added to aqueous copper ions? and an excess?
small amount: Cu(OH)2 blue precipitate forms
large amount:
[Cu(H2O)6]2+ + 4NH3 –> [Cu(H2O)2(NH3)4]2+ + 4H2O
What happens if a small amount of ammonia is added to aqueous cobalt ions? and an excess?
small amount: green precipitate Co(OH)2
excess:
[Co(H2O)6]2+ + 6NH3 –> [Cu(NH3)6]2+ +6H2O
pink —————————> beige§
Explain the biochemical importance of iron in haemoglobin , including ligand substitution.
Haemoglobin contains 4 prosthetic harm groups. Each harm group has an Fe2+ at its centre - oxygen can bind to the Fe2+ ion, allowing it to be carried around the body.
It is dropped off at respiring tissues because CO2 has a higher stability constant than O2 so replaces is in a ligand substitution reaction.
Explain the following:
when water melts or boils, ∆H is positive and ∆S increases.
+∆H because intermolecular forces broken.
∆S increases because particles are more disordered in a gas than in liquid or solid.
How is the choice of an indicator linked to the titration curve?
pH range of indicator must match the vertical section of the graph / endpoint of indicator matches rapid pH change
Outline a series of experiments that could be carried out using the initial rates method to determine the orders of 2 reactants, A and B?
Vary [A], keeping [B] constant, and measure time taken for the reaction to happen.
Repeat varying [B], keeping [A] constant.
Obtaining rate from time:
Initial rate is proportional to 1/t
Plot a graph of initial rate against initial conc.:
Interpretation:
horizontal line = 0 order
straight line through origin = 1st order
exponential/half parabola = 2nd order
State one important difference between a fuel cell and a conventional storage cell
A fuel cell reacts a fuel such as H2 with oxygen to produce a voltage/electrical energy.
What are 2 d-block elements that have atoms with no unpaired d electrons?
Ti and Ni
Electronic configuration of chromium
1s2 2s2 2p6 3s2 3p6 4s1 3d5
One electron in each orbital in 4s and 3d orbitals, no orbitals completely filled
Electronic configuration of copper
1s2 2s2 2p6 3s2 3p6 4s1 3d10
3d fills befor 4s
What is Kstab?
the equilibrium constant for an equilibrium existing between a transition metal ion surrounded by water ligands and the complex formed when the same ion has undergone a ligand substitution. Water left out as in large excess so virtually constant.
[substituted complex]/[original complex][new ligands]
Suggest 2 advantages of using methanoic acid as the fuel in a fuel cell rather than hydrogen?
- methanol acid is a liquid and easier to store (not under pressure like H2)
- hydrogen is explosive/more flammable
- HCOOH gives a greater cell potential
- more public/political acceptance as a fuel
Explain, in terms of their electrode potentials (Cr = -0.74, Cu = +0.34) why chromium is more reactive than copper in their reaction
Electrode potential for chromium system is more negative than copper redox system.
Chromium system shifts left (loses electrons more readily, stronger reducing agent)
Copper system shifts right (loses electrons less readily, weaker reducing agent)
