redox. Flashcards
what colour is the [Co(H2O)6]2+ ion
pink (octahedral)
what colour is the [CoCl4]2- ion
blue
what would the color change be in this reaction Co(H2O)6 2+ + 4Cl⇌ CoCl4 2- + 6H2O
pink to blue
what are the metals present in brass?
- copper
- zinc
give one common purpose for brass and state the property of brass which makes it ideal for that purpose
- musical instrument -> bc shiny + attractive.
- coins -> non rusting
what happens when a rod of metal is dipped into a solution of its own emails.
an equilibrium is set up between the solid metal and the aq metal ions
what is a standard Hydrogen half cell made of (3)
HCl acid of 1mol dm3
Hydrogen gas at 100kPa
inert platinum electrode.
why is hydrogen half cell used as a standard half cell.
its easy to control its purity and reproducibility.
how can u make a simple salt bridge/
- soak a piece of filter paper in (aq) solution of KNO3 or NH4NO3
why are salt bridges necessary?
- they complete the circuit by connectint the 2 solutions –> they allow flow of ions and thus charge is transferred between the half cells.
THEY DONT REACT W./ ELECTRODES>
why might u use other standard electrodes occasionally
- platinum is EXPENSIVE
- they might be CHEAPER, easier and quicker to use and can provide just as good reference.
if a E value is more negative what does it mean in terms of oxidising or reducing power?
- it is better reducing agent
- easy to oxidise.
if a E value is more positive or more positive, what does it mean in terms of oxidising or reducing power?
- better oxidising agent (easier to reduce)
how do u calculate the emf of a cell from E values
E cell = E pos - Eneg
when would u use a pt electrode when trying to work out the E cell?
- when both the oxidised and reduced forms of the metal are in aqueous solution.
HOW would u predict if an reaction will occur?
- take 2 half cell equations
- find the species being reduced.
- calculate the E value minus the E value of the species being oxidised
- if the overall E is >)>4V. a reaction will occur.
what are 3 main types of electrochemical cells.
- non rechargeable
- rechargeable cells
- fuel cells.
how do non rechargeable cells work? (primary cells)
the non reversible reaction provides energy until ALL reactants run out.
describe how rechargeable cells work. ( secondary cells)
- the reaction is non reversible
- when recharging the reactions of the cells can be reversed.
give some examples of rechargeable cells.
- Nickel and Cadmium batteries
- Lithium ion batteries + Lithium polymer batteries
- Lead acid batteries.
what is the use of lead acid batteries
- car batteries
what is the use of Nickel Cadmium batteries
- cylindrical batteries used in radios + torches etc
what are the uses of lithium ion + lithium polymer batteries
- modern appliances eg laptops and cameras.
explain why lithium is used in laptop batteries.
Lithium has low density so the electrode is light and v v reactive.
What are the drawbacks of using lithium batteries?
- they are toxic if ingested.
- rapid discharge of current can cause fire or even explosions
what is the fuel cell reaction at the cathode of alkali fuel cell
2H2O + 4e + O2 –> 4OH
what is the half cell equation at the anode of the alkali fuel cell
2H2+4OH –> 4h2O + 4e
what is the half cell equation at the cathode of an acid fuel cell.
1/2O2+ 2H+ + 2e —> H2O
what is the half cell equation at the anode of an acid half cell.
H2 —> 2h+ + 2e
