14.2 Flashcards
what is a storage cell/secondary cell
a cell that can be recharged by passing a current through it in the opposite direction to the flow of current generated by the cell
what are the disadvantages of nickel-cadmium
cadmium is very toxic therefor a lot of care needs to be taken when disposing of them
what is a fuel cell
produces a voltage from the chemical reaction of a fuel with oxygen
in a hydrogen-oxygen fuel cell what are the electrodes coated in and why
platinum as it acts as a catalyst
what are the advantages of a hydrogen-oxygen fuel cell
- offer an alternative to fossil fuels
- the reaction does not produce pollutants
- lighter and more efficient than fossil fuels
what are the disadvantages of a hydrogen-oxygen fuel cell
- hydrogen is explosive which makes compressing and transporting it very hazardous
- many metals absorb hydrogen
- hydrogen is usually supplied from methane which is a finite resource
why is potassium manganate(VII) used in redox reactions
it is a strong oxidising agent
what does potassium manganate(VII) form in alkaline solution
manganese(IV) oxide
brown precipitate
why is potassium manganate(VII) almost always used in acidic solutions
as in alkaline solutions it form manganese(VI) oxide which interferes with the end point colour
how does potassium manganate(VII) act as its own indicator
it will form manganese(II) ions which forms a colourless solution but as soon as the potassium manganese(VII) is in excess the solution will go pink
what colour are Fe^2+ ions
pale green
what colour are Fe^3+ ions
yellow
what colour are Mn^2+ ions
pale pink
what indicator is used for the titration of iodine with sodium thiosulfate
starch solution
why is the titration of potassium manganate (VII) and ethanedioic acid originally pink
because the reaction is very slow therefor must be heated to 60C and will begin pale pink then go colourless before going pink when excess potassium manganate (VII) is added
