chapter 23 Flashcards
what are tips in forming half equations?
balance electron numbers to add them together
make sure charges balance
can also use oxidation numbers
what is the manganate VII redox titrations experiement?
solution of MnO4- goes into burette
pipette measure volume of solution being analysed
dilute H2SO4 is added in excess
end point at PPP (pale pink persists)
why is manganate used for analysis of many different reducing agents?
because it is a very good oxidising agent
what is the iodine/thiosulfate redox titrations experiment?
excess potassium iodide added to oxidising agent
solution turns yellow-brown
mixture titrated with sodium thiosulfate
brown colour fades
close to end point appears straw yellow
add starch indicator to identify end point (when it turns blue black)
what is a voltaic cell?
allows oxidation and reduction equations to occur separately in half cells
electrons are transferred from one half cell to another
what is in an isolated half cell?
metal rod
solution with metal ions in it
no net transfer of electrons
what is in two half cells joined together?
voltmeter
salt bridge
metal rods
solutions with metal ions in (1 moldm-3)
what is the standard electrode potential?
the e.m.f of a half cell connected to a standard hydrogen half cell under standard conditions
what is electrode potential?
tendency to be reduced and gain electrons
what is in a standard hydrogen half cell?
platinum electrode
what do the electrode potential values show?
if at top of table (most negative) then are the best reducing agents (arrow goes backwards <—-)
if at bottom table (most positive) then are the best oxidising agents (arrow goes forwards —->)
what direction to electrons flow?
from negative electrode to positive electrode
what is the overall electrode potential of a cell?
electrode potential of positive electrode - electrode potential of negative electrode
what are the predictions that you can get from electrode potentials?
more negative electrode potential value half cells have a greater tendency to lose electrons
equilibrium moves left
what are the limitations of predicting electrode potential values?
activation energy may be very high so has very slow reaction time
electrode potential values apply to aqueous reactions
not standard conditions
what are primary cells?
non-rechargeable cells
cell reaction cannot be reversed
when chemicals are used up the voltage will fall and battery will go flat
what are secondary cells?
rechargeable cells
cell reaction is reversed during recharging process
what are fuel cells?
use energy from reaction of fuel with oxygen to create voltage
how do fuel cells work?
fuel and oxygen flow into cells
products flow out
electrolyte remains in cell
operates continuously (don’t need to recharge)
what do hydrogen fuel cells do?
release only water no CO2
