redox Flashcards
what is redox chemistry about?
electron transfer and the ability for electrons to be transferred
define oxidation
loss of electrons
define reduction
gain of electrons
define static electricity
electrons from either substance have been displaced
what are redox reactions?
the combination of reduction and oxidation in the hopes of electron transfer
the species that undergoes oxidation is…
the reductant
the species that undergoes reduction is…
the oxidant
trends in electronegativity. what substance is most electronegative?
increases left to right and down to up. fluorine is most electronegative
defin electronegativity
ability to attract electrons
define strong oxidant
really wants to under go reduction
define strong reductant
really wants to undergo oxidation
the transfer of electrons is?
simultaneous and spontaneous
what determines if a redox reaction will occur?
downhill gradient
what does a half cell do?
host a redox half reaction
what happens when two half cells are joined?
a full redox reaction can occur
describe a solid-aqueous half cell
- metal insert
- electrolyte contains the same metal in ion form
solid: electrode
aqueous: electrolyte
describe an aqueous-aqueous half cell. what is the electrode for?
- both aqueous
- inert electrode (solid) such as platinum or graphite is needed
electrode conducts the electrons
describe the aqueous-gaseous half cell
- inert electrode
- as gas (product or reactant) is involved there is a tube
what is the energy transformation of galvanic cells?
chemical to electrical energy (electricity- flow of electrons)
what was the Daniel cell experiment observations?
Zn2+/Zn and Cu2+/Cu
- CuSO4 (aq) electrolyte became pale in colour
- Cu (s) electrode was covered in a film of black solid
- Zn (s) decreased in mass
- reaction between Cu2+ and Zn (s)
what is a conductor?
allows passage if e-. metals are conductors
define dissociation
when ionic compounds break apart eg. form aqueous solution
what does a salt bridge do? what ions are used?
prevents flow of electrons stopping by preventing accumulation of charge and completing the circuit. ones that are always soluble- K+ and NH4+ and SNAPE
what occurs at the cathode? what is the polarity?
reduction. +
what occurs at the anode? polarity?
oxidation. - because this is where electrons are being shot out
what happens to concentration if the ion at the anode?
due to oxidation, the ion concentration increases making a positive charge which is balanced with the salt bridge
what happens to concentration of the ion at the cathode?
due to reduction, the ion concentration decreases making the electrolyte more negative. this is neutralised by the salt bride
define voltage
the push in electrons
how is electromagnetic force (emf) or E0 value calculated?
cathode reaction or reduction or higher - anode or oxidation or lower reaction
how does gradient link to voltage
greater gradient, greater voltage
what can the ECST be used to predict redox reactions in:
- chemicals used in industry
- transport of chemicals
- extraction of metals eg. mining
oxidation numbers do what in oxidation?
increase
oxidation numbers do what in reduction?
decrease
what is the oxidation number rule for free elements?
- solids, liquids, gases
- ox no of 0
- H2O and other free compounds have an ox no of 0 too
what is the oxidation number rule for ions
- the same as charge
what is the oxidation number rule for polyatomic ions? oxygen and hydrogen rules
calculate it using algebra for key elements (not oxygen or hydrogen)
oxygen: ox. no. is always -2 except in hydrogen peroxide (H2O2) where it is -1
hydrogen: always +1 except in metal hydrides (metal with hydrogen) such as NaH in which case it is -1. the is because hydrogen has an extra space to fill and will pick up an electron
balancing complex redox reactions rules
K- balance key elements O- balance oxygen with H2O H- balance hydrogen with H+ (protons) E- balance electrons S- add states
