Redox reactions, chemical cells and electrolysis
chemical cells
cannot be recharged
primary cells
alkaline manganese cells
silver oxide cells
zinc-carbon cells
can be recharged
secondary cells
nickel-metal hydride cells
lithium ion cells
lead-acid accumulator
metal couples and electrolyte
called
electrolyte
soluble ionic cpd in water
mobile ions
chemical cell
2 different metal electrode
negative electrode (more reactive)
greater tendency to lose electrons
positive electrode (less reactive)
electrons flows from the negative electrode to the positive electrode through the external circuit
voltage of a chemical cell
can be measured by
multimeter
electrochemical series
metal X (negative electrode) + copper (positive electrode)
connected to multimeter
+ve value
-ve value
electrons flows from metal X to Cu
metal X is more reactive than Cu
electron flows from Cu to metal X
Cu is more reactive than metal X
Cu loses electron more readily than metal X
metal X loses electron more readily than Cu
metal X has a higher position than Cu in ECS
Cu has a higher position than metal X in the ECS
K, Ca, Na, Mg, Al, Zn, Fe, Pb, H2, Cu, Ag, Au
higher pos = greater tendency to lose electrons
different reactivity
two half cells
salt bridge
completes the circuit
provides ions to balance the charge
two half cells
porous device
allowing ions to move from one half cell into another
prevents direct mixing of the two electrolytes
allows ions to move from one electrolyte into another
different tendency/ readiness to lose electrons
Redox reaction
reduction
oxidation
oxidizing agent
reducing agent
自己做Reduction 令對手做Oxidation
自己做oxidation 令對手做reduction
loses electrons
gains electrons
Red Cat (reduction in cathode)
An Ox (oxidation in anode)
oxidation number
imgainary charge of the ion
rules of oxidation number
oxdiation number of an element = 0
the oxidation number of an element in a simple ion is equal to the charge on the ion
oxidation number of some element is fixed
all Grp 1 metals in its cpd, ON = +1
all Grp 2 metals in its cpd, ON = +2
Hydrogen in most of its cpd, ON = +1
fluorine in all of its cpd, ON = -1
chlorine, bromine, iodine in most of its cpd, ON=-1
oxygen in most of its cpd, ON=-2
the sum of oxidation number of all elements
in polyatomic ion
equals to the charge on the ion
in a compound
equals to zero
oxidation number of an element may vary from compound to compound
The oxidation number of (element) in (cpd)
= __
must with + -
eg, +1, -2,+3, -4
ON increase
ON decrease
Reducing power 由上而下 decrease
Oxidizing power 由下而上 decrease