What forms around the cathode during electrochemical processes? (1 Viewer)

[.ben]

Thanks

 

[kazan]

The cathode is reduced, meaning that it gains electrons, depending on wether this is a galvanic or a electrolytic cell, this can be done in differnt ways, for galvanic cells, ions form on the cathode.

 

[243_robbo]

remeber RED CAT, so reduction occurs at teh cathode. This means that an ion is gaining electrons and depending on the ion in question may stay in solution but lower in oxidisation number, be reduced to a solid which forms on the cathode itself, or be reduce to a gas which floats away into oblivion. To detirmine what occurs you must analyse the potential candidates for reduction, generally these are either cations or the water itself. some cations like Na+ are never reduced in aqueous solution as water has a greater reduction potential. However some ions such as Cu+ will always be reduced with priority over water as they have a greater reduction potential. For ions witha similar reduction potential to water, they will only be reduced if they are in sufficient concentration.

O yeah and if you're not sure waht reduction potential is, it is simply a mreasure of what is more like ly to be reduced. The standard emf's for the reduction half cells found in your data sheet are reflections of these values. Being a standard REDUCTION table, the greatuer the emf number (further down the page), the more likely that particular ion/molecule is to be reduced. SO say youve got a solution containing sliver ions. look at the table, the reduction of silver ions to silver is waaay further down than the reduction of water, so they are reduced as a solid onto the cathode. HOwer take the example of calcium ions. In this case, water is below the Ca2+ reduction half equation so it takes priority, meaning that water is reduced to form hydrogen gas which bubbles out at the cathode. Howver if we take zinc ions for example, their half equation is right under water's. So they will be reduced only if their concentration is high enough (you dont need to know exactly how high).

hope that helped

 

[neverbee]

To REMEMBER WHAT REDUCTION AND OXIDATION ARE:

OIL RIG

O xidation
I s
L oss

R eduction
I s
G ain

Oxidation is loss of electrons..... Solid --> Ions
EG FE -> Fe2+ + 2e- (yay for shipwrecks)

Reduction is gain .... Ions gain electrons to become a "solid" (or more precicely atoms rather than ions) ...Ions -->solid

Also The terms are "in alphabetical order"



To REMEMBER WHICH ONE IS THE CATHODE .... -->


Anode is before Cathode in the alphabet as (A is before C, O is before R)
Oxidation is before Reduction in the alphabet
So:
Anode - Oxidation
Cathode - Reduction



To REMEMBER WHICH IS THE POSITIVE ION --->

(A is before C, N is before P)
ANion is a Negative Ion
CATion is a Positive ion

 

[.ben]

What so a galvanic cell with a salt bridge doesn't form anything cos the salt bridge allows migration of ions?

 

[kazan]

the salt bridge allows migration of ions so that it doesn't <b> fully</b> ionise. there will still be transfer of electrons, but the salt bridge allows some to return.

 

[Riviet]

The salt bridge also completes the circuit and maintains electrical neutrality in the cells.