Simpl question about water, those damn water equations (1 Viewer)

[tau281290]

How do I know when do I use which??

H2O + e- --> 1/2H2(g) + OH-

1/2O2(g) + H2O + 2e- --> 2OH-

1/2O2(g) + 2H+ 2e- --> H2O



They are these 3 i am confused about.

I think the first one is cathode? thrid is anode? And what about the 2nd one?

tyty

 

[Zippora]

How do I know when do I use which??

H2O + e- --> 1/2H2(g) + OH-

1/2O2(g) + H2O + 2e- --> 2OH-

1/2O2(g) + 2H+ 2e- --> H2O



They are these 3 i am confused about.

I think the first one is cathode? thrid is anode? And what about the 2nd one?

tyty

the first one is cathode, because reduction is occuring

the second one occurs at the cathode of a corrosion reaction, however when the conditions of the corrosion are acidic, then the third reaction occurs

the last one is oxidation which occurs at the anode, and you write it in reverse

that is my understanding,

 

[tau281290]

I see, if its acidic corrosion, you use the third one...

 

[Zippora]

I see, if its acidic corrosion, you use the third one...

is that a sarcastic/confused statement, or an enlightened one?

 

[tau281290]

I am enlightened by u, but how come ive never read this in text books? Which part is this? do u know?

 

[Zippora]

i never really listened during the shipwrecks topic in class but ive been learning from the keep it simple science booklet and thats what it says there

apparently its the reason that acidity increases corrosion, because the third reaction (which happens when conditions are acidic) occurs more readily than the second one as you can deduce from their relative positions of the table of standard potentials

keep in mind with the third reaction that when it is being occuring at the cathode of acidic corrosion, then it is written as is...

however in normal redox reactions when it occurs as oxidation at the anode, it is written in reverse, because it is oxidation

 

[adosh]

I see, if its acidic corrosion, you use the third one...

what do we mean by acidic conditions????? does it mean the electrolyte is acidic or basic,,t hat is if it is a sodium hydroxide electrolyte we use teh 'basic' oxidation of water equation????????

 

[tau281290]

well i think its just acidic corrosion, it happens when sulfate reducing bacteria produce H+ ions.

Well, ask Zippora...