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# erm is this the correct half equation for oxygen? search engines wont tell me :( watch

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1. for magnesium it's: Mg(2+) + 2e- -> Mg

(assume O_2 means oxygen molecule)

is the half equation for oxygen: 1/2O_2 (2-) + 2e- -> O

?

thanks a lot!
2. This is for when magnesium burns to produce magnesium oxide
3. For the reaction Mg(s) + ½O2(g) ---> MgO

then ½O2 + 2e- ---> O2-
4. (Original post by dumb maths student)
for magnesium it's: Mg(2+) + 2e- -> Mg

(assume O_2 means oxygen molecule)

is the half equation for oxygen: 1/2O_2 (2-) + 2e- -> O

?

thanks a lot!
If it was this 1/2O_2 (2-) + 2e- then you'd get this 1/2O_2(4-)

It would be 1/2O_2 (2-) -> O + 2e-
5. (Original post by EierVonSatan)
For the reaction Mg(s) + ½O2(g) ---> MgO

then ½O2 + 2e- ---> O2-
ahh ok im confused.

1/2O2 has oxidising state -2 right? so adding 2 electrons would reduce it to -4?

why do u add 2 electrons to the equation? aren't u trying to stabalise it? so you take away 2 electrons instead?
6. (Original post by dumb maths student)
ahh ok im confused.

1/2O2 has oxidising state -2 right? so adding 2 electrons would reduce it to -4?

why do u add 2 electrons to the equation? aren't u trying to stabalise it? so you take away 2 electrons instead?
Elements have an oxidation state of zero. O2 accepts electrons from magnesium to form the O2- ion.
7. (Original post by gingergooner)
If it was this 1/2O_2 (2-) + 2e- then you'd get this 1/2O_2(4-)

It would be 1/2O_2 (2-) -> O + 2e-
yeah that actually does make sense.. but i'm not sure which is correct, urs or the above poster's

8. (Original post by dumb maths student)
for magnesium it's: Mg(2+) + 2e- -> Mg

(assume O_2 means oxygen molecule)

is the half equation for oxygen: 1/2O_2 (2-) + 2e- -> O

?

thanks a lot!
If you already know that the first half equation is
Mg(2+) + 2e- -> Mg
Then to balance it out, the other one would be
1/2O_2(2-) -> O + 2e-
Thus making the full equation
Mg(2+) + 1/2O_2(2-) -> MgO
9. (Original post by EierVonSatan)
Elements have an oxidation state of zero. O2 accepts electrons from magnesium to form the O2- ion.
oh i see, but then doesnt that mean MgO2 has a 2- oxidising state?

i thought that if Mg loses 2 electrons oxygen would gain 2, so both atoms are stable?
10. (Original post by dumb maths student)
oh i see, but then doesnt that mean MgO2 has a 2- oxidising state?
That species doesn't exist

I thought that if Mg loses 2 electrons oxygen would gain 2, so both atoms are stable?
You thought right!

Mg ---> Mg2+ + 2e- (magnesium donates two electrons)

½O2 + 2e- ---> O2- (oxygen accepts two electrons)
11. (Original post by dumb maths student)
oh i see, but then doesnt that mean MgO2 has a 2- oxidising state?

i thought that if Mg loses 2 electrons oxygen would gain 2, so both atoms are stable?
How did you know the first half equation? Did you work it out yourself or was it given?
12. (Original post by gingergooner)
How did you know the first half equation? Did you work it out yourself or was it given?
both were given but i suspected that the oxygen equation was wrong because i understood everything up to there.

i was wrong
13. (Original post by EierVonSatan)
You thought right!

Mg ---> Mg2+ + 2e- (magnesium donates two electrons)

½O2 + 2e- ---> O2- (oxygen accepts two electrons)
lol sorry, but if magnesium has a positive oxidising state, shouldn't it be the one ACCEPTING the electrons? in order to be stable.

did u get them mixed up or am i being stupid >_<
14. (Original post by dumb maths student)
lol sorry, but if magnesium has a positive oxidising state, shouldn't it be the one ACCEPTING the electrons? in order to be stable.
Solid magnesium is an element and has an oxidation state of zero. Metals lose electrons to form ions, in this case Mg2+.

It might just be because they're written as reductions (by convention) that you might be getting confused?
15. (Original post by dumb maths student)
both were given but i suspected that the oxygen equation was wrong because i understood everything up to there.

i was wrong
Because its an ionic compound EierVonSatan should be right, magnesium with a 2+ charge is attracted to oxygen with a 2- charge, and as they are bonded the overall compound is neutral.
Edit: neutral and therefore stable
16. (Original post by EierVonSatan)
Solid magnesium is an element and has an oxidation state of zero. Metals lose electrons to form ions, in this case Mg2+.

It might just be because they're written as reductions (by convention) that you might be getting confused?
ah snap!

i understand now, thanks a lot man
17. (Original post by gingergooner)
Because its an ionic compound EierVonSatan should be right, magnesium with a 2+ charge is attracted to oxygen with a 2- charge, and as they are bonded the overall compound is neutral.
Edit: neutral and therefore stable
i understand now

thanks for the help much appreciated

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