Blakhitman's chem questions thread!

[Blakhitman]

Totally forgot redox ><. I can do half equations for things like, Zn²⁺ to Zn. But don't know how to do these.

Write half equations to represent:
a   the reduction of SO₄^2– to SO₂
b   the oxidation of H₂O₂ to O₂
c   the reduction of MnO₄^– to MnO₂
d   the oxidation of SO₃^2– to SO₄^2–

Thanks!

[coletrain]

when you do questions like this i like to use KOHES to balance then
Balance the Key elements
Balance Oxygen by adding H20
Balance Hydrogen by adding H+ (H30+)
Balance the net charge by adding E lectrons
Add States

Eg Reduction of SO42- TO SO2
key elements are balanced
add H2O to balance oxygen
S042- = S02 +2H20
add H+
4H++SO42-= SO2+ 2H20
balance the net charge by adding electrons
2e- (4H+)+S042-=SO2+(2H2O)
then add that states

please feel free to correct me if im wrong

[Edmund]

Beaten But here's what I usually do:

1. Balance key elements such as Mn, S, Ca etc...

2. Balance oxygen by adding the appropriate number of H₂O to the correct side

3. Balance hydrogen by adding the appropriate number of H⁺

4. Count up the charges on each side and add the right number of e^- to balance charges

[Blakhitman]

Thanks a lot guys.

So would b) end up being ?

[Edmund]

Thanks a lot guys.

So would b) end up being ?

That's correct

[Blakhitman]

Oh excellent, thanks a heap!

[Blakhitman]

Balance the following redox equations by i) separating them into two half equations, balancing each equation, and then ii) combining the pair into a balanced complete redox equation.
a   H2O2 (aq) + PbS(s) --> PbSO4(s) + H2O(l)

ok this is what I did, is it correct?

i)

   

ii)

[Studyinghard]

Balance the following redox equations by i) separating them into two half equations, balancing each equation, and then ii) combining the pair into a balanced complete redox equation.
a   H2O2 (aq) + PbS(s) --> PbSO4(s) + H2O(l)

ok this is what I did, is it correct?

i)

  

ii)

yes except ii) should be

ii) PBS + 4H₂O₂ --> PbSO₄ + 4H₂O

That is because have H₂O on both sides is apparentally unprofessional. I dont think they can cancel marks for it but its just better to have it like that.

Someone can correct me if im wrong

[coletrain]

Balance the following redox equations by i) separating them into two half equations, balancing each equation, and then ii) combining the pair into a balanced complete redox equation.
a   H2O2 (aq) + PbS(s) --> PbSO4(s) + H2O(l)

ok this is what I did, is it correct?

i)

   

ii)

yes except ii) should be

ii) PBS + 4H₂O₂ --> PbSO₄ + 4H₂O[/tex]

That is because have H₂O on both sides is apparentally unprofessional. I dont think they can cancel marks for it but its just better to have it like that.

Someone can correct me if im wrong

yeah your right, just to make everything tidy

[Blakhitman]

Ok, so you subtracted left from right.

Thanks!

[Studyinghard]

Ok, so you subtracted left from right.

Thanks!

Yep, that should be done with any H⁺'s if there any left over on both sides.

[coletrain]

Ok, so you subtracted left from right.

Thanks!

Yep, that should be done with any H⁺'s if there any left over on both sides.

do you also do it if you have other common species eg H20 on either side?

[kyzoo]

Yep, it's just algebra.

[Studyinghard]

Ok, so you subtracted left from right.

Thanks!

Yep, that should be done with any H⁺'s if there any left over on both sides.

do you also do it if you have other common species eg H20 on either side?

What do you mean? as in for H20 - water.

Thats what I did up there ^^

ii) PBS + 4H2O2 --> PbSO4 + 4H2O. I cancelled the H20 from the left and kept it on the right.

[coletrain]

Ok, so you subtracted left from right.

Thanks!

Yep, that should be done with any H⁺'s if there any left over on both sides.

do you also do it if you have other common species eg H20 on either side?

What do you mean? as in for H20 - water.

Thats what I did up there ^^

ii) PBS + 4H2O2 --> PbSO4 + 4H2O. I cancelled the H20 from the left and kept it on the right.

yeah sorry didnt see that, dw your right