Results are out! Find what you need...fast. Get quick advice or join the chat
Hey! Sign in to get help with your study questionsNew here? Join for free to post

Chemistry Redox equations help please.

Announcements Posted on
    • Thread Starter
    • 1 follower
    Offline

    ReputationRep:
    qestion below.


    i dont know why there is a picture of that man there, i cant get rid of it either.
    Attached Thumbnails
    Click image for larger version. 

Name:	fdfgs.jpg 
Views:	29 
Size:	3.1 KB 
ID:	145936  
    • 16 followers
    Offline

    ReputationRep:
    (Original post by ReTurd)
    Hello. im stuck on this question. [pics below]
    Following the method used in the example i get an answer that is wrong because the h2o molecules dont balance, i got: 4HBr + H2SO4 -----> 2Br2 + SO2 + ??H2O

    the final answer shows there only being 2 HBr and 1 Br2 molecules in the equation. the reason i doubled mine is because i followed the instuctions in the example, (third line on step 2) where is says to balance any atoms that change exidation number in your draft equation.


    So why have they decided to use different methods in the two examples? It doesnt make sense.. how do i know if i should or shouldnt do that balancing thing??


    Attachment 145928Attachment 145929
    Attachments are not valid!
    • 1 follower
    Offline

    ReputationRep:
    1) H2SO4 + 2e- + 2H+ --> SO2 + H2O
    2) 2Br- --> Br2 + 2e-

    Add them together to get:

    3) H2SO4 + 2HBr --> SO2 + H2O + Br2
    • Thread Starter
    • 1 follower
    Offline

    ReputationRep:
    (Original post by arvin_infinity)
    Attachments are not valid!
    sorry, i think i got it working now
    • Thread Starter
    • 1 follower
    Offline

    ReputationRep:
    Hello. im stuck on this question. [pics below]
    Following the method used in the example i get an answer that is wrong because the h2o molecules dont balance, i got: 4HBr + H2SO4 -----> 2Br2 + SO2 + ??H2O

    the final answer shows there only being 2 HBr and 1 Br2 molecules in the equation. the reason i doubled mine is because i followed the instuctions in the example, (third line on step 2) where is says to balance any atoms that change exidation number in your draft

    So why have they decided to use different methods in the two examples? It doesnt make sense.. how do i know if i should or shouldnt do that balancing thing?

    Click image for larger version. 

Name:	2012-05-05 18.12.57.jpg 
Views:	84 
Size:	516.0 KB 
ID:	145950
    Click image for larger version. 

Name:	2012-05-05 18.13.28.jpg 
Views:	74 
Size:	501.4 KB 
ID:	145951
    • 2 followers
    Offline

    ReputationRep:
    Why don't you just put a 2 in front of HBr and a 2 in front of H2O, correct me if I am wrong but that is balanced...
    • 48 followers
    Offline

    ReputationRep:
    I can't see your images

    • Thread Starter
    • 1 follower
    Offline

    ReputationRep:
    Hello. im stuck on this question. [pics below]
    Following the method used in the example i get an answer that is wrong because the h2o molecules dont balance, i got: 4HBr + H2SO4 -----> 2Br2 + SO2 + ??H2O

    the final answer shows there only being 2 HBr and 1 Br2 molecules in the equation. the reason i doubled mine is because i followed the instuctions in the example, (third line on step 2) where is says to balance any atoms that change exidation number in your draft

    So why have they decided to use different methods in the two examples? It doesnt make sense.. how do i know if i should or shouldnt do that balancing thing?

    Click image for larger version. 

Name:	2012-05-05 18.12.57.jpg 
Views:	84 
Size:	516.0 KB 
ID:	145950
    Click image for larger version. 

Name:	2012-05-05 18.13.28.jpg 
Views:	74 
Size:	501.4 KB 
ID:	145951
    • Thread Starter
    • 1 follower
    Offline

    ReputationRep:
    (Original post by EierVonSatan)
    I can't see your images

    i think i have it fixed now ^^ in the post above. thanks
    • 48 followers
    Offline

    ReputationRep:
    (Original post by ReTurd)
    i think i have it fixed now ^^ in the post above. thanks
    Cools :yy: I'll just go through the question with the example method they've outlined (there are lots of methods to balance equations, you might find another easier).

    Step 1: Write down what you're told

    HBr + H2SO4 ---> Br2 + SO2

    Step 2: oxidation changes

    You are told to balance any atom that changes oxidation number so:

    2HBr + H2SO4 ---> Br2 + SO2 (now S and Br are balanced, but H and O are not)

    now compare the oxidation states

    2HBr + H2SO4 ---> Br2 + SO2

    Sulfur has gone from +6 to +4 (reduction = -2)

    2HBr + H2SO4 ---> Br2 + SO2

    bromine has gone from 2 x -1 to 2 x 0 (oxidation = +2)

    Step 3: Balance oxidation changes

    Nice and easy this time, they already balance

    Step 4: Clean up

    2HBr + H2SO4 ---> Br2 + SO2

    two extra oxygens on the left, 4 extra hydrogens - add two waters to the right

    2HBr + H2SO4 ---> Br2 + SO2 + 2H2O

    That help?
    • 1 follower
    Offline

    ReputationRep:
    why neg
    • Thread Starter
    • 1 follower
    Offline

    ReputationRep:
    (Original post by EierVonSatan)
    Cools :yy: I'll just go through the question with the example method they've outlined (there are lots of methods to balance equations, you might find another easier).

    Step 1: Write down what you're told

    HBr + H2SO4 ---> Br2 + SO2

    Step 2: oxidation changes

    You are told to balance any atom that changes oxidation number so:

    2HBr + H2SO4 ---> Br2 + SO2 (now S and Br are balanced, but H and O are not)

    now compare the oxidation states

    2HBr + H2SO4 ---> Br2 + SO2

    Sulfur has gone from +6 to +4 (reduction = -2)

    2HBr + H2SO4 ---> Br2 + SO2

    bromine has gone from 2 x -1 to 2 x 0 (oxidation = +2)

    Step 3: Balance oxidation changes

    Nice and easy this time, they already balance

    Step 4: Clean up

    2HBr + H2SO4 ---> Br2 + SO2

    two extra oxygens on the left, 4 extra hydrogens - add two waters to the right

    2HBr + H2SO4 ---> Br2 + SO2 + 2H2O

    That help?
    i can see what you have done there, but aren't you supposed to ignore the coefficient/number in front of the molecule when assigning oxidation numbers (this is why my answer is different and why i ended up getting an oxidation number of only -1 and ended up doubling it.

    e.g. 2H2SO4 and H2SO4
    Each H has an oxidation number of +1 in both, and the same with the other atoms. So in the 2H2SO4 molecule you cant say the the oxidation number of H is 2 x +1 = +2

    does that make sense, am i right, wrong?
    • 48 followers
    Offline

    ReputationRep:
    (Original post by ReTurd)
    i can see what you have done there, but aren't you supposed to ignore the coefficient/number in front of the molecule when assigning oxidation numbers (this is why my answer is different and why i ended up getting an oxidation number of only -1 and ended up doubling it.

    e.g. 2H2SO4 and H2SO4
    Each H has an oxidation number of +1 in both, and the same with the other atoms. So in the 2H2SO4 molecule you cant say the the oxidation number of H is 2 x +1 = +2
    It's quite subtle. It's not saying the oxidation number is +2 for hydrogen just that there are 2 hydrogens of oxidation state +1.

    In the example above, it's saying that the overall oxidation change over the reaction has increased by +2 not that the individual oxidation state of each bromide is -2 on the left. In other words you need to lose 2 electrons to oxidise 2 bromide atoms - one for each bromide in the reaction.

    These overall quantities in brackets is the bit relating to step 3.

Reply

Submit reply

Register

Thanks for posting! You just need to create an account in order to submit the post
  1. this can't be left blank
    that username has been taken, please choose another Forgotten your password?
  2. this can't be left blank
    this email is already registered. Forgotten your password?
  3. this can't be left blank

    6 characters or longer with both numbers and letters is safer

  4. this can't be left empty
    your full birthday is required
  1. By joining you agree to our Ts and Cs, privacy policy and site rules

  2. Slide to join now Processing…

Updated: May 5, 2012
New on TSR

GCSE mocks revision

Talk study tips this weekend

Article updates
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.