Balancing Equations.

Chemistry discussion, revision, exam and homework help.

Announcements Posted on
Ask me ANYTHING - Andrew O'Neill - Buzzcocks comedian, amateur occultist, vegan... 22-05-2013
IMPORTANT: You must wait until midnight (morning exams)/4.30AM (afternoon exams) to discuss Edexcel exams and until 1pm/6pm the following day for STEP and IB exams. Please read before posting, including for rules for practical and oral exams. 28-04-2013
Sign in to Reply
  1. EffKayy's Avatar
    • TSR Demigod
    • Posts: 6,700
    Balancing Equations.
    (Original post by charco)
    x
    Quoted charco as he helped me last time regarding a markscheme situation.

    In a markscheme an answer to a balanced equation is:

    4NH3 + 302 --> 2N2 + 6H20

    However I put

    2NH3 + 1 1/2 02 --> N2 + 3H20

    Usually they say 'OR multiples' or something to that effect in the markscheme, however it doesnt say that here, neither is it in the reject column.

    Is this correct/incorrect?
  2. Plato's Trousers's Avatar
    • Community Assistant
    • PS Helper
    • Supreme Being
    • Location: London/Oxford Posts: ∞
    Re: Balancing Equations.
    (Original post by EffKayy)
    Quoted charco as he helped me last time regarding a markscheme situation.

    In a markscheme an answer to a balanced equation is:

    4NH3 + 302 --> 2N2 + 6H20

    However I put

    2NH3 + 1 1/2 02 --> N2 + 3H20

    Usually they say 'OR multiples' or something to that effect in the markscheme, however it doesnt say that here, neither is it in the reject column.

    Is this correct/incorrect?
    What you have written is not actually incorrect as you have the right proportions of each element/compound. But it is usually best to avoid ending up with fractions in your equation as mark schemes usually prefer whole numbers of things. So in your equation, if you just multiply through by 2 you get rid of the 1.5
  3. NutterFrutter's Avatar
    • Banned
    • Posts: 4,631
    Re: Balancing Equations.
    (Original post by EffKayy)
    Quoted charco as he helped me last time regarding a markscheme situation.

    In a markscheme an answer to a balanced equation is:

    4NH3 + 302 --> 2N2 + 6H20

    However I put

    2NH3 + 1 1/2 02 --> N2 + 3H20

    Usually they say 'OR multiples' or something to that effect in the markscheme, however it doesnt say that here, neither is it in the reject column.

    Is this correct/incorrect?
    It should be allowed unless the question stated to use integers. Also, it would have been better to write the 1 1/2 as 3/2. Anyway, I don't see why they would reject it, mark schemes don't contain every piece of information for the examiner.
  4. Plato's Trousers's Avatar
    • Community Assistant
    • PS Helper
    • Supreme Being
    • Location: London/Oxford Posts: ∞
    Re: Balancing Equations.
    (Original post by NutterFrutter)
    It should be allowed unless the question stated to use integers. Also, it would have been better to write the 1 1/2 as 3/2. Anyway, I don't see why they would reject it, mark schemes don't contain every piece of information for the examiner.
    I agree. They shouldn't mark it wrong.
Sign in to Reply
Share this discussion:  
Article updates
Moderators

We have a brilliant team of more than 60 volunteers looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

Reputation gems:
The Reputation gems seen here indicate how well reputed the user is, red gem indicate negative reputation and green indicates a good rep.
Post rating score:
These scores show if a post has been positively or negatively rated by our members.