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Chemistry: Post your doubts here!

Discussion in 'International A And AS Level' started by XPFMember, Sep 29, 2011.

  1. Hamnah Zahoor

    Hamnah Zahoor

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    Answer is C....
     
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  3. Tigercub

    Tigercub

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    coniine is the major constituent of the poison ‘oil of hemlock’
    Connine can be synthesised by reacting ammonia with a dibromo compound, X
    Q28
    9701/12/mj/12
    What is the name of compound ?
    A 1,1-dibromo-2-propylcyclopentane
    B 1,2-dibromo-2-propylcyclopentane
    C 1,4-dibromooctane
    D 1,5-dibromooctane
    pls help ;/
     
  4. Tigercub

    Tigercub

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    In the manufacture of sulfuric acid the reaction 2SO2(g) + O2(g) 2SO3(g) usually takes place at 400 °C and 1 atm pressure. In one industrial plant, it is decided to change the pressure to
    20 atm

    What will be the consequences of this change
    1 increased running costs
    2 an increased percentage of sulfur trioxide in the equilibrium mixture
    3 the rate of the backward reaction increases

    The answer is A which 1,2 and 3 are correct
    But how the rate of the backward reaction increases? I thought it should be decreases?
     
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  5. razor8771

    razor8771

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    Q-Use of the Data Booklet is relevant to this question. Which sodium compound contains 74.2% by mass of sodium?
    A sodium carbonate
    B sodium chloride
    C sodium hydroxide
    D sodium oxide

    Anyone?? Answer is D but I can't figure out why :/
     
  6. Hamnah Zahoor

    Hamnah Zahoor

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    (23*2)/((23*2)+16)*100=74.2%
    In sodium oxide formula is Na2O
     
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  7. razor8771

    razor8771

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    Ohh i understood, tysm
     
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  8. MShaheerUddin

    MShaheerUddin

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    X is a salt of one of the halogens chlorine, bromine, iodine, or astatine (proton number 85).
    The reaction scheme shows a series of reactions using a solution of X as the starting reagent.

    X HNO3/ AgNO3 a precipitate excess NH3(aq) colorless solution

    excess HNO3

    precipiate



    What could X be?

    A sodium chloride
    B sodium bromide
    C potassium iodide
    D potassium astatide
     
  9. Hamnah Zahoor

    Hamnah Zahoor

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    When x is added to silver nitrate a precipitate is formed which then dissolves in excess ammonia this dissolving shows that it will be a soluble halogen ....which means chloride. This is the main thing to be focused ...on reading the last step you might get confused but in excess of HNO3 it is actually the ammonia in the complex solution of Silver chloride that reacts to form ammonium nitrate and Silver chloride is left as precipitate.
     
    Last edited: Mar 3, 2018
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  10. Hinafatima

    Hinafatima

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    Kindly solve these
    May June 2017/11 q#20,24
     
  11. Hamnah Zahoor

    Hamnah Zahoor

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    For question 24

    acid catalyst is added when dehydration is being done ....considering the diagram divide it into two parts from the upper oxygen to the lower right branch and similar division on the left side and then draw the structural formula for it will match the compound in part C.:)
     
    Last edited: Mar 3, 2018
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  12. Hinafatima

    Hinafatima

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    got it thanks :)
     
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  13. Hinafatima

    Hinafatima

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    Thanks, got it, any idea of question 20?
     
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  14. Hamnah Zahoor

    Hamnah Zahoor

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    This is from the examination report
    Question 20
    The most commonly chosen incorrect answer was C. C, pentan-3-one, would be reduced to pentan-3-ol. This will dehydrate to give cis and trans pent-2-ene; two isomers. B, butanone, would be reduced to butan-2-ol. This will dehydrate to give cis and trans but-2-ene and but-1-ene, three isomers.

    Apart from above statement you have to focus on the statement ....Generating one product or mixture of products in case of option A one product is produced, in option B the product produced shows cis-trans isomerism which are in total three thus producing the most isomers..... same goes for the rest of the options.
     
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  15. Hinafatima

    Hinafatima

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    JazakAllah Khairan kaseera
    Actually i didn't have the examiner report so couldn't get any clue,thanks once again
     
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  16. Hamnah Zahoor

    Hamnah Zahoor

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    My pleasure:):).
     
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  17. feliciablack2000

    feliciablack2000

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    Dinitrogen tetroxide dissociates into nitrogen dioxide on heating.
    N2O4⇌2NO2
    In an experiment the partial pressures of the gases at equilibrium were found to be NO2 , 0.33 atm; N2O4, 0.67 atm
    What is the numerical value of Kp at the temperature of the experiment?
    A 0.16
    B 0.49
    C 0.65
    D 2.03
    If anyone is generous enough to help me solve this question, i would really appreciate it! :)
     
  18. Hamnah Zahoor

    Hamnah Zahoor

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    Kp=(0.33)^2/0.67=0.16 .....option A
     
  19. feliciablack2000

    feliciablack2000

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    Thankyou so much!
     
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  20. Holmes

    Holmes

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    Guys If anyone is struggling with the ORGANIC CHEMISTRY and other topics as well. Try the link below it's very useful. I got A grade just because of the notes provided on this website.
    http://www.khizarchemistry.com/book.html
     
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  21. mehran46

    mehran46

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    Hi there I am new to this site. Still trying to get familiar with it.
    Wanted the reason for the answer of question 9
    thanks
     

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