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Chemistry: Post your doubts here!

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

  1. kuetian

    kuetian

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    Hydroxyethanal, HOCH2CHO, is heated under reflux with an excess of acidified potassium
    dichromate(VI) until no further oxidation takes place.
    What is the skeletal formula of the organic product?
     
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  3. kuetian

    kuetian

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    ans:a,b,c
     
  4. Hamnah Zahoor

    Hamnah Zahoor

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    This question is a bit confusing one :)
    From the examination report
    Question 35: The correct answer was A. The most commonly chosen incorrect answer was B. This suggests that for most candidates their choice of answer rested on the truth or otherwise of choice 3. If the operating pressure is increased for a process in which all reactants and products are gases then both the rate of the forward reaction and the rate of the backward reaction will increase, although by different amounts.
     
  5. Haroon Ahmed

    Haroon Ahmed

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    Can anyone kindly answer the question below(and explain why he/she chose the staement).
    Q.Two bulbs R and S, connected by a mercury manometer, are held in a thermostat, as shown. The volume of R is twice that of S. R contains gas, X, at the same pressure as the nitrogen in S.When the temperature is increased, which gases in bulb R would cause the mercury level in the right-hand limb of the manometer to rise? 1. an equilibrium mixture N2F4(g) to 2NF2(g); ∆H positive. (PAST PAPER REFERENCE;M-J/2007/PAPER 1/Q34.)
     
  6. Hamnah Zahoor

    Hamnah Zahoor

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    Answer is B....first draw the skeletal formula of HOCH2COH heating it under reflux will result in OH on both sides being oxidised to Acid i.e CO2H on both sides in option b There are two carbons with acis groups on each side.In option A there are three carbons while in option C and D no acid formed is shown.
     
  7. Hamnah Zahoor

    Hamnah Zahoor

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    Same groups or atoms on the opposite side of the double bond having same elctronegativites tends to cancel out the effect of each other thus reducing the overall dipole to a great extent.
     
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  8. Hamnah Zahoor

    Hamnah Zahoor

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    I guess here the question is focusing on the number of moles.... Considering that there is one mole of Nitrogen in bulb S than according to this in case where temperature is low equilibrium in reaction 1 will also have one number of moles for reverse reaction is being favoured but when temperature is being increased it will result in forward reaction being favoured and the number of moles of gas being produced increasing thus large number of moles of gas causes the mercury on left hand side to decrease due to increased pressure and right hand side to increase for the number of moles in s are low.For the rest of the options in both cases one mole is being produced thus having no effect on the mercury level.
     
  9. mushu.jr

    mushu.jr

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    1 Most submarines travel under water using electrical power from batteries. The German
    engineer Helmut Walter designed a diesel engine that could be used to propel a submarine
    beneath the surface of the sea. Instead of taking air from above the surface of the sea,
    Walter’s engine used hydrogen peroxide, H2O2, to provide oxygen for a conventional diesel
    engine.
    Hydrogen peroxide may be catalytically decomposed to give water and oxygen.
    (a) (i) What is meant by the term catalyst?
    ..................................................................................................................................
    ..................................................................................................................................
    (ii) Construct a balanced equation for the decomposition of H2O2.
    ............................................................................................................................. [3]
    Diesel fuel may be considered to consist of the hydrocarbon C15H32 which reacts completely
    with oxygen according to the following equation.
    C15H32 + 23O2 → 15CO2 + 16H2O
    (b) (i) To which homologous series does C15H32 belong?
    ................................................
    (ii) Use the equation above and your answer to (a)(ii) to calculate the amount, in moles,
    of H2O2, that will provide sufficient oxygen for the complete oxidation of one mole
    of C15H32.
    amount of H2O2 = ................................. mol
    How to do the last part
     
  10. Hamnah Zahoor

    Hamnah Zahoor

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    First, calculate the number of moles of oxygen
    (46*16)/32=23 moles
    than place this number of moles equal to number of moles of oxygen produced in reaction 1
    For finding the number of moles of H2O2 multiply it by 2
    2(23)=46 Moles
     
  11. Holmes

    Holmes

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    Answer is here in pdf file:

    Dude I hope I helped.
     

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  12. Raheel616

    Raheel616

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    Concentrated sulfuric acid behaves as a strong acid when it reacts with water
    H2SO4 + aq => H^+ + H2SO4^-
    The HSO4^- ion behaves as a weak acid.
    H2SO4^-(aq) <=> H^+(aq) + SO4^2-
    Which statements are true for 1.0 ml dm^3- sulfuric acid?

    1. [H^+(aq)] is high
    2. [SO4^2- (aq)] is high
    3. [HSO4^-(aq)] = [SO4^2-(aq)]

    Please explain the answer and reason? (Only statement 1 is correct)
     
    Last edited: Mar 13, 2018
  13. Metanoia

    Metanoia

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    H2SO4 + aq => H^+ + H2SO4^-
    Due to full dissociation at the first stage, from 1 mole of H2SO4, we will get 1 mole of H+ and 1 mole of HSO4^-

    HSO4^-(aq) <=> H^+(aq) + SO4^2-
    Due to partial dissociation at the second stage, from 1 mole of HSO4^-, we will get << 1 mole of H+ and << 1 mole of SO4^2-

    Therefore
    [SO4^2- (aq)] is low
    [HSO4^-(aq)] >> [SO4^2-(aq)]
     
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  14. Fathima Hd

    Fathima Hd

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    9701/12/m/j/ 16 ques 14
    Answer is D
    Please explain the answer
     

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  15. Hamnah Zahoor

    Hamnah Zahoor

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    Write a complete balanced equation for the thermal decomposition of Ca(NO3)2
    i.e Ca(NO3)2---->CaO+2NO2+0.5O2
    As you can see that total volume of gas produced is 2.5 moles thus from previous informations
    1 mole of CaCO3 producing 1 mole of CO2
    0.005----->100cm3
    1 mole of Ca(NO3)2 producing 2.5mole of Gas
    0.005----->250cm3
    thus, D is the answer.
     
  16. Holmes

    Holmes

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    upload_2018-3-18_9-38-5.png
    upload_2018-3-18_9-40-37.png
    Help me out with part (iii)
     
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  17. Hamnah Zahoor

    Hamnah Zahoor

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    As you calculated the total number of chiral centres in part (ii) 2 thus total optical isomers will be 2^2=4
    When the molecule is unsymmetrical and contains ''n '' chiral carbon atoms, Total no. of stereoisomers = 2^n.
     
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  18. Holmes

    Holmes

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    Thanks. :cool:
     
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  19. Holmes

    Holmes

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    Can anyonne help me rather guide me on Chemistry P5 . I don't know a single word of it. Kindly provide me some source of preparation of Chemisry P5.
     
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  20. Holmes

    Holmes

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    Can anyone upload a single solved Chemistry P5. PLZ!
     
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  21. abbas haider

    abbas haider

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