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Chemistry: Post your doubts here!

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

  1. emily kwong

    emily kwong

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    CAN SOMEONE PLEASE HELP ME!! :)

    Group 1 nitrates decompose on heating to produce oxygen and metal nitrite, MNO2 (M = Na, K, Rb or Cs). When a particular Group 1 nitrate, MNO3, was heated until no further change occurred, it lost 10.85% of its mass. Calculate the Ar of M and hence identity it.

     
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  3. emily kwong

    emily kwong

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    why does K+ have a greater ionic radius than Na+?
     
  4. Ebrahim12

    Ebrahim12

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    K+ has one more electron shell than Na+
    K+: 2,8,8
    Na+: 2,8
    As you go down the group, both the ionic and atomic radii increase.
     
  5. Neurotransmitter

    Neurotransmitter

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    In flooded soils, like those used for rice cultivation, the oxygen content is low. In such soils, anaerobic bacteria cause the loss of nitrogen from the soil as shown in the following sequence. In which step is the change in oxidation number (oxidation state) of nitrogen different to the changes in the other steps?

    NO3 – (aq) A NO2 – (aq) B NO(g) C N2O(g) N2(g)


    The answer is A . Please help !!!
     
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  6. Hamnah Zahoor

    Hamnah Zahoor

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    [​IMG]
     
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  7. Neurotransmitter

    Neurotransmitter

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    Why is 2 and 3 not included? Is it because we're considering about isotopes so isotopic mass and nucleon number may be different?
     

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  8. Ebrahim12

    Ebrahim12

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    Yes.
    Molecular mass: sum of atomic masses of atoms in a molecule
    Atomic mass: weighted average of isotopic masses
    Isotopic mass: mass of isotope

    (All relative to 1/12th of C-12)

    The sample is going to have different stable carbon isotopes with different masses. The atomic mass derived from the sample is the weighted average of these different masses.
     
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  9. Shemyaa

    Shemyaa

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  10. Neurotransmitter

    Neurotransmitter

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    THANKS :)
     
  11. Neurotransmitter

    Neurotransmitter

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    the ideal gas equation: pV=nRT.

    now if you rearrange the equation, you'll get pv/RT=n. So n will always have a constant value for a fixed mass of gas. Hence the expected graph for pV/RT against p should be a horizontal line.

    EXTRA: If you want to plot a graph having the same axes but with a different mass of gas, the graph would be a different horizontal line...nothing much. Think about plotting a graph of mass of gas trapped inside a cylinder as you push in the piston to change the pressure. The mass never changes
     
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  12. Neurotransmitter

    Neurotransmitter

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    32 Use of the Data Booklet is relevant to this question.

    In which pairs do both species have the same number of unpaired p electrons?

    1 O and Cl +
    2 F+ and Ga–
    3 P and Ne+




    I don't get the part 2. The answer is 1 and 2 but I gave 1 now I don't understand how 2 is also included
     
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  13. Neurotransmitter

    Neurotransmitter

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    Answer is 1 only. How???? Why not the others?
     

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  14. Shemyaa

    Shemyaa

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    Thank you :)
     
  15. Shemyaa

    Shemyaa

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    upload_2019-1-15_16-53-36.png
    I got the answer but I had to touch my nose to do that, Can someone share maybe another way?
     
  16. Shemyaa

    Shemyaa

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    You have to remember that in an equilibrium reaction there is no maximum yield,
    H+ ions are in a higher concentration compared to the other products since its formed twice, when sulfuric acid dissociated and when HSO4- dissociated.
    Try setting your own values like volume of H2SO4 and you'll get what I mean.
    Hope it helped!
     
  17. Shemyaa

    Shemyaa

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    O AND CL+ - There electronic configuration is as follows:
    [He]+2s2 2p4 , [He]+2s2 2p4 (since chorine lost one e )

    F+ AND Ga- - There electronic configuration is as follows:
    [He]+2s2 2p4 , [He]+2s2 2p6, 3s2 3p6 , 4s2 , 3d10 , 4p2

    To actually understand this, you want to draw the orbitals and fill them. You'll realise for part one regards 2p4 lets say () is the orbital. And we know that a p subshell has 3 orbitals. there fore
    (11)(1)(1) [the paired e are in opposite direction] [you can see there are 2 orbitals that are half filled]
    In the second example,
    for 2p4 (11)(1)(1) and for 4p2 , (1)(1)() [You can see here that also both have two orbitals

     
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  18. Hamnah Zahoor

    Hamnah Zahoor

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    Untitled.png
     
    Last edited: Jan 15, 2019 at 4:35 PM
  19. Hamnah Zahoor

    Hamnah Zahoor

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    Neurotransmitter I hope this helps
     

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