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2017-12-28

2018 DSE00 Chem Mock 1A





Paper 1A        version 2.0             (30/12/2017)
Paper 1B       
Marking         version 2.1             (31/12/2017)
                     

發問指引
1.       列出卷號、題號、分題號。請依據以下格式
      Q13
2.       發問前請先 Control + F 搜尋題號,確保沒有重覆發問。
3.       這是 2018 1A 解答區。

請在下面留言區發問 =〕

其他年份
2017          (2017 解答)
2016          (2016 解答區)
2015          (2015 解答區)

48 則留言:

  1. 1A Q1 atom唔會有一樣既electronic arrangement,ion先有
    Q9 NH4Cl 並唔系oxidizing agent,因為反應中oxidation number無變
    Manganese(IV) oxide 先系反應中既oxidizing agent
    MN 由+4變+3
    Q18 (a)(i)佢地唔系都係同1group咩?
    Q20 (3)geometrical isomerism指既應該系 cis-trans,而唔系enantiomer

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    1. 回18 ai
      To my knowledge, Homologous series can be expressed using the same general formula, I.e. CnHn, so I think as CnH2n+1OH and CnH2n(OH)2 are two different general formula, so they are not in the same homologous series.
      路人純9Up, 想搵人Confirm 下

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    2. 1AQ1
      I aware some concept is outC, so I amend some of the option. Thanks

      1AQ9
      NH4+ + e ---> NH3 + H2
      H is reduced from +1 to 0 so it is OA.

      1AQ18 no, they belong to different group because they cant be represented by same general formula.

      1AQ20
      you are right. I change "geometrical" to "stereoisomer" Thanks!

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    3. re 1AQ9
      NH4+ + e ---> NH3 + H2
      2MnO2+H2 --->Mn2O3+H20
      but H2 is cancelled out in the process
      by樓主

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    4. I agree that there's problem in wording. I try to use other word to correct it. thanks

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    5. Q34(2)
      Mole ratio of the reactants to product is 3:2 in the forward reaction.Thus,increasing the pressure of the system shifts the equilibrium position to the right to reduce the volume of the gas and hence opposing the increase of pressure.In this sence,isn't (2) wrong?
      thx

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    6. Re Q.34 (2)
      should be both forward and backward rate increase (?)
      but forward reaction rate > backward reaction rate

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    7. 1AQ34
      樓上 is correct, both rate increase

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    8. Can someone explain Q34(2),i still don't get it.
      Thx

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    9. higher pressure = higher concentration = higher rate. Just like higher temperature can increase both forward and backward rate. But forward rate increase more so the reaction shift right.

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  2. ms
    29. The systematic name should be heptana-2,4,6-triol
    應該系叫heptane-2,4,6-triol

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    1. 1AQ29
      Yes, you are right, some typo occur

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  3. P1AQ18
    想問點解option C錯
    Mass of A < mass of B
    Mole of A present in 1g > mole of B
    加上B 比A多一個O atom
    Gum唔係A要多D O2去complete combustion?
    Thx

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  4. 1A Q23 option 3,
    想問D GAS 係點來?
    Thx

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  5. 1A Q36 "Both calcium and magnesium can react
    with water." why false?

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    1. Magnesium can only react with steam

      Mg (s) + 2H2O(g) -> Mg(OH)2(aq) + H2(g)

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    2. I have a few questions
      What I have learnt in textbook is that Mg can react with hot water and steam.
      Mg+steam=MgO+hydrogen gas
      Mg+hot water=magnesium hydroxide+hydrogen gad

      Why my knowlegde is different from others? Different version of chemical knowledge? or mistakes made by the textbook?
      My textbook is HKDSE Chemidtry A modern view second edition by Aristo Education Press Ltd

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    3. you are right according to the syllabus of DSE.

      for more information, check here
      https://www.chemguide.co.uk/inorganic/group2/reacth2o.html

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    4. Q36 statement 1 is too controversial.
      Magnesium in fact reacts even with cold water, though very slowly.

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  6. 1A Q5 why the ans is C, not B or D?

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    1. 1AQ5
      electrode B is positive charged, Cl- go to B and discharged to Cl2.

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  7. 1A Q33 why form precipitate

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    1. I think although the carboxylic acid formed can form hydorgen bond with water,the long carbon chain make it barely soluble in water,thus forming white precipitate

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    2. 樓上 is correct. The ratio of C and OH is 4:1 to make the molecule soluble

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  8. 1A Q23 why Zn and KMnO4/H+ would not form pale pink solution?

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    1. oh yes, the answer should be A. I forget why I type B at that moment.

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    2. MnO4- get electron instead of H+, so no gas is produced la

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  9. 1AQ32
    why (3) is incorrect?the equilibrium position shifts to the right which produces less gases?

    1AQ2
    A should it be ionizes instead of dissociates?

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    1. Re 1AQ32(3),since the mole ratio of the reaactant to product is 2:2,which equals to 1:1,no matter how the equilibrium position shifts,it would produce the same volume of gases

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    2. 1AQ32 same to above =]

      1AQ2 Both ionize and dissociate can be used for acid

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  10. 1AQ1
    The question said covalent compound is formed, how come the answer is not PCl3 which is a covalent compound, but GaCl3 which is an ionic compound?

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    1. For PCl3, P is Group V element while Cl is Group VII element. Different electronic configuration.

      For GaCl3, it is covalent compound, with bitetrahedral structure. Similar example is AlCl3. It is not definitely that metal and non-metal will form ionic compound. There is actually no clear-cut.

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  11. 1AQ14
    option b said that Chlorine gas can turn moist pH paper white. Why is it right? I think chlorine gas can only turn moist LITMUS PAPER white

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    1. the OCl- is bleaching agent anyway, so it doesnt matter if it is pH meter or litmus paper

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  12. 回覆
    1. let it be M2Ox

      M2Ox --> 2M
      5g --> 4.44g

      5/(2*65.4+16x)=4.44/(2*65.4)
      x=1

      so, M2O

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  13. 可否每題都簡單講下點解ans係_?

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    1. just ask which one you dont understand coz difficult to type all

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  14. 1AQ14:
    What is the white fume when Cl2 is mixed with NH3 gas?
    Q16:
    Statement 1: Does "nitrogen" in this statement mean nitrogen atom, or nitrogen molecule?
    Thank you.

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    1. NH4Cl(Q14)
      Seems molecule(Q16)

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  15. 回覆
    1. 3MgCO3 + 2H3PO4 --> Mg3(PO4)2 + 3CO2 + 3H2O
      10g = 0.1186 mol
      0.1186/3*2 = 0.08 mol, but H3PO4 only 0.06 mol, is limited.
      CO2 volume = 0.06/2 *3 *24 = 2.16 dm3


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  16. Q31 how to calculate?

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  17. What is the explanation for Q2's answer

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