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2017年4月12日

2017 DSE Chem suggested answer 化學科 答案 + 感想




Paper 1B      
Paper 2       

Marking Scheme by DSE00 (just drafted version)


以下答案純粹草稿答案
      Paper 1A  (drafted answers)
1      CDABD          6     CACAA
11    BBDAB          16    AABDD
21    CDBCB            26    BCDAA
31    BCCDC          36    C

      Paper 1B  (drafted answers)
以下答案純粹草稿答案

SECTION B
PART I

1        (a)     I don’t draw la.
(b)      (i)     NH3 has lower density than air
(ii)    NH3 is soluble in water.

         (c)    (i)     temperature raise
                  (ii)    (1)    Ba2+ react with SO42- to form insoluble BaSO4.
                                    The concentration of mobile ion decrease.
                           (2)    H2SO4 dissolve in water and dissociate to give mobile ion H+ and SO42-

2       (a)    Copper does not corrode.
                  Iron corrode and become rust which loosely attach to the surface of the water pipes                  
                  and peel off.                 
         (b)    (i)     Joint two metal water pipes by forming metallic bond between two pipes.
                  (ii)    Lead is toxic to human.

         (c)    (1 x 10-8 / 207.2) / 0.001 = 4.83 x 10-8 mol dm-3


3       (a)    Propene has C=C double bond.
         (b)    HO2C(CH2)4CO2H has two carboxylic acid group which can form continue amide                
                  bond with amine group of H2N(CH2)6NH2.
         (c)    Dative covalent bond is formed when all the bonding electrons are contributed by             
                 same atom.
Oxygen donate a lone pair electron to hydrogen atom.
        
4       (a)    (i)     Colourless
(ii)    Red
         (b)    H2O(l) à H2(g) + O2(g)
         (c)          (i)     no
(ii)    yes, colourless instead red could be observed.
         1M H2SO4 is acidic solution.

5        All of them has simple molecular structure, the boiling point depends on the strength of intermolecular force.
           H2 and F2 has lower boiling point than HF because only HF among three molecule can form hydrogen bond.
           H2 has lower boiling point than F2 because H2 has the smaller molecule size among three atom so the intermolecular force is the weaker.
           Higher energy is needed to overcome stronger intermolecular force.

6       (a)    The second ( oxidative) and third (corrosive)
         (b)    (i)     The reaction of conc H2SO4 and NaOH is highly exothermic.
                           The solution may spill out and cause accident.                                   
                  (ii)    Change from red to orange.

                  (iii)   NaOH used = 0.0222 x 0.189 = 0.0041958 mol
                           H2SO4 used = 0.0041958 /2 =0.0020979 mol
                           [H2SO4] before dilution = 0.0020979 / 0.025= 0.083916 mol dm-3
                           [H2SO4] after dilution =  0.083916 x (1000/5) =16.8 mol dm-3

         (c)    Blue solution form / Copper dissolve / Colourless gas bubble evolve / Temperature                   raise
                  Cu à Cu2+ + 2e-
                  2e- + SO42- + 4H+ à SO2 + 2H2O
                  Cu + SO42- + 4H+ à Cu2+ + SO2 + 2H2O

7       (a)    Side products are formed /
                  Formation of C2H2 involves high activation energy
         (b)    Hess's law states that the change of enthalpy in a chemical reaction is independent                   
                 of the  pathway between the initial and final states.        
         (c)    (i)     I don’t draw la.
                  (ii)    (1)    25C and 1 atm pressure
                           (2)    AH= -1300 + 286 + 394x2 = -226 kJ mol-1

8       (a)    2C8H18(l) + 25O2(g) à 8CO2(g) + 9H2O(l)
         (b)    I don’t draw la.

         (c)    FOR:                electric car is higher energy efficiency
                  AGAINST:       electricity come from burning fossil fuel

         (d)    Insufficient oxygen
         (e)    (i)     catalytic convertor
                  (ii)    SO2

9       Add Br2, only CH2=CHCO2H can turn Br2 from orange to colourless.
         Add NaHCO3, only CH3CH2CO2H give colourless bubble.
         Add K2Cr2O7/H+, only HOCH2CH2CH2OH turn from orange to green.

10     (a)    1M
         (b)    I don’t draw la, fast at first, slow then, reach maximum at 60 cm3
         (c)    Temperature only affect the rate of reaction.
         (d)    mass. O2 escape and the mass decrease through the progress.

11     (a)    I don’t write la, just as normal one.
         (b)    49752 : 1
         (c)    The intensity of yellow colour increase. NaOH react with H+
                  [H+] decrease.
                  Equilibrium position shift right.
                  More 4-nitrophenoxide ion form.
         (d)    indicator.

12     (a)    I don’t draw la.
         (b)    (i)     (OH replace Br)
                  (ii)    substitution

         (c)    (i)     (C=C exist at the 1st carbon, keep the OH group at 3rd)        
                  (ii)    Hydrogen gas with Platinum catalysis.

13     I don’t draw la.
         Use H2SO4 to break the ester bond)
         Use LiAlH4/H+, dry ether to reduce the carboxylic acid group

14     -Coloured
         Mn2+ produced is pink in colour
         -More than 1 oxidation state
         Mn can be +7 and +2
         -Catalytic properties          
         Rate is slow at first and fast later show the production of Mn2+ ion catalyze the   reaction.

感想

伏位幾多,温得唔熟或思考唔夠仔細嘅同學好易中伏,例如 Q9 hydrogen-oxygen fuel cell catalyst,書好似無乜點講,但如果記得 O2 cathode 甘就無問題。Q22 用左 acidic , non-acidic poisonous, non-poisonous 字眼,你除左要知道會產生 CO2, H2O CO 之外,仲要知道佢地既properties 先做到。又例如Q2, Q6, Q15, Q24, Q25, Q30, Q36 都係比較伏既地方 ( 注:伏同難唔同,伏:以為自己做岩左;難:唔識做 )


但對於一貫 Lv5 以上/ 熟練 Past paper 同學仔難度應該不大,因為呢 D 伏位以前都出過 =]  

不過難其實唔難,係有 D 伏,應該比 2016 易,但比 2016 伏。 

LQ 方面,唔難,好直接 =]

2 則留言:

  1. 答案謹供參考,如有錯漏,有請不吝指正

    回覆刪除
  2. 題2bi:
    加lead ge 目的唔係forming alloy 咩?
    同metallic bonds 有什麼關係?

    回覆刪除

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