5** 化學知識 (高程度) + DSE 伏位破解

 課題選擇      1       2A       2B       3A      3B       3C, 4     TOP 

  1      Planet Earth and The Microscopic World and Metal (微觀世界+金屬)

  4   The most abundant element in the world is oxygen and the most abundant metal in the world is aluminium

  3   The chemical nature of lime water is Ca(OH)2

  2   Flame test is not a test for metal but metal ion. For example, golden yellow flame can be observed when NaCl is burning. When sodium is burning, metal Na turn to Na2O and Na+ in Na2O give golden yellow color

焰色測試是測試金屬離子而不是金屬,例如燃燒 NaCl,可以看見金黃色火焰。燃燒Na 時,金屬Na 轉為Na2ONa2O裡的Na+ 把火焰轉為黃色

  1   The "molar mass" of air is around 29 g mol-1 which can be obtain by following formula

molar mass of air = N2 x 78% + O2 x 21% = 28.56 g mol-1

If the molar mass of a gas is smaller than air, it density is lower than air and we should use an suitable method to collect the gas.

空氣的「摩爾質量數」大約是 29 g mol-1,是這樣計算出來的

空氣的「摩爾質量數」     =    N2 x 78% + O2 x 21%
=    28.56 g mol-1

(Others coming soon =) )

  2A       Acid and Base (酸和鹽基)  

  4   Concentrated H2SO4 is corrosive since it will dehydrate our skin and damage our skin by oxidation.

(1997 Q39)

  3   Strength of acid depend on its degree of dissociation into ion but not its concentration.
(1996 Q49)

  2   All the oxide, hydroxide, carbonate are insoluble except group I element such as
Na2O, K2O, Li2O as well as NH4+

例如Na2O, K2O, Li2O NH4+

  1   HNO3 has rather low boiling point around 90. So HNO3 is volatile.
Also nitric acid react with metal by redox reaction but not typical acid reaction. 
2HNO3 + 2H+ + Zn NO2 + H2O + Zn2+
As you can see from the equation, NO2 instead of H2 is produced in the reaction.

HNO3 的沸點大約在90℃,所以它是揮發性的。HNO3也會和金屬反應,不過是氧化還原反應,而非一般酸和金屬的反應。從上面的方程式可見,NO2 在反應中產生了,而非H2

(Others coming soon =) )

  2B      Redox  (氧化還原)  
        (Others coming soon =) )

  3A      Fossil Fuels and Carbon Compunds (化石燃料和碳化合物)

  4   Warm house gas include CO2, CH4, CCl2F2, NO and O3.
温室氣體有CO2, CH4CCl2F2, NO and O3.

  3   Polystyrene is a packing material

36. Which statements concerning polystyrene is/are correct?
(1) It is a condensation polymer.
(2) It can be remoulded.
(3) It can be used to make packaging material for electrical appliances.
A.   (1) only.
B.    (2) only.
C.   (1) and (3) only
D.   (2) and (3) only 
                                                                      ANS(highlight to see): D

 2  Leaded petrol is being banned in Hong Kong

47.         statement 1
The use of leaded petrol has been banned in Hong Kong
statement 2
Lead compounds in car exhaust can cause damage to human brains.
                                                                               ANS(highlight to see): B

 1  Hard water is a water containing Ca2+, Mg2+. They will form ppt with anion of detergent.

29. Which of the following substances is/are responsible for the hardness of water?
(1) Sodium chloride.
(2) Calcium chloride.
(3) Potassium chloride.
(4) Magnesium chloride.
A.   (1) only.
B.    (2) only.
C.   (1) and (3) only
D.   (2) and (4) only
                                                           ANS(highlight to see): D

        (Others coming soon =) )

  3B      Organic Chemistry (有機化學)

  1   教你Enantiomer / identical  學識以100% 

(Others coming soon =) )

  3C  4      Energy,     Rate,     Equilibrium  (能量和平衡)

  6   EEquilibrium       (PP Q26)
               Shift to the side to pressure

                  E.g        2 A(g) B(g)                             A 3B
                                 Shift to B                                  Shift to A
  5    SPQ29

A B       ∆H = +100 kJ mol-1 
If temperature decrease, what would be the effect on the rates of the forward and backward reactions?

     forward reaction rate      backward reaction rate

A.    decreases                          increases
B.    decreases                          no change
C.    decreases                          decreases
D.    increases                          decreases                ANS(highlight to see): C   

T , Kc also for endothermic reaction.
Kc just mean the rate of forward reaction > backward,
But not mean rate of forward reaction , backward

  4       SPQ33
S2O32-(aq)  +  2H+(aq)  →   SO2(g)  +  S(s)  +  H2O(l)
Which of the following apparatus should be used when carrying out the above experiment?
(1) syringe 
(2) stop watch 
(3) measuring cylinder

A. (1) and (2) only
B. (1) and (3) only
C. (2) and (3) only
D. (1), (2) and (3)                                    ANS(highlight to see): C    

Syringe does not work although SO2 is produced. Because SO2 is soluble in water. Thus gas collection only work for which is not soluble in water.

  3       Colourimeter
               Absorbance means the amount of light absorbed by solution.

  2       Catalyst
       2 ∆-∆     C = catalyst

         Step 1                           + C          -- C
  Step 2           -- C + -- C             2 -- + 2C
      formation of -- C has lower activation energy than -- directly.

  1       Solubility
The compound with low bond breaking energy always has higher solubility.
l   weaker bond, higher solubility.

(Others coming soon =) )