2017 DSE Chem suggested answer 化學科答案 + 感想

Paper 1A

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) Metallic bond exists between the Ba²⁺ ion. Each of the Ba atom donates two

electrons to form a ‘sea’ of electron that surrounds the Ba²⁺ ion.

(b) (i) NH₃has lower density than air

(ii) NH₃ is soluble in water.

(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 SO₄^2-

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.

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.

Oxygen donate a lone pair electron to hydrogen atom.

4 (a) (i) Colourless

(ii) Red

(b) H₂O(l) à H₂(g) + O₂(g)

(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

Cu à Cu²⁺ + 2e^-

2e^- + SO₄^2- + 4H⁺ à SO₂ + 2H₂O

Cu + SO₄^2- + 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.

(ii) (1) 25C and 1 atm pressure

(2) AH= -1300 + 286 + 394x2 = +226 kJ mol^-1

8 (a) 2C₈H₁₈(l) + 25O₂(g) ---> 16CO₂(g) + 18H₂O(l)

(b) I don’t draw la.

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

(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

[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

(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 有catalyst，書好似無乜點講，但如果記得 O2 係 cathode 甘就無問題。Q22 用左 acidic , non-acidic 同 poisonous, non-poisonous 嘅字眼，你除左要知道會產生 CO2, H2O 同 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 )