what's the difference between an A+ student or A-, it's the simple mistakes, careless. so here are some of the common mistakes in SPM Chemistry. take note guys! sometimes, it's the little things yang buat gred kita dari A turun B, and so on..
this common mistakes dari paper SPM Chemistry 2010. so bila buat buku past years tu, tengok la kertas 2010, paper 2 okay ;)
PAPER 2 SECTION A
this common mistakes dari paper SPM Chemistry 2010. so bila buat buku past years tu, tengok la kertas 2010, paper 2 okay ;)
PAPER 2 SECTION A
Students must write chemical formula and not chemical name.
Correct answer: SO3
Example 2Sulphuric acid produced is mixed with water in a beaker. State the observation if a piece of marble is dropped into the beaker. (Asid sulfurik yang terhasil dilarutkan ke dalam bikar berisi air. Nyatakan pemerhatian jika sebutir marmar dimasukkan ke dalam bikar itu.) Q1 (a) (vi)
Wrong answer: Carbon dioxide / Oxygen / Nitrogen gas is released.
Students are required to write the observation (through your naked eyes) not the type of gasor the name of the solutions. Students cannot see the gas molecule (unless students have Superman’s eye)
Correct answer: Bubbles of gas are released // Gas bubbles are released // Effervescence occurs in the beaker
(Also accept: Beaker becomes warm // mass of marble decrease)
Example 3State one use of ammonium sulphate in daily life. (Nyatakan satu kegunaan ammonium sulfat dalam kehidupan seharian.) Q1 (c) (ii)
Wrong answer: fertilizer / fertiliser
Students answer is not complete and did not state the use.
Correct answer: As fertilisers / Used as a fertiliser / Ammonium sulphate is used asfertiliser in daily life.
Example 4State the melting point of substance P. (Nyatakan takat lebur bahan P.) Q2 (a) (ii)
Wrong answer: 83 / 83˚
Without measuring unit, the answer is considering wrong response. The measuring unitmust include in the answer and the measuring unit must be correct.
Correct answer: 83˚C
Example 5State the physical state of P from time t1 to t2. (Nyatakan keadaan fizikal P dari masa t1 to t2) Q2 (a) (iii)
Wrong answer: solid
There are two physical states present from t1 to t2.
Correct answer: solid and liquid
Example 6Explain why the temperature remains constant from t1 to t2. (Terangkan kenapa suhu tidak berubah dari masa t1 to t2.) Q2 (a) (iv)
Wrong answer: To overcome the force of attraction between atoms.
From the prediction (also one of the PEKA experiment in Form 4), solid P is naphthalene so it should be molecules not atoms.
Correct answer: is used to overcomes the forces of attraction between the molecules /particles P // It is because the heat energy absorbed is used to overcomes the force of attraction between particle so that solid P can melt into liquid state. // The heat absorbed by particles of substance P is used to overcome the forces holding the particles in fixed positions.
Example 7Write the formulae for all anions that are present in sodium chloride solution. (Tuliskan formula bagi semua anion yang hadir dalam larutan natrium klorida.) Q3 (a) (ii)
Wrong answer: hydroxide ions, chloride ion
The question is asked for the formulae not chemical name, so students are required to read the question carefully.
Correct answer: Cl- , OH-
Example 8Describe a test to indentify the gas collected at the cathode. (Huraikan satu ujian untuk mengenalpasti gas yang terkumpul di katod) Q3 (b) (iii)
Wrong answer: A burning / glowing wooden splinter is inserted into the test tube.
To test hydrogen gas – a lighted wooden splinter is used.
To test oxygen gas – a glowing wooden splinter is used.
To test chlorine gas – a damp blue litmus paper is used and litmus paper will be decolourised.
Another mistake is ‘inserted’. Students should use place or put into the test tube.
Correct answer:
1) Place a lighted wooden splinter into the test tube // A lighted wooden splint isplaced into the test tube of the cathode
2) A ‘pop’ sound is produce / can be heard // The presence of the gas will cause the lighted wooden splinter to burn with a ‘pop’ sound.
Example 9Give a reason for your answer in (c) (i). (Beri alas an bagi jawapan anda di (c) (i).) Q3 (c) (ii)
Wrong answer: Because hydroxide ion is more reactive.
Students should give explanation by discussing the position in electrochemistry series.
Correct answer: Because hydroxide ion is located lower than chloride ion inelectrochemistry series.
Example 10
Name a substance that can replace bromine water. (Namakan satu bahan lain yang boleh menggantikan air bromine.) Q4 (a) (iv)
Wrong answer: KMnO4 / Iodine water
Students must name the substance not give chemical formula. Besides that, the solution must be present.
Correct answer: Acidified potassium manganate(VII) solution // Acidified potassium dichromate(VI) solution // Chlorine water.
Example 11What is the function of dilute sulphuric acid? (Apakah fungsi asid sulfurik cair?) Q5 (a)
Wrong answer: to separate the two solutions.
This is not the main function of dilute sulphuric acid and zero mark will be given.
Correct answer: To complete the electric circuit // To complete the flow of electric current throughout the circuit // To allow movement of ions.
Example 12State the observation at carbon electrode X. (Nyatakan pemerhatian di elektrod karbon X.) Q5 (b) (i)
Wrong answer: solution turns yellow.
For all the observation (colour changes), students must state the colour of the solution beforereaction and after the reaction or ‘the xxx colour of the solution turns / changes yyy colour’. In simple words, it must have before changes and after changes.
Correct answer: Green colour solution turns to brown / yellow.
Example 13State the observation at carbon electrode Y. (Nyatakan pemerhatian di elektrod karbon Y.) Q5 (c) (i)
Wrong answer: It decolourise / It turns colourless.
Similar to example 12, students must describe the colour before changes.
Correct answer: Purple colour solution is decolourised / turns colourless // The purple acidified potassium manganate(VII) solution turns colourless.
Example 14What is alkali X?
Wrong answer: Potassium hydroxide, KOH
For this question, chemical formula and/or chemical name are accepted. Only concentrated sodium hydroxide will be use in the production of soaps and glycerol.
Correct answer: Concentrated sodium hydroxide / Concentrated NaOH.
PAPER 2 SECTION B
1) Can students use point form technique in answering essay question?
Yes, in SPM Chemistry Paper 2 (essay) students are allow to use point formed but it must be acomplete sentence. (I don’t encourage students to do so unless students have language barrier or not enough time to answer the question.)
Example 1
Describe the formation of the following chemical bonds and draw the electron arrangement of compounds formed. (Huraikan pembentukan bagi ikatan kimia berikut dan lukis susunan electron bagi sebatian yang terbentuk.)
- Ionic bond between magnesium atom and chlorine atom. (Ikatan ionic antara atom magnesium dengan atom klorin.) Q7 (b) (i) (5 marks)
Wrong answer/technique:
- Magnesium atom donates.
- Releases 2 electrons to form magnesium.
- Chlorine atom accepts.
- Receives 1 electron to form chloride.
- Achieve electron arrangement.
- Magnesium and chlorine are attracted by electrostatic force.
No marks will be given if students did not provide a complete sentence and clear answer.
Correct answer:
- Magnesium atom donates two electrons to form magnesium ion which achieve stable electron arrangement.
- Chlorine atom accepts one electron to form chlorine ion which achieve stable electron arrangement.
- Magnesium ion and chloride ion are attracted to one another by electrostatic force.
2) Can students use table for comparison or explanation?
Yes, it is highly recommended by most of the Chemistry teachers. Students would not miss out any important key-points.
Example 2
Explain each of the following statements. (Terangkan setiap pernyataan berikut.)
- Compound formed in (b) (i) can conduct electricity in the molten state while compound formed in (b) (ii) cannot conduct electricity in any state. (Sebatian yang terbentuk dalam (b) (i) boleh mengkonduksikan elektrik dalam keadaan leburan manakala sebatian yang terbentuk dalam (b) (ii) tidak dapat mengkonduksikan elektrik dalam semua keadaan.) Q7 (c) (i) (4 marks)
Correct answer:
| MgCl2 | CCl4 |
| Ions in MgCl2 are held together by strong electrostatic force. | Molecules in CCl4 are held together by weak intermolecular forces / van der Waals. |
| MgCl2 need a lot of heat energy to overcome the strong electrostatic force / fixed crystal lattice structure. | CCl4 need less energy to overcome the forces. |
3) How to get full marks for the graph?
Students need to make sure that your graph must consist of 3 important things
(SAL / SAP)
S = Shape of the graph
A = Axis (must correct and labeled with units)
L / P = Label / Points plotted
A = Axis (must correct and labeled with units)
L / P = Label / Points plotted
And do remember to write the title of the graph.
4) Is the unit important for the calculation?
Yes. Students need to include the unit in the final answer.
Example 3
Diagram 8 shows the energy level diagram of the heat of combustion of ethanol. Calculate theenergy released if 6.9 grams of ethanol is burnt completely in air.
(Rajah 8 menunjukkan gambarajah aras tenaga bagi haba pembakaran ethanol. Kira haba yang dibebaskan jika 6.9 gram ethanol di bakar dengan lengkap di dalam udara.) Q8 (d) (ii) (4 marks)
Wrong answer:
Number of mole of ethanol = 6.9 / 46 = 0.15
0.15 mole will form 0.15 x 715 = 107.25 kJ mol-1
0.15 mole will form 0.15 x 715 = 107.25 kJ mol-1
Correct answer:
Number of mole of ethanol = 6.9 / 46 = 0.15
0.15 mole will release 0.15 x 715 = 107.25 kJ of heat
0.15 mole will release 0.15 x 715 = 107.25 kJ of heat
PAPER 2 SECTION C
1) Is it a compulsory to draw experimental
diagram?
No.
It is not compulsory to draw experimental diagram unless it is stated in the
question.
2) What are the techniques in writing these procedures?
Each
sentence or procedure step must have this combination to form a sentence.
3) How to write procedure of
the experiment?
Students
are always confused with whether to use active formed sentence or passive
formed sentence. The answer is no penalty but students can choose only one
form. It is different
from the PEKA experiments procedure which must be in passive form sentence. So
I would usually recommend my students to write passive form
sentence (past
perfect tense) in PEKA experiments and experimental essay (Section C).
Example 1
Correct answer candidate A (passive
form – past perfect tense):
Correct answer candidate B (passive
form – present perfect tense):
Correct answer candidate C (active form):
4) Is it a compulsory to give example for the experiment?
Yes.
Students need to give an example of the material.
Example 2
Wrong answer:
|
Description
|
Mass (g)
|
|
Crucible
+ lid
|
|
|
Crucible
+ lid + metal
|
|
|
Crucible
+ lid + metal oxide
|
|
Correct answer:
5
cm of magnesium ribbon was cleaned with sandpaper.
…
|
Description
|
Mass (g)
|
|
Crucible
+ lid
|
|
|
Crucible
+ lid + magnesium
|
|
|
Crucible
+ lid + magnesium oxide
|
|
(Students do
not need to
include the value of mass unless it is given in the question.)
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