Common Mistakes Made by Students in SPM Chemistry Paper 2

Common mistakes made by students in SPM Chemistry Paper 2 (Section A) Example 1 Write the chemical formula of sulphur trioxide. Q1 (a) (iii) Students must write chemical formula and not chemical name. Correct answer : SO3

Example 2 Sulphuric acid produced is mixed with water in a beaker. State the observation if a piece of marble is dropped into the beaker. Q1 (a) (vi) Wrong answer : Carbon dioxide / Oxygen / Nitrogen gas is released.

Students are required to write the o bservation (through your naked eyes) not the type of gas or 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 3 State one use of ammonium sulphate in daily life. . 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 as fertiliser in daily life.

Example 4 State the melting point of substance P. Q2 (a) (ii) Wrong answer : 83 / 83˚

Without measuring unit, the answer is considering wrong response. The measuring unit must include in the answer and the measuring unit must be correct. Correct answer : 83˚C

Example 5 State the physical state of P from time t 1 to t2. Q2 (a) (iii) Wrong answer : solid

There are two physical states present from t 1 to t2. Correct answer : solid and liquid

Example 6 Explain why the temperature remains constant from 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 7 Write the formulae for all anions that are present in sodium chloride solution. 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 8 Describe a test to indentify the gas collected at the cathode. 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 is placed 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 9 Give a reason for your answer in (c) (i). Q3 (c) (ii) Wrong answer : Because hydroxide ion is more reactive.

Students should give explanation by discussing t he position in electrochemistry series. Correct answer : Because hydroxide ion is located lower than chloride ion in electrochemistry series .

Example 10 Name a substance that can replace bromine water. Q4 (a) (iv) Wrong answer : KMnO4 / Iodine water

Students must name the substance not give chemical formula. Besides that, the sol ution must be present. Correct answer : Acidified potassium manganate(VII) solution // Acidified potassium dichromate(VI) solution // Chlorine water.

Example 11 What is the function of dilute sulphuric acid? 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 12 State the observation at carbon electrode X. Q5 (b) (i) Wrong answer : solution turns yellow.

For all the observation (colour changes), students must state the colour of the solution before reaction 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 13 State the observation at carbon electrode 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 14 What 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.

Common Mistakes for SPM 2010 Chemistry Paper 2 Section B (based on Johor State Trial SPM 2010 Paper)

SPM question Paper 2 Section B  – essay questions (Question 7 & 8 ) (Choose 1 to answer) consist of  20 marks in total. In this section, students need to answer any 1 question from this section. There are some important rules or answering techniques that students need to follow. We will be discussing these points by using 2010 Johor state trial paper 2 (Section B  – Question number 7 and 8). 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 a complete 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. 

Ionic bond between magnesium atom and chlorine atom. 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. Compound formed in (b) (i) can conduct electricity in the molten state while compound formed in (b) (ii) cannot conduct electricity in any state. 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 CCl4 need less energy to energy to overcome the overcome the forces. strong electrostatic force  / fixed crystal lattice structure. 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 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 the energy released if 6.9 grams of ethanol is burnt completely in air.

Wrong answer:

Number of mole of ethanol = 6.9 / 46 = 0.15 -1 0.15 mole will form 0.15 x 715 = 107.25 kJ mol 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

Common Mistakes for SPM 2010 Chemistry Paper 2 Section C (based on Johor State Trial SPM 2010 Paper) Students need to answer any one question from this section C (experimental essay). The SPM

questions in Paper 2 Section C (Question 9 & 10) consist of 20 marks in total. The Johor state SPM 2010 trial paper 2 (Section C – Question number 9 and 10) is used in the following discussion. 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.

i.e. “By using a suitable diagram , explain a laboratory experiment to determine …” I would recommend that even the question not stated this statement, it is better for the students to draw the diagram because it will help you in remembering the important apparatus and material which is being used in the experiment. Besides that, you need to label (apparatus and material) the experimental diagram. 2) What are the techniques in writing these procedures?

Each sentence or procedure step must have this combination to form a sentence. Subject (material or apparatus) + verb + object (material or apparatus). 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

Using a suitable example, describe a laboratory experiment to determine the empirical formula of an oxide of a reactive metal. Your explanation should include: • procedure of the experiment… Q9 (c) (iii) Correct answer candidate A (passive form –  past perfect tense): 1. 5 cm of magnesium ribbon was cleaned with sandpaper to remove the oxide layer. 2. An empty crucible and its lid were weighed using electronic balance and its mass was recorded. 3. The coiled magnesium ribbon was placed in the crucible. 4. The crucible, crucible lid and magnesium ribbon were weighed and its mass was recorded. 5. …

Correct answer candidate B (passive form –  present perfect tense): 1. 5 cm of magnesium ribbon is cleaned with sandpaper to remove the oxide layer. 2. An empty crucible and its lid are weighed using electronic balance and its mass was recorded.

3. The coiled magnesium ribbon is placed in the crucible. 4. The crucible, crucible lid and magnesium ribbon are weighed and its mass is recorded 5. …

But for those students who are very weak in English language , I would recommend you to write in active form sentence (present tense). Correct answer candidate C (active form):

1. 2. 3. 4. 5. 6.

Clean 5 cm magnesium ribbon with sandpaper. Coil magnesium ribbon. Weigh an empty crucible with its lid. Record the reading. Place the magnesium in the crucible and weigh again. Record the reading.

4) Is it a compulsory to give example for the experiment? Yes. Students need to give an example of the material. Example 2

Using a suitable example, describe a laboratory experiment to determine the empirical formula of an oxide of a reactive metal.  

Procedure of the experiment ( Prosedur bagi eksperimen) Tabulation of data ( Penjadualan data ) Q9 (c) (iii)

Wrong answer:

1. 5cm metal ribbon was cleaned with sandpaper. 2. … Description Crucible + lid Crucible + lid + metal Crucible + lid + metal oxide

Mass (g)

Correct answer:

1. 5 cm of  magnesium ribbon was cleaned with sandpaper. 2. … Description Crucible + lid Crucible + lid + magnesium Crucible + lid + magnesium oxide

Mass (g)

(Students do not need to include the value of mass unless it is given in the question.)