Sunday, August 7, 2011

Common Mistakes for SPM Chemistry Paper 2 Section C

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… (Dengan menggunakan contoh yang sesuai, huraikan suatu experimen di makmal untuk menentukan formula empiric bagi suatu oksida logam reaktif. Penerangan anda mestilah meliputi: • prosedur bagi eksperimen… ) 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.

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

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. Clean 5 cm magnesium ribbon with sandpaper.
  2. Coil magnesium ribbon.
  3. Weigh an empty crucible with its lid.
  4. Record the reading.
  5. Place the magnesium in the crucible and weigh again.
  6. 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. (Dengan menggunakan contoh yang sesuai, huraikan suatu experimen di makmal untuk menentukan formula empiric bagi suatu oksida logam reaktif.)

  • 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.
DescriptionMass (g)
Crucible + lid
Crucible + lid + metal
Crucible + lid + metal oxide

Correct answer:

  1. 5 cm of magnesium ribbon was cleaned with sandpaper.
DescriptionMass (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.)

Best regards,

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