Wednesday, November 3, 2010

Examination Tips - SPM Chemistry


Etems Intervention Programme ; 
Materials For Form Five Students
 *courtesy of JPN Perak

Contents
·         List of important command words, with examples
·         Answering Techniques  and common mistakes made by candidates
·         


List of important command words, with examples
The words used in examination questions often indicate what sort of answers  are expected.
1. Define (Takrifkan)
     This means you are only required to write a concise statement to say what something is or means
     Example: Define relative atomic mass
     Suggested Answer:  It is the average mass of an atom of an element compared with 1/12th of the mass of a carbon-12 atom

2. State (Nyatakan)
     This means a short, concise answer is expected, without explanation
     Example:  State one  commercial use of aluminium
     Suggested Answer:  It is used to manufacture soft drink cans

3. List ( Senaraikan)
    This means you are to give a number of points in a list. Each point might only be a single word or a short phrase or sentence
    Example:  List three pollutants that are produced by car engines.
    Suggested Answer:  Carbon dioxide
                      Nitrogen dioxide
                      Unburnt fuel /soot

4. Explain (Jelaskan/huraikan)
    This usually means some reference to chemical theory
    Example: Explain why 2.0 mol/dm-3 hydrochloric acid reacts more quickly with solid calcium carbonate than 1.0 mol/dm3 acid
  Suggested Answer: For the 2.0 mol/dm-3 acid, there are more hydrogen ions per unit volume of acid and so collide more frequently with calcium carbonate (your mention of ‘more frequent collisions’ is the theory)


5. Describe (Huraikan)
     Writing in full and systemically, what has been carried out, observed or deduced and with diagram of apparatus used.
     Example: Describe how ethanol can be produced by fermentation in the laboratory.
     Suggested Answer: Your answer should contain the following :
·         Simple diagram of the apparatus
·         One or two sentences saying what you should do, including:
·         Materials used (ie sugar, yeast, water )
·         Conditions (ie leave in a warm place  for a few days; plug the flask so that air cannot get in )
·         Equation (if you know it ) or at least mention that glucose decomposes into ethanol and carbon dioxide.
(How much you write would depend on the marks allocated for the question)

6. Predict or deduce (Ramalkan)
    This means you are to deduce an answer from information in the question or from anearlier answer. You are not expected to produce an answer from memory.
    Example : Predict the physical state of octane, which has 8 carbon atoms
     (You are given the boiling points of all the alkanes with 1-7 carbons atoms)
    Sugested Answer: A liquid at room temperature ( From the given boiling points of the other alkanes, you can predict that octane will have a higher boiling point and will thus be a liquid at room temperature)

7. Suggest (Cadangkan)
     This means that you are not expected to know the correct answer but you are supposed to make a logical deduction from the information given in the question or from your chemical knowledge. Your answer may not be true, but it is correct if what you say is sensible from what you might reasonably be expected to know
    Example : From your knowledge of Group VII, suggest two physical properties of astatine at the bottom of the Group
    Suggested Answer: Astatine would be a black solid which does not conduct electricity, because all the Group VII elements are non-metals and the elements become darker down the Group, with increasing density. (This would be the logical answer even though no one has ever been able to obtain a lump of astatine to see what it looks like or to find out if it really does not conduct electricity!

8. Calculate (Hitungkan)
    This means a numerical answer is expected and the working given in full/all  the steps shown
    Example : In an experiment, 1.30 g of zinc powder and 200 cm3 of 0.2 mol/dm3 sulphuric acid were reacted together.
(a)    Calculate the number of moles of zinc in 1.30 g       [1]
(b)   Calculate the number of moles of sulphuric acid in the solution   [2]
Suggested Answer: (a) moles of zinc = 1.3/65 = 0.02 mole
                                    (b) 200/1000  x  0.2 = 0.04 mol




 9. Determine (Tentukan)
     This usually means the answer cannot be measured directly but is obtained by calculation or perhaps, by taking a reading from graph. Normally a numerical answer is expected

10. Sketch (Lakarkan)
      This is often applied to graphs. It means that only the correct shape and approximate position of the graph is expected. It might mean you need to add one or two numbers to make the position clear. (Plotting a graph requires actual/experimental readings)

      If you are asked to sketch a diagram then only a freehand drawing is expected. It can be quite rough but it must be clear what is shown and any important details must be clear. For example, if a rubber bung is supposed to seal a flask, this should be obvious in your sketch; it would be wrong to leave a gap between the flask and the bung.
    In a sketch of apparatus, the proportions must be roughly correct.Eg a test tube should not be drawn  larger than a conical flask.  


Some command words in Paper 3

(1) To differentiate between ‘products’ and ‘observation’
      Observation: describe what is actually seen/observed/smelled
      Products: names in full, not formula
·         Examples of observation
(i) Solid or precipitate formed.Colour must be mentioned
(ii)Whether solid in (i) is soluble or insoluble in excess of named reagent
(iii) If gas, colour must be stated( if relevant) or chemical test described followed by the result
(iv) change in colour : must state initial and the final colours

·         Common mistakes in describing observations

Inaccurate/Incorrect
Correct
Clear (solution)
Colourless (solution)
No reaction seen
No change seen
Hydrogen gas released
Colourless  gas given out
Movement shown by ammeter
Deflection of ammeter needle
Purple colour disappears or purple solution bleached
Purple solution decolourised
Product of electrolysis  at the cathode:
Brown precipitate seen

Brown deposit/solid seen
Red litmus paper becomes blue litmus paper
Moist red litmus paper turns blue

·         Examples of ‘Action Words’ in Chemical Tests

(i)  Add one reagent to another in a named container
(ii) Mix together 2 reagents /chemicals in named container
(iii) For gases : Channel/pass a gas through eg a combustion tube (excess will escape)
                           Bubble the gas into eg lime water  (no excess coming out)                      
(iv) Insert glowing splint into a test tube containing ----------
(v)Place/Put lighted splint near the mouth of a test tube containing --------
            (vi) Titiskan / add, drop by drop or a little at a time.  

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