Thursday, September 24, 2009

List of important command words, with examples

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.

  1. Calculate the number of moles of zinc in 1.30 g [1]
  2. 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



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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Periodic Table