Teknik Menjawab Kimia SPM

TECHNIQUE OF ANSWERING SPM CHEMISTRY

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MISTAKES normally made by students

I.Writing equations II Describing colours III Mistakes in drawing diagrams IV Calculations V Chemical Tests VI Mistakes in experiment-based questions VII Incomplete/Inaccurate statements or  phrases. 1/5/2013

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MISTAKES normally made by students

I.Writing equations II Describing colours III Mistakes in drawing diagrams IV Calculations V Chemical Tests VI Mistakes in experiment-based questions VII Incomplete/Inaccurate statements or  phrases. 1/5/2013

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(I)Writing Equations 1. Equation not balanced Eg: Na + O2 Na2O 2. Cannot differentiate between • Ionic equations : Zn + 2H+ Zn2+ + H2 • Half equations : 2H+ + 2e H2 Zn Zn2+ + 2e • Chemical equations (complete equations) 2HCl + Zn ZnCl2 + H2 1/5/2013

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Writing Equations 3. Do not write WORD EQUATIONS

4. Do not use symbol or formulae in answering structured and essay questions. (except for ions or in diagrams) 5. Wrong half -equation. -equation . Eg: 4OH- - 4e  O2 + 2H2O

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(II)Describing Colours 1. Not able to state the colour of  of chemical/reagent accurately or correctly 2. Describing water or solution which is colourless ,as clear 

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Describing Colours 3. Fail to mention the initial colour when there is a colour change Eg : A pink coloured solution is produced Correct : The colourless solution turns pink.

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Change in colour of bromine water  Eg(1): bromine water is bleached Correct : Brown bromine water is decolourised eg(2): Copper is formed at the cathode Correct : A brown deposit is formed at the cathode

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(III)Mistakes in drawing diagrams 1.

Drawing the stopper below the mouth level of the test tube. Eg WRONG

Diagram A 1/5/2013

CORRECT

Diagram B 7

2. No ‘Heat’ beside the arrow CORRECT

WRONG  No ‘Heat’ label

Crucible Crucible

Heat

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3. Gas passed through and excess gas must be allowed to escape WRONG No gas outlet

Heat

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CORRECT

Heat

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4. To represent solution drawing ‘dash’ lines WRONG

CORRECT

No indication of solution

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5. Drawing a battery in the circuit of a chemical cell WRONG

CORRECT

Symbol for battery given in the diagram

Copper(II) sulphate solution 1/5/2013

Copper(II) sulphate solution 11

6. Certain apparatus not supported.Eg Burettes not attached to clamp/retort or test/combustion tubes floating while being heated WRONG

CORRECT Boiling Tube

Boiling Tube

Lead(II) Carbonate

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Lead(II) Carbonate

Heat

Lime water

Heat

Lime water

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WRONG

7. Diagram not labelled

Excess copper(II) oxide

Filter Paper

Filter funnel

Filterate (Copper(II) sulphate solution) 1/5/2013

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WRONG 8.Wire gauge should not be used

Clay pipe triangle

Wire gauge

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Heat

Program Intervensi PPSMI 2007

Heat

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WRONG 9.Delivery tube not inserted inside lime water

Heat 1/5/2013

Lime water

Heat

Lime water 15

WRONG Direction of water flow is not correct

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WRONG e e

Copper(II) sulphate solution

Copper(II) sulphate solution

Direction of electron flow shown is not right 1/5/2013

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Thistle funnel

Dilute hydrocloric acid

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Thistle funnel must be immersed in solution

Thistle funnel

Dilute Hydrocloric acid

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WRONG

All electron shells must be shown

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(IV)Calculations 1.

Steps not shown

6.62 g of lead(II) nitrate is dissolved in 500 cm 3 of  distilled water. Calculate the concentration of the solution formed.  Incorrect: Concentration = 0.04 mol dm -3 Correct : Relative formula mass of lead(II) nitrate,Pb(NO 3)2 = 207 + 2(14 + 48) = 331  Number of mole of lead(II) nitrate = 6.62/331 =0.02 Concentration = 0.02/0.5 = 0.04 mol dm -3 1/5/2013

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(IV)Calculations 2. 1/Time (Rate of reaction) should be given to 3 decimal place. 3. Units not shown or wrong unit given Contoh:

wrong ∆H = a kJ mol -1 1/5/2013

correct ∆H = +/- a kJ mol -1 21

(V)Chemical Tests 1. Add sodium hydroxide into a test tube to test for Fe2+ ions. 2. Correct : Add sodium hydroxide  solution into a test tube until excess. Green precipitate which cannot  dissolve in excess is formed.

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2. Incomplete method of testing for a gas . Suggest a test for the gas given off when sodium nitrate is heated 

 Incorrect Answer : Test with a glowing splinter   Incorrect Answer: Insert a glowing splinter into the test tube containing the gas Correct Answer : Insert a glowing splinter into the test tube containing the gas.The gas relights/rekindles the glowing splinter. 1/5/2013

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(VI)Mistakes in experiment-based questions 1. Leaving out the key action words/phrase:  Add something to something else Stir evenly Mix together more than two substances Heat gently/warm Heat strongly 1/5/2013

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2. Not stating the quantities used  •For solutions a certain volume(based  on apparatus used) and molarity(0.1  – -3 2.0 mol dm  ) should be mention •For change in temperature, a certain range/increase/decrease in temperature should be mentioned  •For solids a certain mass should be mentioned, or whether it should be used in excess 1/5/2013

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3. Describing an observation Eg : Hydrogen gas is released Correct : Effervescence or  gas bubbles released 4. Drawing graphs: The axes not labelled and/or units not mention 1/5/2013

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5. Electrochemical Series confused  with Reactivity Series Eg.Zinc can displace copper from copper(II) sulphate solution because zinc is higher than copper in the Reactivity Series(should be Electrochemical Series)

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6. Not stating the state/size of substance eg. Not stating aqueus potasium iodide or  potassium iodide solution Not stating magnesium powder where size of reactant matters

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7.Not knowing the meaning of compare and contrast (differentiate) Compare: find the similarities and  differences between 2 or more things Contrast : to find only the differences between 2 things

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7(b) Eg : Not knowing the meaning of  compare and contrast: Ques: Compare the properties of ionic and  covalent compound  Students Ans: ionic compounds have high boiling point/melting point, can dissolve in water and conduct electricity in molten or aqueous form. (No mention about covalent compound) 1/5/2013

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Incomplete/Inaccurrate statement/phrases 1.Sodium donates electron. Correct :One sodium atom donates one electron

2.Stable electron arrangement Correct : Stable octet arrangement of electrons

3.Rate of reaction described as fast or slow Correct:Fast reaction  – high rate Slow reaction  – low rate 1/5/2013

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4.Rate of reaction getting slower  Correct : Rate of reaction decreases 5.The smaller the size of substance the bigger the surface area Correct :

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The smaller the size of the substance the bigger is the total surface area. 32

6.An ionic compound can conduct electricity Correct: An ionic compound can conduct electricity in the molten state/aqueous solution

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7.Relative atomic mass of an element is the number of times an atom of an element is heavier than hydrogen. Correct : Relative atomic mass of an element is

the number of times an atom of an element is heavier than one atom of hydrogen.

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8. A Hydrocarbon is a compound that contains carbon and hydrogen. Correct : A Hydrocarbon is a compound that contains carbon and  hydrogen only . 1/5/2013

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9. A base is a substance that contains oxide/hydroxide ions Correct : A base is a substance that produces hydroxide ions when dissolved in water  1/5/2013

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10. An acid is a substance that contains hydrogen ions. Correct  : An acid is a substance that produces hydrogen ions when dissolved in water. 1/5/2013

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11. Calsium is situated in Period IV

Correct : Calsium is situated in Period 4

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12. A chloride ion has three electron shells Correct : A chloride ion has

three shells filled with electrons.

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13. When the temperature is increased, the number of collisions also increases Correct : When the temperature is increased, the number of collisions between the named particles also increases 1/5/2013

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14. The oxidation nombor of  Fe 2+ ion changes/ increase Correct : The oxidation

nombor of iron in Fe 2+ ion changes/ increase from +2 to +3

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15. A polystyrene cup is used to prevent heat loss. Correct : A polystyrene cup is used to reduce heat loss.

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16. Attractive forces between molecules are small /lower/higher Correct Ans : Attractive forces between  molecules are weak / strong 17. Copper attracted to to the cathode Correct Ans :Copper ions attracted to to  the cathode 18. The ions in the electrolyte can move Correct Ans :The ions in the electrolyte  can move freely 1/5/2013

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