Teknik Menjawab Kimia Spm p6g63

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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(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. 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.

4. 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 ed 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 ed.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

CORRECT Excess copper(II) oxide

Filter Paper

Filter funnel

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

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WRONG

CORRECT

8.Wire gauge should not be used

Clay pipe triangle

Wire gauge

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Heat

Program Intervensi PPSMI 2007

Heat

14

WRONG

CORRECT

9.Delivery tube not inserted inside lime water

Heat 1/5/2013

Lime water

Heat

Lime water 15

WRONG

CORRECT

Direction of water flow is not correct

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WRONG

CORRECT

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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WRONG Thistle funnel

Dilute hydrocloric acid

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Thistle funnel must be immersed in solution

CORRECT Thistle funnel

Dilute Hydrocloric acid

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WRONG

CORRECT

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 cm3 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(NO3)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 – 2.0 mol dm-3) 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.

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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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Thank You

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