Teknik menjawab kimia

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Page 1: Teknik menjawab kimia

04/12/23 Program Intervensi PPSMI 2007 1

TECHNIQUETECHNIQUEOFOF

ANSWERING SPM ANSWERING SPM CHEMISTRY CHEMISTRY

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MISTAKESMISTAKESnormally made by studentsnormally made by students

I.Writing equationsII Describing coloursIII Mistakes in drawing diagramsIV Calculations V Chemical TestsVI Mistakes in experiment-based

questionsVII Incomplete/Inaccurate statements or

phrases.

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1. Equation not balanced Eg: Na + O2 Na2O2. 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

(I)Writing Equations(I)Writing Equations

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Writing EquationsWriting 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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1. Not able to state the colour of of chemical/reagent accurately or correctly

2. Describing water or solution which is colourless ,as clear

(II)Describing Colours(II)Describing Colours

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Describing Colours Describing Colours

3. Fail to mention the initial colour when there is a colour change

Eg: A pink coloured solution is producedCorrect: The colourless solution turns pink.

4. Change in colour of bromine waterEg(1): bromine water is bleachedCorrect: Brown bromine water is

decolourised eg(2): Copper is formed at the cathodeCorrect: A brown deposit is formed at the

cathode

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

Diagram A Diagram B

(III)Mistakes(III)Mistakesin drawing diagramsin drawing diagrams

WRONG CORRECTWRONG CORRECT

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2. No ‘Heat’ beside the arrowWRONGWRONG CORRECTCORRECT

HeatHeat

No ‘Heat’ No ‘Heat’ labellabel

CrucibleCrucibleCrucibleCrucible

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3. Gas passed through and excess gas must be allowed to escape

WRONGWRONGNo gas outletNo gas outlet

HeatHeatHeatHeat

CORRECTCORRECT

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4. To represent solution drawing ‘dash’ lines

WRONGWRONG CORRECTCORRECT

No indication of solutionNo indication of solution

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

WRONGWRONG CORRECTCORRECTSymbol for battery given in the diagramSymbol for battery given in the diagram

Copper(II) sulphate Copper(II) sulphate solutionsolution

Copper(II) sulphate Copper(II) sulphate solutionsolution

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

WRONGWRONG CORRECTCORRECT

Boiling TubeBoiling Tube

Lead(II)Lead(II)CarbonateCarbonate

HeatHeatLime waterLime water

Boiling TubeBoiling Tube

Lead(II)Lead(II)CarbonateCarbonate

HeatHeatLime waterLime water

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WRONG CORRECT

7. 7. Diagram not labelledDiagram not labelledExcess Excess copper(II) oxidecopper(II) oxide Filter PaperFilter Paper

Filter funnelFilter funnel

Filterate Filterate (Copper(II) sulphate (Copper(II) sulphate solution)solution)

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WRONG CORRECT

8.8.Wire gauge Wire gauge should not be usedshould not be used

Wire Wire gaugegauge

HeatHeat

Clay pipe Clay pipe triangletriangle

HeatHeat

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WRONG CORRECT

99.Delivery tube not .Delivery tube not inserted inside lime waterinserted inside lime water

HeatHeat Lime waterLime water HeatHeat Lime waterLime water

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WRONG CORRECTDirection of water flow Direction of water flow is not correctis not correct

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Direction of electron flow shown is not right

WRONG CORRECT

ee ee

Copper(II) sulphate Copper(II) sulphate solutionsolution

Copper(II) sulphate Copper(II) sulphate solutionsolution

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Thistle funnel must be immersed in solution

WRONG CORRECTThistle funnelThistle funnel

Dilute Dilute Hydrocloric acidHydrocloric acid

Thistle funnelThistle funnel

Dilute Dilute hydrocloric acidhydrocloric acid

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WRONG CORRECT

All electron shells must be shownAll electron shells must be shown

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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

1.1. Steps not shownSteps not shown(IV)Calculations(IV)Calculations

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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 givenContoh:

wrong correct

∆H = a kJ mol -1 ∆H = +/- a kJ mol -1

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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.

(V)Chemical Tests

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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.

2.2. Incomplete method of testing for a gasIncomplete method of testing for a gas..

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1. Leaving out the key action words/phrase:

Add something to something elseStir evenlyMix together more than two

substancesHeat gently/warmHeat strongly

(VI)Mistakes in experiment-based questions

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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

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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

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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

.Calon hanya memberikan sifat fizikal sebatian ionik sahaja.

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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)

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1.Sodium donates electron.Correct :One sodium atom donates one electron

2.Stable electron arrangementCorrect: Stable octet arrangement of electrons

3.Rate of reaction described as fast or slow Correct:Fast reaction – high rate

Slow reaction – low rate

Incomplete/Inaccurrate Incomplete/Inaccurrate statement/phrasesstatement/phrases

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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 areaCorrect : The smaller the size of the

substance the bigger is the total surface area.

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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

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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.

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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

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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 cathode18. The ions in the electrolyte can move Correct Ans :The ions in the electrolyte

can move freely

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Guidelines on answering questions in chemistry paper 2

• 1 General• (a) Read all questions carefully and circle all

important key words• (b) Answers can be short but they must be precise

and complete• © The space provided for your answer gives an

indication as to ‘how long’ the answer should be• (d) Always look at the marks alloted for each

question as a guide to how many points you should give

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Answers must be precise

• eg. State the conversion of energy that occurs during the electrolysis

• Answer: The energy conversion that occurs during electrolysis is from electrical to chemical energy or from electrical energy to chemical energy

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Answers must relate to the needs of the questions

• Example• State the observation(s)• (a)Incorrect observation: chlorine gas released• Correct observation: Efferverscence/ gas

bubbles released/ light greenish yellow gas given out.

• (b) Incorrect observation: copper formed• Correct observation: brown solid deposited • © Incorrect observation :Deflection of the

galvanometer• Correct observation: Deflection of the

galvanometer needle

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Use the correct terminology

• 1)If the name of a person is used as unit or a chemical process, it must be in capital letter

• Do not use the abbreviation such as ESC,RAM,RMM

• 2)Common inaccurate or incomplete answers• Wrong: Purple solution disappears• Correct: Purple solution decolourised

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Use the correct terminology• Wrong observation: No reaction• Correct observation: No change• Wrong: rate of reaction is faster or

slower• Correct: rate of reaction is higher or

lower• Wrong: zinc donates two electrons• Correct: zinc atom donates two

electrons

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Use the correct terminology• Wrong: copper molecule • Correct: copper atom• Wrong: bromine ion • Correct: bromide ion• Wrong: H+ ion increase• Correct: Concentration or number of moles of

hydrogen ion increases• Wrong: Electrons flow from zinc metal to

copper metal • Correct: Electrons flow from zinc metal to

copper metal through the wire

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Use the correct terminology• Wrong:Forces of attraction are weak • Correct: Intermolecular forces of attraction

are weak• Wrong:Soap consist of two parts • Correct: Soap anion consist of two parts• Wrong: Position of zinc is above copper • Correct: Position of zinc is above copper in the

electrochemical series or zinc is more electropositive than copper

• WrongReagent to verify iodine – starch • Correct: Starch solution• Wrong: Colour of water is clear/ white• Correct: Colourless

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Describing chemical test• Description must have• 1) correct reagent 2) procedure3) expected observation• You must state how you would carry out the test using the

reagent and what is the observation to verify the identity of the substance

• Eg Name gas Y and describe a method to verify its identity• Wrong: Test with lime water• Correct: Pass the gas into lime water. Lime water turns

milky/chalky verifying the gas is carbon dioxide.

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Stating the correct changes in observation or state

• You must state the change from the initial colour or state to the final colour or state

• Wrong: Moist litmus paper turns red• Correct: Moist litmus paper turns from blue to

red• Wrong:Oxidation number changes to +2• Correct: Oxidation number changes from 0 to

+2

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Write clearly the working of the calculation

• Marks are given for working and hence they must be written clearly

• Unit must be correct• Wrong: 16/64 = 0.25 0.25 x 32= 8g• Correct:Number of mole copper = 16/64• = 0.25 mol• Mass of oxygen gas = 0.25 x 32 = 8g

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Plotting the graph• Both axes must be labelled with the correct variable

and unit(if any) must be written• If no scale is given, use the appropriate scale so that

the graph drawn covers at least half of the page• Points plotted must be correct• Draw the best smooth straight line or curve• If the value of the variable needs to be obtained

from the graph, you must show how this value is obtained by marking on the graph

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Drawing the set-up apparatus

• Set-up apparatus drawn must be functional• Materials and main apparatus must be

labelled• Areas representing solids, liquids and

solutions must be shaded• A two dimensional diagram should be drawn

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Guidelines on answering Paper 2Essay question

• A )General• Read all questions carefully• Always note the marks alloted for each part of the

question. This will be an indication as to how many points or facts you need to give

• Whenever possible, substantiate your answer with labelled diagrams or equations

• Answer according to the instruction of the question. Marks are alloted for each instruction

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Answering Paper 2 Essay question

• B) Why students lose marks• 1. Did not give enough facts or points or

incomplete facts• 2 Did not give the correct conditions of the

experiment• 3 Did not write chemical equation• 4 Wrong words or terms used

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Suggested format when answering paper 2 question involving experiment

• Item to be written• (a) title/aim (b) Apparatus and materials• © Set-up of apparatus diagram-

functional,labelled• (d) Procedure- (i)You must describe how you

measure and pour the chemical substances into appropriate containers

• (ii) Values of concentration and volume of the solution must be stated

• (iii) Steps taken while carrying our the experiment must be written in the correct order

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Paper 2 involving experiment• (iv) Write “ readings or measurements are recorded”• (v) You must ensure that the chemical substances

you choose are correct and will react accordingly to give the desired result –giving the correct products

• (vi) Chemical substances can be written in words or chemical formulae. If chemical formuale are used, they must be correct

• The physical state of the chemical substances must also be stated. Example solution or solid or gas, powdered or pieces of ribbon, acidified or neutral etc

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Essay questions involving experiment

• (d) Observation or theory or explanation• (i) Answer according to the needs of the

experiment. If certain facts are not asked, you can write briefly.

• (ii) Include chemical equation or half equation or graph in your answer to make your answer easily understood.

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Essay questions paper 2 involving experiment

• (e) Tabulation of data / result• The readings normally need to be presented

in a table. Your table must have the correct headings and units. Values must be give for the manipulated variable.Symbols can be used for the responding variable

Time(s) 30 60 90 120Temperature (oC)

t1 t2 t3 t4

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Essay Questions involving experiment

• (f) Calculation• If real values are not given, you can use

unknown such as x,y,z in your calculations• All steps must be clearly shown and units

must be written• (g) Conclusion• A conclusion must be written based on the

aim of the experiment

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Guideline on answering questions Paper 3

• 1) Scientific skills ( assessed in structed question- total marks :33)

• (a) Observing (b) classifying• © Measuring and using numbers• (d)inferring (e) predicting • (f) communicating• (g) Using space-time relationship• (h) Intepreting data• (i) Defining operationally• (j) Controlling variables• (k) Hypothesizing

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Techniques on answering questions in paper 3

• (a) classifing- draw a table with a ruler, every column must have a correct heading and units must be written (if any)

• (b) observing- Write what you see, hear, feel, taste or smell

• © making inference- State the appropriate inference that explains the observation/results. You must give an inference that corresponds with the observation/results

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Technique paper 3• (d) predicting- You need to analyse all the

information given(observations, previous experiences or data that can be trusted) and hence make a forecast(prediction) according to the need of the question

• (e) measuring and using numbers- You must write the value of the measurement according to the accuracy of the apparatus used. All the values written must be uniform and have the correct unit.

• Ruler- one decimal place eg.9.6 cm• Measuring cylinder, pipette 25cm3 ,stop watch,

thermometer ,– one decimal place• Burette 50cm3 two decimal places, the second

decimal place must end with 0 or 5

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Paper 3- Question 3(17 marks) involving planning an experiment

• 1)Answer according to the need of the question. Write the report according to the headings required in the question.You must write the headings and not the question number or part question

• 2)Technique • (a) Aim of the experiment- Read the question carefully and

the aim for the experiment is clearly stated in the question. The aim must be written accurately

• (b) Problem statement- the problem statement must be a question ending with a question mark’?’ The problem statement should used certain key word such as ‘WHATt” , ‘HOW’. The problem statement need to be accurate and complete

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Question 3-Paper 3Technique

• © Hypothesis- The statement usually correlated the manipulated variable and the responding variable. The manipulated variable must be written in front of the statement and followed by the responding variable. Need to state the ‘direction-right one’ of change for both the variable

• (d) All variables• Manipulated variable: Materials that we use and change in

the experiment• Responding variable: Measurement(using apparatus, through

observation or product of the reaction) that is recorded for each material that we change in the experiment

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Question 3-paper3technique

• (e) List of apparatus and materials• State the name of all materials(including its concentration)

and all apparatus• A labelled diagram of the set-up apparatus may complement

the list• (f) Procedure- • Voume and concentration must be written. State the quantity

of the material used. Do not write ‘about 3 gram”. The steps in the procedure must be in order. Use passive sentences.

• (g) Tabulation of data• Must draw table using a ruler. Every column must have a

heading and its unit (if any). Manipulated variable must be on the left side of the table and responding variable on the right side.

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