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MRSM PENGKALAN CHEPA CHEMISTRY UNIT 2013. GUIDELINES FOR ANSWERING PAPER 3. Structure Question NO 1 or NO 2 is to test the mastery of 11 Scientific Skills 1. Observing 2. Classifying 3. Inferring 4. Measuring (burette , stopwatch, thermometer, voltmeter)

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mrsm pengkalan chepa chemistry unit 2013
MRSM PENGKALAN CHEPACHEMISTRY UNIT2013

GUIDELINES FOR ANSWERING PAPER 3

slide2

Structure Question NO 1 or NO 2 is to test the mastery of 11 Scientific Skills

1. Observing 2. Classifying 3. Inferring

4. Measuring (burette , stopwatch, thermometer, voltmeter)

5. Predicting 6. Communicating( e.g construct table and draw graph)

7. Space-Time Relationship

8. Interpreting Data 9. Defining Operationally 10. Controlling Variables 11. Hypothesizing

slide3

Operational definition is a statement that contains:

1. what you do/procedure

2. what you see/observation

Examples

1. State OD for coagulation of latex

When acid is added into latex,

white solid is formed- correct

(When acid is added into latex, latex coagulated.- wrong)

slide4

2. State Op Deffor rate of reaction in this experiment

When the higher concentration sodium thiosulphate solution is added into sulphuric acid,

time taken for `X~ mark to disappear from sight is shorter.

slide5

3. State Op Deffor rusting of iron

When iron nail is coiled with copper and immersed into jelly mixed with potassium

hexacyanoferrate(III) and phenolphthalein solution,

blue spot/colouration is formed.

slide6

More examples on Operational definition

What you do - What is observed

1. Rusting of iron -

When an iron nail coiled with a less electropositive metal is immersed in hot agar-agar added with potassium hexacyanoferrate (III) solution,

blue spots are formed

slide7

More examples on Operational definition

What you do - What is observed

2. Coagulation of latex -

When acid is added to latex

White solid is formed

slide8

3. Reactivity of Group 1 elements

When a metal which is lower in Group 1 is put in a basin half filled with water

brighter flame is formed

4. Precipitation of silver chloride

When silver nitrate solution is added to sodium chloride solution

White solid is formed

slide9

3. 5. Voltaic cell

When two different metals are dipped into an electrolyte

The needle of the voltmeter deflects//Voltmeter shows a reading

slide10

More examples on Operational definition

What you do What is observed

6. An acid

When a blue litmus paper is dipped into a substance which is dissolved in water,

blue litmus paper turns red

slide11

More examples on Operational definition

What you do What is observed

7. Heat of combustion

When 1 mol of fuel is burnt in excess oxygen

Temperature rises//Thermometer reading increases

slide12

More examples on Operational definition

What you do What is observed

8. Hardness of alloy

When a weight is dropped on a steel ball bearing taped on an alloy block

diameter of dent formed is smaller

slide13

Hypothesis: ( early conclusion to aim of exp)

  • Statement that relates the MV followed by responding variable with direction.
  • Example:
  • The higher temperature of the reactant the higher the rate of reaction – 3 marks
  • 2. Hexenedecolourised brown bromine water but hexane does not
slide14

Hypothesis: ( early conclusion to aim of exp)

Statement that relates the MV followed by RV with direction.

Example:

3. When acid is added into latex, latex coagulates, when ammonia is added into latex, latex cannot coagulates

slide16

When hexene is added to bromine water, brown colour decolorized, but when hexane is added to bromine water, brown bromine not changed

slide18

When acid is added to latex, coagulation of latex occurs, but when ammonia solution is added to latex, NO coagulation occur

slide21

1 Diagram 1 shows three sets, Set I, Set II and Set III, of the apparatus set-up for an experiment to investigate the effect of ethanoic acid and ammonia solution on the coagulation of latex.

slide22

Latex + ethanoic acid

Latex coagulate

Latex + not coagulate

Latex + ammonia

Latex only

Latex coagulate

slide23

(a) State one hypothesis based on Set I and Set II.

Acid coagulate latex

while

alkali does not coagulate

the latex

slide24

(b) Record the time taken for the latex to coagulate in Set 1 and Set III.

Set I : 5 minutes // 300 s

Set III: 6 hours // 60 minutes// 21600 s

slide25

(c) Construct a table to record the time taken for coagulation in Set I and Set III.

slide26

(d) State one observation that can be obtained from each set of this experiment.

Set I : Latex coagulates

/ A solid lump is formed

Set II : Latex does not coagulate

/ No change / Liquid

Set III : Latex coagulates

/ A solid lump is formed

slide27

(e) State the operational definition for the coagulation of latex.

When acid is added to latex,

it becomes solid

slide28

Ethanoic acid / Acid/(Ammonia solution) / Alkali

(f)

Manipulated variable:

Responding variable :

Constant variable :

Coagulate //Time taken for coagulation

Vol of latex / acid / (ammonia solution)

/ alkali // latex /temp

slide29

(g) (i) Set II after 2:00 p.m. What observation can be made about the latex?

Latex coagulates // Latex becomes solid/(semi-solid) //Latex is solidified

slide30

bacteria in air reacts with latex to produce

lactic acid ( H +)

(ii) Explain the answer in l(g) (i).

Hydrogen ions (H+ ) neutralise OH-ions

in ammonia solution

Hydrogen ions (H+ ) neutralised the negative charge of protein membrane, collisions of rubber particles occur, rubber molecules clump

slide31

Bacteria in air reacts with latex to produce lactic acid / H+

  • Explain why latex can coagulate without acid in Set III.

These H+neutralise the negatively charged on the protein membrane of latex particles

Latex particles no longer repel each other, so the particles collide, rubber molecules clump

slide32

i) (i) Explain why the latex in Set I coagulates faster than the latex in Set III.

The concentration of hydrogen ion, H+ in Set I is higher than in set III

In set I , H+ produced, neutralise

the negatively charged on the protein membrane faster than in set III

slide33

(ii) The following is a list of chemical substances

  • Nitric acid
  • Sodium hydroxide
  • Methanoic acid
  • Potassium hydroxide

Classify these substances into substances that can coagulate latex and substance that cannot coagulate latex.

slide34

Potassium hydroxide

Sodium hydroxide

Nitric acid

Methanoic acid

exp 1 electrolysis cuso 4 using c as electrode exp 2 electrolysis cuso 4 using cu as electrode
Exp 1: ELECTROLYSIS CuSO4 USING C AS ELECTRODE

Exp 2: ELECTROLYSIS CuSO4 USING Cu AS ELECTRODE

a 3 obsvn and inference not include the colour change of the electrolyte

a. 3 obsvn and inference (not include the colour change of the electrolyte)

inference

Observations

  • Colourless gas bubbles released at anode

Oxygen is produced

  • A brown solid is deposited at the cathode and the cathode thicker

Copper is formed at the cathode

a 3 obsvn and inference not include the colour change of the electrolyte1

a. 3 obsvn and inference (not include the colour change of the electrolyte)

inference

Observations

Copper anode dissolves to form copper (II) ions

  • The copper anode in exp II become thinner
b state one hypothesis for the experiment

b. State one hypothesis for the experiment

In the electrolysis of copper(II) sulphate solution ,the types of products formed at the electrodes depend on the types of electrodes used

slide40

Manipulated variable

The type of electrodes used

responding variable

The products formed

at anode

Concentration of

Copper(II) sulphate/ copper(II) sulphate

Constant variable

slide41

Sodium hydroxide

  • Nitric acid
  • Potassium iodide

O2

I2 but iodine is denser than water, so does not bubble

O2

slide42

In cell I, the blue colour change to light blue.In cell II. No change of colour in the solution. Explain

  • In Cell I,
  • Blue colour is due to Cu 2+ ion.
  • Cu +2 are discharged to form Cu atoms at cathode.
  • (Cu 2++ 2e  Cu)
  • So conc of Cu+2 decrease.
slide43

In cell I, the blue colour change to light blue.In cell II. No change of colour in the solution. Explain

  • In cell II,
  • Rate of ionization of copper atom to Cu+2 (CuCu2++2e) at anode is equal
  • to rate of discharge of Cu+2 to copper atoms ( Cu 2+ + 2e  Cu) at cathode.
  • So conc of Cu+2 remain constant
draw the diagram of electroplating of iron key with silver using silver nitrate solution

Draw the diagram of electroplating of iron key with silver using silver nitrate solution

Anode

cathode

Silver rod

Iron key

Silver nitrate solution

slide47

13.0

13.1

13.0

I- Lithium burns with a white flame

II- Potassium burns with a purple

flame

III- Sodium burns with a yellow flame

slide48

3 inferences from exp II

  • Potassium reacts vigorously
  • with water
  • alkaline solution is produced
  • Heat is released

Hypothesis in this experiment

  • The lower the position elements in Group I, the higher the reactivity of metals with water
slide49

e) State operational definition of of reactivity of Group I elements

  • When Group I elements are placed in water,
  • the intensity of the flame produced shows the reactivity of the elements
slide50

Arrange in ascending order of reactivity

  • Li Na K

Give reason in term of atomic size

  • Atomic size increase from lithium atom to potassium atom
  • Nuclei attraction in K atom is the most
  • K atom is the easiest to release electron to form K+ ion
slide51

Rb is placed below K in Group I element. Predict 3 observations with Rb

  • Rubidium burns very brightly
  • A lot of bubbles are produced
  • A colourless solution with pH 3.2 is produced
slide52

Manipulated variable

  • Water and methyl benzene

Responding variable

  • Effervescence / acidic properties of ethanoic acid

Constant variable

  • Ethanoic acid, magnesium
slide54

Classify the following acids into strong and weak acids

Weak acid

Ethanoic acid

Strong acid

Hydrochloric acid

Nitric acid

Sulphuric acid