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)
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

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)

2. State Op Def for 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.

3. State Op Def for 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.

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

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

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

3. 5. Voltaic cell
When two different metals are dipped into an electrolyte
The needle of the voltmeter deflects//Voltmeter shows a reading

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

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

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

Hypothesis: ( early conclusion to aim of exp)
Statement that relates the MV followed by responding variable with direction.
Example:
1. The higher temperature of the reactant the higher the rate of reaction – 3 marks
2. Hexene decolourised brown bromine water but hexane does not

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

Exp
Does size of calcium carbonate affect rate of reaction?
MV RV Hypothesis
(MV→RV)
Size of calcium carbonate
Rate of reactio n
When size of calcium carbonate is smaller, the rate of reaction increases

Exp MV RV Hypothesis (MV→RV)
To differentia te between hexene and hexane
Hexen e and hexan e
Decolouri sed brown bromine water
When hexene is added to bromine water, brown colour decolorized, but when hexane is added to bromine water, brown bromine not changed

Exp MV RV Hypothesis (MV→RV)
Heat of combusti on of different types of alcohols
Types of alcohol s
Heat of combusti on
When no of carbon atoms per molecule alcohol increases, the heat of combustion increase

Exp MV RV Hypothesis (MV→RV)
Coagul ation of latex
Acid and ammonia solution
Coagulat ion of latex
When acid is added to latex, coagulation of latex occurs, but when ammonia solution is added to latex, NO coagulation occur

How is the reading of apparatus taken? to 1 decimal point or 2 decimal point?
20.40
24.0
1.6
1.30

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

Set
I
II
Latex + ethanoic acid
Latex + ammonia
III
Latex only
Apparatus set-up
Latex coagulate
Latex + not coagulate
Latex coagulate

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

(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

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

(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

When acid is added to latex, it becomes solid

Ethanoic acid / Acid/(Ammonia solution) / Alkali
Coagulate //Time taken for coagulation
Vol of latex / acid / (ammonia solution)
/ alkali // latex /temp

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

(ii) Explain the answer in l(g) (i).
bacteria in air reacts with latex to produce lactic acid ( H + )
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

(h) Explain why latex can coagulate without acid in Set III.
Bacteria in air reacts with latex to produce lactic acid / H +
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

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

(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.

Nitric acid
Methanoic acid
Potassium hydroxide
Sodium hydroxide

SPM-P3 2009

Exp 1: ELECTROLYSIS CuSO
4
Exp 2: ELECTROLYSIS CuSO
4
USING C AS ELECTRODE
USING Cu AS ELECTRODE

a. 3 obsvn and inference (not include the colour change of the electrolyte)
Observations inference
• 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 electrolyte)
Observations inference
• The copper anode in exp II become thinner
Copper anode dissolves to form copper (II) ions

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

Manipulated variable The type of electrodes used responding variable The products formed at anode
Constant variable Concentration of
Copper(II) sulphate/ copper(II) sulphate

Solution that produced gas at the anode when electrolysed
• Sodium hydroxide
O
2
• Nitric acid O
2
Solution that does not produced gas at the anode when electrolysed
• Potassium iodide
I
2 but iodine is denser than water, so does not bubble

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.

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  Cu 2+ +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
Iron key cathode
Anode
Silver rod
Silver nitrate solution

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

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

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

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

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

Manipulated variable
• Water and methyl benzene
Responding variable
• Effervescence / acidic properties of ethanoic acid
Constant variable
• Ethanoic acid, magnesium

Sketch a graph of the volume of hydrogen gas againsts time

Classify the following acids into strong and weak acids
Strong acid
Hydrochloric acid
Nitric acid
Sulphuric acid
Weak acid
Ethanoic acid