MRSM PENGKALAN CHEPACHEMISTRY 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 MV RV Hypothesis (MV→RV)

Does size of calcium carbonate affect rate of reaction?

Size of calcium carbonate

Rate of reaction

When size of calcium carbonate is smaller, the rate of reaction increases

Exp MV RV Hypothesis (MV→RV)

To differentiate between hexene and hexane

Hexene and hexane

Decolourised 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 combustion of different types of alcohols

Types of alcohols

Heat of combustion

When no of carbon atoms per molecule alcohol increases, the heat of combustion increase

Exp MV RV Hypothesis (MV→RV)

Coagulation of latex

Acid and ammonia solution

Coagulation 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

STRUCTURE PAPER 3

2008

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.

Set Apparatus set-up

I

II

III

Latex + ethanoic

acid

Latex coagulate

Latex + ammonia

Latex + not

coagulate

Latex only

Latex coagulate

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

Acid coagulate latex while alkali does not coagulate the latex

(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.

Set Time taken

I 5 minutes

III 6 hours

(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 / LiquidSet III : Latex coagulates / A solid lump is formed

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

When acid is added to latex,

it becomes solid

(f) Manipulated variable:

Responding variable :

Constant variable :

Ethanoic acid / Acid/(Ammonia solution) / Alkali

Coagulate //Time taken for coagulation

Vol of latex / acid / (ammonia solution) / alkali // latex /temp

(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

(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.

Can coagulate latex

Cannot coagulate latex

Nitric acidMethanoic acid

Potassium hydroxideSodium hydroxide

SPM-P3 2009

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)

• Colourless gas bubbles released at anode

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

Oxygen is produced

Copper is formed at the cathode

Observations inference

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

• The copper anode in exp II become thinner

Copper anode dissolves to form copper (II) ions

Observations inference

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

The type of electrodes used

The products formed at anode

Concentration of Copper(II) sulphate/ copper(II) sulphate

Manipulated variable

responding variable

Constant variable

Solution that produced gas at the anode when electrolysed

Solution that does not produced gas at the anode when electrolysed

• Sodium hydroxide

• Nitric acid

• Potassium iodide O2

O2

I2 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. ExplainIn 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

(CuCu 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

Silver nitrate solution

Iron key

Silver rod

cathode Anode

SPM PAPER 3 STRUCTURES

2010

13.013.113.0

I- Lithium burns with a white flame

II- Potassium burns with a purple flame

III- Sodium burns with a yellow flame

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

3 inferences from exp II

Hypothesis in this experiment• The lower the position elements in

Group I, the higher the reactivity of metals with water

• When Group I elements are placed in water,

• the intensity of the flame produced shows the reactivity of the elements

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

• Li Na K

• 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

Arrange in ascending order of reactivity

Give reason in term of atomic size

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

produced

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

Manipulated variable

Responding variable

Constant variable

• Water and methyl benzene

• Effervescence / acidic properties of ethanoic acid

• Ethanoic acid, magnesium

Sketch a graph of the volume of hydrogen gas againsts time

Strong acidHydrochloric acidNitric acid Sulphuric acid

Weak acid Ethanoic acid

Classify the following acids into strong and weak acids