form 4 answer scheme

8/3/2019 Form 4 Answer Scheme

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SEKOLAH MENENGAH KEBANGSAAN

JALAN ARANG

KUCHING

CHEMISTRY FORM FOUR

PEPERIKSAAN AKHIR TAHUN

2011

MARKING SCHEME

PAPER 1

PAPER 2

PAPER 3


2/17

Answers for Chemistry Paper 1

1 A 2 B 3 A 4 C 5 C

6 B 7 A 8 C 9 C 10 D

11 D 12 A 13 D 14 C 15 C

16 A 17 A 18 D 19 B 20 B

21 A 22 C 23 D 24 C 25 D

26 B 27 A 28 C 29 D 30 B

31 B 32 A 33 B 34 A 35 B

36 A 37 A 38 B 39 C 40 B

41 C 42 A 43 A 44 C 45 D

46 C 47 D 48 C 49 D 50 A


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3

Paper 2 Section A

1 (a) 13 1

(b) 20// 21 1(c) (i) Atoms of the same element which have same proton

number but different number of neutron

1

(ii) B & E 1

(d) (i) correct number of neutron(ii) correct number of proton(iii) correct number of shell and electron

1

11 3

(e) (i) D 1

(ii) A 1

(f) 2.8 1

10

2 (a) The metal oxide burns / glows // droplets of a colourless

liquid formed

1

(b) Anhydrous calcium chlorideto dry the hydrogen gas

11 2

(c)

M O

Mass (g) 92.02 42.34= 49.68

95.86 92.02= 3.84

No. of mol 49.68/ 207 =

0.24

3.84/ 16 =

0.24Simplest

mol ratio

1 1

Empirical formula is MO

1

1

1

1 4

(d) (i) correct reactant(ii) correct product

MO + H2 M + H2O

1

1 2

9

3 (a) (i) Group 1, Period 4 1+1 2

(ii) G 1

(b) (i) D2L 1

(ii) Soluble in water // High melting/ boiling point // Can

conduct electricity in molten or aqueous state

1

(c) (i) E 1

(ii) Nuclei attraction towards valence electrons is weaker in E 1


4/17

4

Thus, it is easier for atom of E to release an electron to

form a positively charged ion 1 2

(d) (i) L / M 1

(ii) Covalent bond 1

10

4 (a) XY3 1

(b) (i) Covalent bond 1

(ii) 2.5 1

(iii) X: Group: 15 , Period : 2

Y: Group : 17 , Period : 2

1

1 2

(c) Low melting and boiling point//cannot conduct

electricity// dissolve in organic solvent

1

(e) (i) correct reactant(ii) correct product(iii) balance equation

X2 + 3Y2 2XY3

1

1

1 3

9

5 (a) P : - , Q : + 1

(b) o allow the ion to flow through 1

(c) - from chemical energy to electrical energy 1

(d) Iron / P is more electropositive than copper / Q // iron is

placed higher than copper in the electrochemical series 1

(e) (i) Intensity of the blue solution decrease 1

(ii) Cu2+

+ 2 e Cu 1

(f) (i) copper electrode / R becomes thicker // a brown solid

deposited

1

(ii) R : - , S : + 1(g) (i) voltage in Figure 5.2 is higher than in Figure 5.1I / more

than 1.2 V

1

(ii) he distance between zinc and copper in the electrochemical

series is further than that between iron and copper

1

10

6 (a) Strong acid is an acid which ionizes completely in water

to produce high concentration of hydrogen ions.

1

1 2

(b) Neutralisation 1

(c) (iv) correct reactant(v) correct product(vi) balance equation

2NaOH + H2SO4 Na2SO4 + 2 H2O

1

1

1 3

(d) Pink to colourless 1

(e) From the equation in (c).

1 mole of H2SO4 reacts with 2 moles of NaOH


5/17

5

1.0x 20.00 = 1MNaOH x 25.00 2

MNaOH = 1.6 moldm-3

1

1 2

(f) 2.0 moldm-3 1

(g) Twice / 50.00 cm3

1

(h) Ammonium sulphate 1

12

Section B

7 (a) (i) Bond which formed when two or more atom share thevalence electron

to achieved the stable electron arrangement

1

1 2

(ii) Ionic bond:

1. Between atom B and C

2. Atom B has electron arrangement 2.8.1

3 .Atom B will donate 1 valence electron4 .to achieve the stable electron arrangement

5 .and become positively charged ion// B B+ + e

6. Atom C has 6 valence electron7. accept 2 electron and become negatively charge ion//

C + 2e

C2-

8. 2 atom B will donate1 electron each to 1 atom C

9 The force of attraction between ions are very strong

Covalent bond:

10. Between atom C and D

11. To achieve the stable electron arrangement12. One atom D will share 4 electron with 2 atom C

13. Force of attraction between molecules are weaker

1

1

11

1

1

11

1

1

11

1 13


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6

(iii)Type of

Compound

Ionic compound Covalent

compound

Melting point &

Boiling point

Higher Lower

Electric

Conductivity

Can conduct

electricity in

molten state oraqueous

solution

Cannot conduct

electricity

Solubility

Dissolve in

water but

cannot inorganic solvent

Dissolve in

organic solvent

but cannot inwater

1

1

1

3

(b) Atom L has 2 valence electron,Donate 2 electron to achive the stable electronarrangement

11 2

20

8 (a) Alkali A sodium hydroxide/ barium hydroxide /

potassium hydroxidestrong alkali

ionises completely in water to produce high concentration

of OH-

Alkali B ammonia solutionWeak alkali

Ionizes partially in water to produce low concentration of

OH-

11

1

11

1 6

(b) (i) X : methylbenzene/ tetrachloromethane/ any organic

solventsY : water

1

1 2

(ii) Hydrogen chloride ionizes completely in waterto form H+, so solution X shows acidic properties .

Without water, hydrogen chloride exists as molecules

There are no H

+

present, so solution Y does not showacidic properties

11

1

1 4


7/17

7

(c) Calculation2.0x Volume acid = 1.0 x 100

Volume acid = 1.0 x 100 //

2.0= 50 cm3

1. Use a pipette to draw up 50 cm3 2.0 moldm-3sulphuric acid .

2. Transfer the acid to a 100 cm3 volumetric flask.3. Add distilled water to bring the level of solution

until the calibration mark.

4. Stopper the flask and shake well.

1

1

1

1

1

1 6

(d) Add powdered lime/ lime stone / ashes of burnt wood

Reason weak alkali, can neutralize acidity in the soil

1

1 220

Section C

9 (a) Salt is an ionic compound formed when the hydrogen ionin an acid is replaced by a metal ion or an ammonium ion 1

(b) Material

2 mol dm-3

nitric acid, copper (II) oxide powder

Apparatus

250 cm3

beaker, glass rod, filter funnel, retort stand andclamp, Bunsen burner, 250 cm3 conical flask, filter paper,

evaporating dish, 50 cm3 measuring cylinder, spatula.

Procedure

1.

Pour 50 cm

3

of 2 mol dm

-3

nitric acid into a beaker.2. Warm the acid.3. Add copper(II) oxide powder bit by bit into the

acid.

4. Stir the mixture .

1

1

11

1

1


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8

5. Add copper(IIl) oxide until some of it no longerdissolve.

6. Filter the mixture.7. Heat the filtrate until it become saturated.8. Let it cool9. Filter out the crystals.10.Dry the crystal using the dry filter paper.

Chemical equation:

2 HNO3 + CuO Cu(NO3)2 + H2 O

1

1

1

1

1

1

113

(c) (i) Acid + alkali salt + waterExample:

HCl + NaOHNaCl + H2O

(ii) Acid + metal salt + hydrogenExample :2HNO3 + MgMg(NO3)2 + H2

(iii) Acid + base salt + waterExample:H2SO4 + CuO CuSO4 + H2O

(iv) Acid + metal carbonate salt + water + carbondioxide.Example:

2HCl + CaCO3 CaCl2 + H2O + CO2

1

1

1

1

1

1

1

1

Max

6

20


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9

10 (a) Solid sodium chloride consists of ions which are held in

fixed positions by strong ionic bonds and are not freely

moving.In aqueous sodium chloride, the ionic bonds are broken

and the ions move freely.

1

1 2

Materials : 0.1 mol dm-3

silver nitate solution, woodensplinter, sandpaper

Apparatus: Batteries, carbon electrodes, silver

lectrodes,

electrolytic cell, connecting wires with crocodile clips,ammeter, test tube and switch.

[ or labelled diagram of set-up of apparatus]

Procedure :

1. An electrolytic cell is half-filled with 0.1 mol dm-3silver nitrate solution.

. The electrodes are connected to batteries and anammeter with connecting wires.

. A test tube filled with silver nitrate solution isinverted over the anode.

. The switch is turned on and electric current is allowedto flow for 15 minutes.

.

Observations at anode and cathode are recorded.. Steps 1- 6 are repeated using silver electrodes in place

of carbon electrodes..Observations:

Observation

Electrode Anode Cathode

Carbon

Bubbles of

colourless gasreleased, relights a

glowing woodensplinter.

A shiny, grey

solid deposited.

Silver

Silver electrode

becomes thinner.

A shiny, grey

solid deposited //cathode becomes

thicker

1

1

1

1

1

1

1

1

1+1

1+1


10/17

ilver nitrate solution consists of Ag +, NO3- , H + ,

H-

ions .

When carbon is made the anode , OH-ions are selectively

ischarged because they are lower than NO3-

ions in the electrochemical series to produce oxygen gas

/

4 OH- O2 + 2 H2O + 4 e

At the cathode, Ag + ions are lower than H + ions in the

lectrochemical series and are selectively discharged toorm silver metal //

Ag + + e Ag

When silver is made the anode, silver atoms ionise to

form Ag

+

ions. The silver anode dissolves //Ag Ag + + e

At the cathode, Ag + ions are lower than H + ions in the

lectrochemical series and are selectively discharged to

orm silver metal //Ag + + e Ag

1

1

1

1

1

17

(ii) Type of electrode// Concentration of electrolyte//

position of ion in Electrochemical Series.

1

20

END OF MARKING SCHEME


11/17

SULIT 4541/32

MARKING SCHEME

CHEMISTRY 3 , 4541/3

Question Rubric Score

1(a)

Able to state all the voltmeter readings accurately with correct unit and

one decimal point.

Sample answer:

Mg and W : 2.0 V

Mg and X : 0.6 V

Mg and Y : 1.4 V

Mg and Z : 2.5 V

3

Able to state all the voltmeter readings accurately without unit.

Sample answer:

Mg and W : 2

Mg and X : 0.60

Mg and Y : 1.4

Mg and Z : 2.5

2

Able to state at least two readings correctly without unit 1

No response or wrong response 0


1(b )

Able to construct a table to record the voltmeter reading for each pair of

metals that contain:

1. Correct titles

2. Readings

Sample answer:

Pairs of metals Voltage / V

Mg and W 2.0

Mg and X 0.6

Mg and Y 1.4

Mg and Z 2.5

3

Able to construct a less accurate table that contains:1. Titles

2. Readings

2

Able to construct a table with at least one title / reading 1



12/17

SULIT 4541/33


1(c )

Able to give the hypothesis accurately

Sample answer:

The further the distance between two metals in the electrochemical series,

the higher the potential difference / voltage

3

Able to give the hypothesis almost accurately

Sample answer:

The further the distance between two metals, the higher potential

difference/voltage // vice versa

2

Able to state an idea of hypothesis

Sample answer:

Different metals affects the potential difference

1



1(d )

Able to state all the three variables correctly

Sample answer:

Manipulated variable: Pair of metal

Responding variable: Voltmeter reading/voltage

Constant variable: magnesium/negative electrode, sodium

Chloride solution//electrolyte

r: volume of sodium chloride/electrolyte

3

Able to state any two variables correctly 2

Able to state any one variable correctly 1



1(e)

Able to arrange in ascending order of all the metals

Sample answer:

Z, W, Y, X, Mg

3

Able to arrange any four metals in correct ascen ding order 2

Able to arrange any three metals in correct ascending order 1No response or wrong response 0


1(f)

Able to predict the value of voltage accurately with unit.

Answer:

1.9 V

3

Able to predict the value of voltage accurately without unit.

Answer:

1.9

2

Able to give an idea the value of voltage.

1.4 < V < 2.5

1



13/17

SULIT 4541/34


2(a)

Able to state the observation and corresponding infences correctly

Sample answer:

Test tube Observation Inference

A - No reaction

B Bubbles of gas

produced

Hydrogen gas releases

3

Able to state any two answer correctly 2

Able to state any one answer correctly 1

No response given / wrong response 0


2(b)

Able to give the meaning of acid correctlySample answer:

Substance that produced hydrogen gas when reacts with zinc.

3

Able to give the meaning of acid.

Sample answer:

Substance that ionize/dissolve in water to produce hydrogen ion //

substance that produce bubbles when reacts with zinc.

2

Able to give an idea of acid

Sample answer:

Substance that change blue litmus paper to red // substance that has pH

value lower than 7.

1



2(c)

Able to explain the role of water correctly

Sample answer:

Water can ionise/dissociate acid to form hydrogen ion.

3

Able to explain the role of water less accurately

Sample answer:

Water can ionise/dissociate acid // water can produce hydrogen ion.

2

Able to give an idea of the role of water.

Sample answer:To show the acidity of acid.

1



14/17

SULIT 4541/35


2(d)

Able to write the name of any two products correctly

Sample answer:

1. Zinc ethanoate

2. Carbon dioxide3. water

3

Able to write the name of any one product correctly or any two products

less accurately

Sample answer:

1. zinc ethanoate // carbon dioxide // water

2. CO2 and H2O//(CH3COO)2Zn and CO2//(CH3COO)2Zn and H2O

2

Able to state an idea of the product.

Sample answer:

(CH3COO)2Zn // CO2 // H2O

1



2(e)

Able to classify all the acids correctly

Sample answer:

Strong acid Weak acid

Hydrochloric acid. HCl

Nitric acid, HNO3Sulphuric acid, H2SO4

Phosphoric acid, H3PO4Carbonic acid, H2CO3Methanoic acid, HCOOH

3

Able to classify any four acids correctly 2

Able to classify any two acids correctly or give opposite heading

Sample answer:

Weak acid Strong acid

Hydrochloric acid. HCl

Nitric acid, HNO3Sulphuric acid, H2SO4

Phosphoric acid, H3PO4Carbonic acid, H2CO3Methanoic acid, HCOOH

1



15/17


3(a)

Able to give the problem statement of the experiment correctly

Sample answer :

Does an acid/glacial ethanoic acid need water to show its acidicproperties? //

Is water needed for an acid/ glacial ethanoic acid to show its acidic

properties?

3

Able to give the problem statement of the experiment incorrectly

Sample answer :

To investigate/study the role of water in showing the properties of

an acid.

2

Able to state an idea of problem statement of the experiment

Sample answer :

Water is needed to show the properties of acid. 1No response or wrong response 0


3(b)

Able to state All variables correctly

Sample answer :

Manipulated variable : Presence of water

Responding variable : Acidic properties // Gas produced

Constant variable : Acid // glacial ethanoic acid // magnesiumr : Volume of acid

3

Able to state any two variables correctly 2

Able to state any one variables correctly 1



16/17

SULIT 16 4541


3(d)

Able to give the list of the apparatus and materials correctly

and completely

Sample answer :

Apparatus : dry test tube

Material : Glacial ethanoic acid, water, magnesium ribbon,

wooden splinter

3

Able to give the list of the apparatus and materials correctly

but not completely

Sample answer :

Dry test tube

Glacial ethanoic acid, water, magnesium ribbon

2

Able to give an idea about the list of the apparatus and

substances correctly

Sample answer :

Test tube and any one substance

1



3(c)

Able to give the hypothesis correctly

Sample answer :

Water is needed for an acid to show its acidic properties //

Presence of water is essential for an acid to show its acidicproperties.

3

Able to give the hypothesis almost correct

Sample answer :

Ethanoic acid/An acid shows its acidic properties when water is

present //The presence of water influence the acidic properties

of acid

2

Able to state an idea of the hypothesis

Sample answer :

The water affect the properties of acid

1



17/17

SULIT 17 4541


3(e)

Able to state all procedures correctly

Sample answer :

1. Glacial ethanoic acid is poured into two different dry testtube labeled A and B.

2. Distilled water is added into glacial ethanoic acid in testtube B.

3. A piece of magnesium ribbon is put into test tube A and B.4. A lighted wooden splinter is placed at the mouth of both test

tubes.

5. The observation is recorded.

3

Able to list down steps 1, 2 and 3 2

Able to list down steps 1 and 3 or 2 and 3 1



3(f)

Able to exhibit the tabulation of data that includes the following

two information correctly

1. Heading for the manipulated variable2. Heading for the responding variable

Sample answer :

(Test tube) //

(Condition of acid)

Observation

Test tube A //Glacial

ethanoic acid

Test tube B

//Ethanoic acidsolution /in water

2

Able to exhibit the tabulation of data less accurately

Tabulation of data has the following elements :

1. Heading for the manipulated variable2.

Heading for the responding variable3. One condition of acid listed

Sample answer :

Acid/test tube Effect//Result

Glacial ethanoic acid

1


END OF MARKING SCHEME

form 4 answer scheme

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