SET 1 CCA Answer Scheme

7/28/2019 SET 1 CCA Answer Scheme

1/12

Chemistry Confirm A-SET 1

MARKING SCHEME FOR STRUCTURED QUESTIONS:

No MARKING CRITERIA MARK

SUB TOTAL1(a) (i) The temperature at which a solid changes into a liquid 1

(ii) Liquid 1(b) P : MoleculeQ : Ion

11

(c)

1

(d) R 1(e) The force of attraction between the Q particles/ ions is

stronger than the P particles/ molecules. More heat energy is needed to overcome the forces of

attraction between Q particles.

1

1

(f) In solid state, the particles/ ions of Q cannot move

freely.

In molten state, the particles/ ions of Q are mobile/ can

move freely.

1

1

11

2(a) To ensure that the naphthalene is heated evenly/ uniform 1

(b) Molten napthalene is stirred throughout the cooling process 1(c) (i)

2

1

Temperature/ o C

Time/ S

78


2/12


2

3(a) The mass of one atom of element when compared with

121 of the mass of a Carbon-12 atom

1

(b) 16 1

(c) 2

(d) 2

2

Temperature/ o C

Time/ S

78

Oxygen molecule


3/12


(e)

Empirical formula = Al2O3

2

(f)No. of moles =

1027.1 = 0.0167 1

(g) Number of Al3+ ion = 2 X 0.0167 X 6.02 X 1023 //2.1 X 1022 ions 1

15

4(a) The chemical formulae which shows the simplest wholenumber ratio of atoms of of each element present in a

compound

1

(b) (i) Mass of magnesium = 26.4 24.0 // 2.4 gMass of oxygen = 28.0 26.4 // 1.6 g 1

3

Element Aluminium Oxygen

Mass(g) 0.91 1.70-0.91 = 0.79

No. ofmoles 27

91.0 //

0.0337

1679.0 // 0.0494

Simplestratio ofmoles

0337.00337.0 //

1

0333.00494.0 //

1.5

2 3


4/12


(ii)

2

(iii) MgO 1

(iv) 2Mg + O2 2MgO 1(c) To remove the oxide layer on its surface 1

(d) To allow oxygen to enter the crucuble 1(e) Zinc / Aluminium / Calcium 1

9

5(a) Black1

(b)

Metal oxide

Dry hidrogen gas

Burning of excess

hydrogen gas

Heat

# functional diagram

# labell

11

(c) Make sure all the connections are tightly fixed 1

(d) (i) Mass of copper = 38.76 36.20 // 2.56 gMass of oxygen = 39.40 38.76 // 0.64 g 1

(ii)Moles of magnesium : Moles of oxygen

64

56.2 :16

64.0

0.04 : 0.041 : 1

2

(iii) CuO 1(e) CuO + H2 Cu + H2O 1

(f) No.Magnesium is more reactive than hydrogen

11

11

6(a) (i) The number of protons in the nucleus of an atom 1

(ii) The total number of protons and neutrons in the nucleus ofan atom 1

4

No. of moles ofMagnesium

No. of moles of oxygen

244.2

166.1

0.1 0.11 1


5/12


(b) (i) P and Q 1

(ii) P and Q have the same proton number and differencenucleon number 1

(c) Electrons = 7Protons = 7

11

(d) P : 2.4

R : 2.5

1

1(e) 5 1

9

7(a) (i) A // B 1

(ii) Alkaline 1

(iii) 2A + 2H2O 2AOH + H2// 2B + 2H2O 2BOH + H2

2

(b) (i) C 1

(ii) formed coloured ions or compounds //have more than one oxidation numbers in its compound //formed complex ions //act as a catalyst

1

(c) 8 1

(d) To fill advertising light bulbs 1(e)

1

(f) Molecules

(g) The forces of attraction between the molecules of H is

stronger than the molecules of E

The molecules of H are packed closely together

1

1

11

5

M


6/12


MARKING SCHEME FOR ESSAY QUESTIONS:


SUB TOTAL

1 (a) Group 18 / 18

Argon atom has attained octet electron arrangement//

Argon atom has 8 valence electrons//Argon atoms outermost shell is completely filled withelectrons.

The electron arrangement is stable . Does not need to gain, lose or share electrons.

1

1

11

4

(b) Perfume is made up of tiny particles

particles of the perfume diffuse into air particles.

the particles move randomly.

into the students nose //student can sense the smell of the

perfume.

1

111

4

(c)

1

1

6


7/12


13

(d)(i) The iron wool burns vigorously with a bright flame.

A brown solid is formed.

11 2

(ii) Number of moles of iron =

56

8.2 // 0.05

2 moles of Fe produce 2 moles of FeCl3 //

0.05 mole of Fe produce 0.05 mole of FeCl3 Relative formula mass = 56 +3 (35.5) // 162.5

Mass of FeCl3 = 0.05 162.5 // 8.125 g

1

1

1

1 4

17

2(a) Freezing

The heat energy released is equal to the heat energy lost to the

surrounding.

11+1 3

(b)(i) At 80oC : Solid

At 280oC : Gas

11 2

7

P Q

Arrangement ofparticles

The particles arepacked closelytogether but not inorderly

arrangement

The particles arevery far apart fromeach other and inrandom

arrangement

Force of attractionbetween particles

Strong Weak

Energy content High Higher


8/12


Temperature 80oC (Solid) 280oC (Gas)Arrangement ofparticles

Particles areorderly andcloselypackedtogether.

Particles are farapart.

Movement ofparticles

Vibrating androtating about intheir fixed positions.

Particles moverandomly andrapidly in alldirections.

The forces ofattraction

Strong Weak

Kinetic energy Low High

Note: 1 mark for each correct comparison.

1

1

1

1 4

(ii) Able to describe the procedure correctly.

Example:1. A boiling tube is filled with powder of compound M to a

depth of (3-4) cm.2. A thermometer is placed into powder of compound M in the

boiling tube.3. A 500 ml beaker is filled with coconut oil/palm oil until it is

full.4. The boiling tube is immersed into the coconut oil.5. The coconut oil is heated and the stopwatch is started.6. Stir the compound M.7. The temperature is recorded at 30-second intervals until its

melt completely.

Result:

Time(s) 0 30

60

90

120

150

180

210

240

Temperature(oC)

[The graph of temperature against time for the heating of compoundM is plotted.]

1

1

1

1111

1

1+1

7Max 6

8

Temperature (OC)

Time (s)

ToC


9/12


(Must indicate T in the graph)

Conclusion:

The melting point of compound M is T oC.

1 4

20


SUB TOTAL

3(a) the reaction between L and water is more reactive.

the atomic size of L is bigger.

the distance between nucleus of atom L and valence electron

is more further away.

the valence electron electron of atom L is easier to release.

111

1

4

(b)(i) Ionic bond

atom L release one valence electron to produce ion L +

Atom M receive one electron to form ion M-

To achieve stable electron arrangement.

Ions L+ and ions Y- are attracted to each other with strong

Electrostatic force

Form ionic compound LM

11111

1 6

(ii) Covalent bond

valence electrons of atom N and M are 4 and 7 respectively

atom N contributes 4 electrons and atom M contribute one

electron

to achieve stable electron arrangement

one atom N share electrons with 4 atom M // each of atom M

share a pair of electron with atom N

to form a covalent compound, NM4

11

11

11

6

(c) High melting point / boiling point

soluble in water

can conduct electricity in molten/ aqueous state

#any 2 correct answers

11

1

2

(d) Can form coloured ions / compound

have more than one oxidation number

can act as a catalyst

#any 2 correct answers

111

2

9


10/12


20

4(a) W : 2.4Z : 2.8.7

11 2

(b) X is in group 16 and period 2

Atom X has 6 valence electron

Have 2 shell occupied with electrons

111 3

(c) The electron arrangement of atom Y and atom Z are 2.8.2

and 2.8.7

Atom Y release 2 electrons to form ion Y2+

Atom Y receive one electron to form ion Z-

to achieve a stable electron arrangement

ions Y2+ and ion Z are attracted to each other with strong

electrostatic force

to form an ionic compound YZ2

the electron arrangement of atom X and atom W are 2.6 and

2.4

atom W contributes 4 electrons and atom X contribute 2electrons

to achieve a stable electron arrangement

one atom W share electrons with 2 atoms X // each of atom X

share two pairs of electron with atom W

to form a covalent compound, WX2

1

1111

11

1

11

1

1

4

7

(d) Boiling point of ionic compound is higher

the force of attraction between ions in the ionic compound is

stronger // the force of attraction between the molecules in thecovalent compound is weaker

more heat energy is needed to overcome the forces ofattraction between the ions

ionic compound can conduct electricity in molten or aqueous

state while covalent compound cannot conduct electricity

in molten / aqueous state the ions of ionic compound are

mobile / move freely

covalent compound consist of molecules

1

1

1

1

1

1

6

23

MARKING SCHEME FOR PAPER 3


SUB TOTAL1(a) At 270 s 83.0

At 300s 87.0 3(b) Criteria for graph

(i) Labelled axes with correct units(ii) Transfer all the points correctly

3

10


11/12


(iii) Correct shape of the curve and smooth

(c) 80 o C (must be shown in the graph)3

(d) Heat absorbed is used to overcome the force of attractionbetween the molecules of naphthalene 3

(e) Less than 80 o C3

f(i) Manipulated : Napthalene and acethamideResponding : Melting pointFixed : Height of the naphthalene and acethamide

3

(ii) Napthalene and acethamide have different melting points 3

21

3 (a) Problem statement

Score

3

[ Able to state the problem statement clearly and accurately]

Suggested answer

Does the reactivity of Group 1 elements increase down the group when reactwith water?

(b) Stating all variables

Score

3

[Able to state all the corresponding variables accurately]

Suggested answer

Manipulated variable : Type of Group 1 metals

Responding variable : Movement of the Group I metal

Fixed variables : Water, size of metals

(c) List of materials and apparatus

Score

3[Able to list all materials and apparatus correctly]

Suggested answer

Materials

A small piece of lithium, sodium, potassium and water

11


12/12


Apparatus

Trough// basin //suitable container, forceps, Knife, filter paper

(d) Experimental procedure

Score

3

[Able to state all experimental steps correctly]

Suggested answer

1. Cut a small piece of lithium using a knife and forceps.

2. Dry the oil on the surface of the lithium with filter paper.

3. Place the lithium slowly onto the water surface

4. Observe the reactivity of the reaction

5. Repeat steps 1 to 4 using sodium and potassium to replace lithium

(e) Tabulation of data

Score

3

[Able to construct a table correctly containing the following elements]

- Columns and rows

- Observation for each metal

Suggested answer

Metals Observations

Lithium

Sodium

Potassium

12

Documents

SET 1 CCA Answer Scheme