Download - SET 1 CCA Answer Scheme
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7/28/2019 SET 1 CCA Answer Scheme
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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
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(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
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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
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Chemistry Confirm A-SET 1
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
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Oxygen molecule
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Chemistry Confirm A-SET 1
(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
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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
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Chemistry Confirm A-SET 1
(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
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5(a) Black1
(b)
Metal oxide
Dry hidrogen gas
Burning of excess
hydrogen gas
Heat
# functional diagram
# labell
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(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
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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
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Chemistry Confirm A-SET 1
(b) (i) P and Q 1
(ii) P and Q have the same proton number and differencenucleon number 1
(c) Electrons = 7Protons = 7
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(d) P : 2.4
R : 2.5
1
1(e) 5 1
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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
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5
M
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Chemistry Confirm A-SET 1
MARKING SCHEME FOR ESSAY QUESTIONS:
No MARKING CRITERIA MARK
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
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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
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(c)
1
1
6
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Chemistry Confirm A-SET 1
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(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
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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
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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
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Chemistry Confirm A-SET 1
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
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(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
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Chemistry Confirm A-SET 1
(Must indicate T in the graph)
Conclusion:
The melting point of compound M is T oC.
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No MARKING CRITERIA MARK
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.
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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
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(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
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11
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(c) High melting point / boiling point
soluble in water
can conduct electricity in molten/ aqueous state
#any 2 correct answers
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1
2
(d) Can form coloured ions / compound
have more than one oxidation number
can act as a catalyst
#any 2 correct answers
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2
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Chemistry Confirm A-SET 1
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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
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(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
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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
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MARKING SCHEME FOR PAPER 3
No MARKING CRITERIA MARK
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
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Chemistry Confirm A-SET 1
(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
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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
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Chemistry Confirm A-SET 1
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
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