Kimia Set 1 Perfect Score[1]

Set 1

Chemistry Perfect Score Module 2007

PAPER 2 – STRUCTURE SECTION A 1

In an experiment to determine the empirical formula of an oxide of copper , the combustion tube with the porcelain dish are weighed. Oxide of copper is added into the porcelain dish and the tube is weighed again. The oxide of copper is heated strongly. After the set of apparatus cools down to room temperature the combustion tube with its content is weighed again. The following data is obtained.

Mass of combustion tube + porcelain dish Mass of combustion tube + porcelain dish + oxide of copper Mass of combustion tube +porcelain dish + copper

= = =

19.60 g 25.68 g 24.46 g

(a)

What is meant by empirical formula?

(b)

………………………………………………………………………………………………………………. [ 1 mark ] Draw a labelled diagram of the set-up of the apparatus for the experiment.

[ 2 marks ] (c)

Calculate the empirical formula of the oxide of copper. Given that the relative atomic mass of O=16 , Cu=64

[ 3 marks ]

(d)

Write the chemical equation for the reaction in the experiment. ……………………………………………………………………………………..................................... [ 1 mark ]

(e)

Before oxide of copper is heated, hydrogen gas is allowed to pass through the apparatus until all the air in the combustion tube is completely removed. Describe the steps that should be taken to ensure that all air in the combustion tube has been removed. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. [3 marks ]

Set 1

1

Set 1

Chemistry Perfect Score Module 2007 (f)

Can the empirical formula of aluminium oxide be determined using the same method as above? Explain your answer. ……………………………………………………………………………………..................................... ……………………………………………………………………………………..................................... [ 2 marks ]

2

Table 2 shows proton number and nucleon number for atom W, X and Y. Atom

Proton number

Nucleon number

W

11

23

X

17

35

Y

17

37

TABLE 2 (a)

(b)

What is meant by : (i)

proton number ?

(ii)

....................................................................………………………………………................. [1 mark] nucleon number ?

(i)

................................. ...................................………………………………………................ [1 mark] What is meant by isotope?

(ii)

........................................................................................................................................... [1 mark] State the atoms which are isotope. ........................................................................................................................................... [1 mark]

(c)

State the number of protons, electrons and neutrons in atom W The number of protons: ................................................................................................................. The number of electrons: .............................................................................................................. The number of neutrons: ............................................................................................................... [3 marks]

(d)

Write the electron arrangement of atom X ................................................................………………………………………………...... [1 mark]

(e)

Draw the electron arrangement for atom Y

[1 mark]

Set 1

2

Set 1

Chemistry Perfect Score Module 2007 (f)

(i)

What is meant by valence electron?

(ii)

.....................................................................................………………………….................. [1 mark] What is the number of valence electron of atom W ? ........................................................................................................................................... [1 mark]

(g)

Write the symbol of atom X in the form of

A z

X.

........................................................................................................................................................ [1 mark]

3

Diagram 3 shows part of the Periodic Table of Elements.V,W,X,Y and Z do not represent the actual symbol of the elements. 1

18 2

13

V

14 X

15

16

17 Z Y

W DIAGRAM 3

(a)

Write the electron arrangement of Y ion.

(b)

……………………………………………………………………………………..................................... [ 1 mark ] (i) Which of the element is not chemically reactive.

. (ii)

(c)

........................................................................................................................................... [ 1 mark ] Explain your answer in (b)(i).

........................................................................................................................................... [ 1 mark ] V and W are located in the same group in the Periodic Table of Elements. (i)

Which of the element is more reactive?

(ii)

..............................................................................................................…......................... [ 1 mark ] Explain your answer in (c)(i).

…………………………………………………………………………...................................... …………………………………………………………………………...................................... …………………………………………………………………………...................................... [ 3 marks]

Set 1

3

Set 1

Chemistry Perfect Score Module 2007 (d)

(e)

V reacts with Y to form a compound. State one physical property of the compound formed. …………………………………………………………………………………........................................ [ 1 mark ] X reacts with Y to form a compound. Draw the electron arrangement for the compound formed.

[ 2 marks] 4

Table 4 shows the electron arrangement of atoms of elements E, F, G, H, J, and L. Element

(a)

(b)

E F

Electron arrangement of atom 1 2.4

G

2.8.7

H

2.8.1

J

2.8.8

L

2.6

TABLE 4 Which element in Table 4 are metal and non-metal? Metal

: ..........................................................................................................................

Non- metal

: ........................................................................................................................... [2 marks]

State an element that exist as monoatomic gas.Explain your answer. .....…………………………………………………………………………………………........................

(c)

..……………………………………………………………………………………………....................... [2 marks] Write the formula for the ion formed from an atom of element L.

(d)

..................................................………………………………………………………………................ [1 mark] Element F reacts with element G to form a compound (i)

State the type of bond present in this compound.

(ii)

........................................................................................................................................... [1 mark] State two physical properties of compound formed.

………………………………………………………………………………………............ ………………………………………………………………………………………............ Set 1

4

Set 1

Chemistry Perfect Score Module 2007 [2 marks] (e)

When element H is burnt in G gas , H burns rapidly and brightly with a yellow flame and liberates white fumes. (i)

Suggest the name of the white fumes. ........................................................................................................................................... [1 mark]

(ii)

Write the equation for the reaction between element H and G gas.

...........................................................................................................................................

[2 marks] 5 Table 5 shows the electron arrangement for six atom , Q ,R ,T,W,X and Y. Electron

Atom

arrangement

Q

2.4

R

2.6

T

2.8

W

2.8.1

X

2.8.7

Y

2.8.8.1 TABLE 5

(a)

By using symbols and information in the table 5 , choose one atom that formed cation.

(b)

............................................................................................................................................................ [1 mark] Atom Q and atom X react to form a compound.

(c)

(i)

Write the formula of compound formed.

(ii)

.................................................................................................................................................... [1 mark] State one physical property of the compound.

(i)

.................................................................................................................................................... [1 mark] Compare the size of atom W with atom X. .................................................................................................................................................... [1 mark]

(ii)

Explain your answer in (c)(i). .................................................................................................................................................... .................................................................................................................................................... ....................................................................................................................................................

Set 1

5

Set 1

Chemistry Perfect Score Module 2007 [2 marks] (d)

(i)

Element T is not chemically reactive.Explain. .................................................................................................................................................... .................................................................................................................................................... [2 marks] State the position of element T in the Periodic Table.

(ii)

.................................................................................................................................................... [1 mark]

6

Graph 6 shows the temperature against time of solid substance X when heated. Substance X is an organic compound and flammable. 0

Temperature / C

S

Q

R

80

P Time/s 3

0

GRAPH 6

36

0

(a) Draw a diagram of the set-up of the apparatus used to determine the melting point of substance X.

[ 2 marks] (b) (i)

(ii)

State the melting point of substance X ........................................................................................................................................................ [ 1 mark] What is the state of matter of substance X at : PQ : ..................................................................................................................................................... RS : .................................................................................................................................................... [ 2 marks]

Set 1

6

Set 1

Chemistry Perfect Score Module 2007 (iii) Explain why the temperature remains constant from Q to R. ............................................................................................................................................................... ............................................................................................................................................................... [ 2 marks] (iv) State how the movement of substance X particles changes between R and S during heating. ……………………………………………………………………………………………………………………. [ 1 mark]

(c) If substance X is cooled to the room temperature without stirring, draw the graph of temperature against time obtained.

[ 2 marks] (d) Identify subtance X ..................................................................................................................................................................... [ 1 mark]

Set 1

7

Set 1

Chemistry Perfect Score Module 2007

7

Lactic acid is an acid produced in milk by bacteria that causes the milk to taste sour. Table 7 shows the percentage of composition by mass of each element in lactic acid.

Element

Percentage

Carbon

40.00

Hydrogen

6.67

Oxygen

53.33 TABLE 7

(a) Based on the information above, calculate the empirical formula of lactic acid. Given that the relative atomic mass of H = 1 ; C = 12 ; O = 16

[ 3 marks] (b) Relative molecular mass of lactic acid is 90. Determine the molecular formula of lactic acid.

[ 2 marks] (c) Calculate the number of hydrogen atom in 1 mol of lactic acid? 23 -1 Given that Avogadro number ,NA = 6.02 × 10 mol

[ 1 mark] (d) Calculate the number of moles of 4.5 g lactic acid. Given that the relative atomic mass of H = 1 ; C = 12 ; O = 16

[ 1 mark] (e) Vinegar or ethanoic acid has a similar empirical formula with lactic acid. (i) Given that three molecules of ethanoic acid have the same mass as two molecules of lactic acid. What is the relative molecular mass of ethanoic acid?

[ 1 mark] (ii) Determine the molecular formula of ethanoic acid.

Set 1

8

Set 1

Chemistry Perfect Score Module 2007 [ 2 marks]

8

Table 8 shows formula of four ions. Name of ions

Silver ion

Formula of ions

Zinc ion

+

2+

Ag

Zn

Nitrate ion

Chloride ion

NO3

Cl

-

TABLE 8 (a) Write the formula for each compound below : (i)

Silver nitrate

………..…..........................................................................................

(ii) Zinc chloride

: .......................................................................................................

(iii) Silver chloride

: .......................................................................................................

(iv) Zinc nitrate

: .......................................................................................................

[4 marks] (b) When silver nitrate solution is added to zinc chloride solution, white precipitate, silver chloride and zinc nitrate solution are formed. (i)

Identify the reactants and products of the reaction. Reactants : ........................................................................................................................

(ii)

Products : ........................................................................................................................ [2 marks] Write the chemical equation for the reaction occurs in (b).

........................................................................................................................................... [1 mark] (c) The following equation shows the decomposition of silver nitrate by heat. 2AgNO3

2Ag

+ 2NO2

+

O2

If 85.0 g of silver nitrate is heated completely, calculate : (i)

the mass of silver formed. Given that the relative atomic mass of N =14; O = 16; Ag =108

3 marks] (ii)

the volume of oxygen gas formed at room conditions. 3 Given that the Molar volume : 24 dm at room conditions

[ 2 marks] Set 1

9

Set 1

Chemistry Perfect Score Module 2007

PAPER 2 – ESSAY SECTION B 9

(a)

The volume of 2.2 g of carbon dioxide gas is less than the volume of 2.2 g of hydrogen at the same temperature and pressure. Explain the above statement. –1

Given that relative molecular mass of carbon dioxide = 44 g mol , –1 relative molecular mass of oxygen = 2 g mol [3 marks] (b)

(i)

What is meant by empirical formula?

[ 1 mark]

(ii)

Describe an experiment in the laboratory to determine the empirical formula of magnesium oxide. Your answer should consist of the following.  Procedures of the experiment  Calculation involved  Precautions need to be taken Given that relative atomic mass of Mg = 24, O = 16 [13 marks]

(c)

Magnesium can reduced copper oxide to copper. Explain why the empirical formula of the copper oxide cannot be determined by heating the mixture of copper oxide and magnesium powder. [ 3 marks]

PAPER 2 - ESSAY SECTION C 10

Table 7 shows the proton number of atoms P, Q and R. Element

Proton number

P

8

Q

12

R

17

TABLE 7 (a) Based on electron arrangement, explain the formation of chemical bond between (i)

element P and element P

[5 marks ]

(ii)

element Q and element R

[7 marks ]

(b) Gas P reacts with element Q to produce a white solid. (iii) (ii)

Write a chemical equation for the reaction between gas P and element Q. State three physical properties of the white solid. [ 4 marks ]

(c) What is the position of elelment Q in the Periodic Table of the elements? Explain how do you obtain your answer. [ 4 marks ] Set 1

10

Set 1 PAPER 3

Chemistry Perfect Score Module 2007

12. The diagram below shows the apparatus set-up for the experiment to determine the freezing point of substance X.

thermometer

Retort stand Substance X Volumetric flask

The diagram below shows the thermometer reading for the cooling of substance X at certain time intervals.

95

90

90

90

90

85

85

85

85

80

80

80

2nd Minute

3rd minute

1st minute

0 Minute

90

90

80

75

85

85

75

70

80

70

65

4th minute (a)

6th minute

5th minute

7th Minute

Record the thermometer readings shown in the diagram above by completing the table below. time/minute

0

1

2

3

4

5

6

7

o

Temperature/ C [3 marks] Set 1

11

Set 1

Chemistry Perfect Score Module 2007 (b)

Draw the graph of temperature against time on the graph paper provided.

(c)

Based on the graph in (b), (i)

State the change in temperature of substance X for the whole experiment. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... [3 marks]

(ii)

State the inference for your answer in (c) (i) . ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... [3 marks]

(d)

What is the freezing point of substance X? Show and label it on the graph how you obtained the answer. …………………….............…………………………………………………………… [3 marks]

(e)

Based on this experiment, what is meant by freezing point? ……...………………………………………………………………………………… ……...………………………………………………………………………………… ……...………………………………………………………………………………… [3 marks]

(f)

o

If substance X is heated from room temperature until 100 C, what is the temperature when substance X starts to melt? Explain your answer. …………………………………………………………………………………....................... [3 marks]

Set 1

12

Set 1 12

Chemistry Perfect Score Module 2007 Elements in Group 1 of the Periodic Table of Elements can be arranged based on the reactivity of the elements with water. An experiment is carried out to investigate the statement above. The table below shows the apparatus set up and the observations for the experiment to determine the reactivity of the Group 1 elements based on their reactions with water. Apparatus set-up

Observation towards the metal

Lithium

))

water

Lithium moves slowly on the surface of the water with a “hiss” sound.

Potassium

)) )))) )

water

Potassium moves vigorously and randomly on the surface of the water with a “hiss” sound.

sodium

)) )

water

Sodium moves quickly and randomly on the surface of the water with a “ hiss” sound.

(a) State the variables that are involved in the experiment. Name of variables Action to be taken (i) Manipulated variable: (i) The way to manipulate variable: ……………………………………..

………………………………………..

……………………………………..

………………………………………...

(ii) Responding variable:

(ii) What to observe in the responding variable: ………………………………………..

…………………………………… ………………………………………..……… …………………………………… (iii) Controlled variable:

(iii) The way to maintain the controlled variable:

……………………………………..

………………………………………

……………………………………..

……………………………………… [6 marks]

Set 1

13

Set 1

Chemistry Perfect Score Module 2007 (b)

State one hypothesis for the experiment. ……………………………………………………………………………………… ……………………………………………………………………………………… [3 marks]

(c)

Based on the observations in the figure above, arrange lithium, potassium and sodium in the descending order of reactivity of metals towards water.

Descending order of reactivity of metals towards water. [3 markah] (d)

Solution X was produced from the reaction of sodium with water. Classify the ions that exist in solution X into positive ions and negative ions. Positive Ions

Negative Ions

[3 marks] 3

“When lithium metal is put in water, it moves very slowly on the surface of the water. When sodium metal is put in water, it moves quite fast and produces “hiss” sound. When potassium metal is put in water, it moves very fast and produces small explosions”. Metal

Water

Plan an experiment in the laboratory to investigate the reactivity of lithium, sodium and potassium with water and describe the effect of the solution produced towards a red litmus paper. The planning of your experiment must consist of the following: (a) Aim of experiment (b) Statement of the hypothesis (c) All the variables (d) List of substances and apparatus (e) Procedure of the experiment (f) Tabulation of data [17 marks]

Set 1

14

Set 1

Chemistry Perfect Score Module 2007

Sample Answer Section A 1

(a)

Formula that shows the simplest ratio of the number of atoms for each element in the compound.

1

Oxide of copper

(b) Dry hydrogen gas

Heat Functional diagram an heating is shown Dry hydrogen gas and oxide of copper are labelled (c)

Cu

O

24.46 – 19.60 / 4.86 4.86 64

/ 0.076

25.68 – 24.46 / 1.22

1

1.22 / 0.076 16

1

CuO

2

1 1

1

(d)

CuO + H2  Cu + H2O

1

(e)

Collect the gas in a test tube Put lighted wooden splinter at the mouth of the test tube No pop sound

1 1 1

(f)

No Aluminium more reactive than hydrogen // Hydrogen less reactive than aluminium // hydrogen below aluminium in reactivity series.

1

(a)

(i) (ii)

(b)

(i) (ii)

1 12

The proton number is the number of protons in an atom 1 The nucleon number is the total number of protons and neutrons in an atom 1 Isotopes are atoms of the same element with different numbers of neutrons 1 X and Y 1

(c)

The number of proton = 11 The number of electron = 11 The number of neutron = 12

1 1 1

(d)

2.8.7

1

(e)

1 Set 1

15

Set 1

Chemistry Perfect Score Module 2007 (f)

(i) (ii)

(g)

The electrons in the outermost occupied shell 1 35 X 17

3

(a) (b)

(c)

(d)

2.8.8 (i) (ii)

1 1

1 12

Z Achieve octet electron arrangement / / achieve 8 electron in the outermost shell // 8 valence electron

1 1 1

(i)

W

1

(ii)

The atomic size of W is bigger than the atomic size of V The attraction between the nucleus and the valence electron is weaker in an atom W It is easier for atom W to donate / release electron

1

High melting / boiling point// dissolve in water// do not dissolve in organic solvents // conduct electricity in aqueous solution or molten state .

1 1

1

(e)

Y

Y

X

Y

Y

Correct number of atoms( 4 of atom Y and 1 of atom X) Correct number of shells and electrons

Set 1

16

1 1 10

Set 1

Chemistry Perfect Score Module 2007

4(a)

Metal : H Non- metal : E, F, G, J , L J 8 electron in the outermost shell // achieve octet electron arrangement 2L Covalent bond. Low melting/boiling point// do not dissolve in water// dissolve in organic solvents // do not conduct electricity in aqueous solution or molten state . [ Any two ] Sodium chloride. 2H + G2 2HG Total

4(b) 4(c) 4(d)(i) 4(d)(ii)

4(e)(i) 4(e)(ii)

5

(a) W / Y (b) (i) (ii)

(c) (i) (ii)

d) (i)

(ii)

1 1 1 1 1 1 1 1

1 1 10

1 QX4

1

Low melting/boiling point// do not dissolve in water// dissolve in organic solvents // do not conduct electricity in aqueous solution or molten state . [ Any one ]

1

The atomic size of X is smaller than the atomic size of W

1

The number of proton of atom X more than atom W The attraction by the nucleus on the electrons in the first three occupied shells in atom X become stronger

1

Have eight valence electrons//achieve octet electron arrangement

1

No need to lose , gain or share electrons with atom of another element

1

Group18 and period 2

1

1

9

Set 1

17

Set 1 6

Chemistry Perfect Score Module 2007 (a) Thermometer

Boiling tube Water Substance X Bunsen burner

(b) (i) (ii)

(iii)

(iv) (c)

[Functional diagram ] [ Labels :  X, water, thermometer, Bunsen burner/heat ]

1

80 oC

1

PQ : solid RS : liquid

1

[1 + 1]

2

The energy absorbed is used to overcome the forces of attraction between the particles

1

The particles move faster

1

Temperature / 0C

80

Time/s [The shape of the graph is correct ] [ Both axis are labeled with unit ]  x-axis : time/s , y-axis : temperature/ 0C  80 0C on graph (d) Set 1

naphthalene

…1

…1

2 1 10

18

Set 1 7

Chemistry Perfect Score Module 2007 (a) Element

C

Number of moles (mol)

H

O

40.00 12

6.67 1

53.33 16

= 3.33

= 6.67

= 3.33

1

2

1

Ratio of moles

1

1

The empirical formula of the compound is CH2O (b)

n [ 12 + 2(1) + 16 ] n

1

= 90 =

90 30

1

= 3

(c)

(d)

Molecular formula of lactic acid is C3H6O3

1

One molecule of lactic acid contains 6 hydrogen atoms  1 mol of lactic acid contains 6 mol of hydrogen atoms 23  1 mol of lactic acid contains 6 × 6 .02 × 10 hydrogen atoms

1

The number of mole of lactic acid

=

4.5 90

1

= 0.05 mol (e)

3 × Mr of ethanoic acid = 2 × Mr of lactic acid Mr of ethanoic acid =

2 x 90 3

= 60

(f)

n (30) n

1

= 60 = 2

1

Molecular formula of ethanoic acid is C2H4O2 / CH3COOH

8

(a) (i) (ii) (iii) (iv)

AgNO3 ZnCl2 AgCl Zn(NO3)2

1 1 1 1

(b) (i)

Silver nitrate and zinc chloride

1

Silver chloride and zinc nitrate

1

(ii) (c) (i)

2AgNO3

+ ZnCl2

Number of moles of AgNO3

2AgCl =

+Zn(NO3)2

1

85 170

= 0.5 mol 2 moles of AgNO3 produce 2 moles of Ag Set 1

1 10

19

1

Set 1

Chemistry Perfect Score Module 2007 0.5 mole of AgNO3 produce 0.5 mole of Ag Mass of Ag

(ii)

1

= 0.5 × 108 = 54 g

1…….…3

2 moles of AgNO3 produces 1 mole of O2 0.5 mole of AgNO3 produces 0.25 mole of O2 Volume of O2

1

= 0.25 × 24 3 = 6 dm

1…….…2 10

SECTION B 9

(a) Number of mole of carbon dioxide =

Number of mole of hydrogen

=

2 .2 = 44 2 .2 2

0.05 mol

= 1.1 mol

1

The number of mole of carbon dioxide is smaller; therefore, its volume is smaller than the volume of hydrogen (b) (i)

(ii)

        

1

1

The empirical formula of a compound is the simplest whole number ratio of atoms of each element present in the compound. 1 [ Material and apparatus ] [Magnesium ribbon, sand paper, crucible with lid, tongs, Bunsen burner, tripod stand, pipe-clay triangle and balamce.] or [diagram] 2 [ Procedure] A crucible and its lid is weighed and its weight is recorded. A 10 cm length of magnesium ribbon is coiled loosely and is placed in the crucible. The crucible with its lid and content are weighed again and the weight is recorded . The crucible is heated strongly without its lid. When the magnesium starts to burn, the crucible is covered with its lid. Using a pair of tongs, the lid is lifted at intervals. When the burning is completed, the lid is removed and the crucible is heated strongly for 2 minutes. The rucible is allowed to cool to room temperature. The crucible and its lid and content are weighed again and its weight is recorded.

1 1 1 1 1 1 1 1 max 5

  

[Precautions taken] The magnesium ribbon is cleaned with sand paper to remove the layer of magnesium oxide on the surface. The crucible must cover with its lid to prevent the white fumes of magnesium oxide of escaping. The processes of heating, cooling and weighing are repeated until a constant mass is obtained. [any two of the above] [ Results ]  Crucible + lid Crucible + lid + magnesium Crucible + lid + magnesium oxide [ Calculation ]

Set 1

20

= a g = b g = c g

2

1

Set 1

Chemistry Perfect Score Module 2007 Element Mass(g) Number of moles of atoms Simplest ratio of moles

Magnesium b-a b-a/24

Oxygen c-b c-b/16

X

y 2 1

Empirical formula = MgxOy (c)

1 2 3

Unable to make sure that all the magnesium is oxidised . The products (Cu and MgO) cannot be separated. The mass of copper and oxygen cannot be determined.

1 1 1 Total 20

1. 2. 3. 4. 5.

Two atoms of P combine through covalent bond. 1 Each atom of P needs two more electrons to achieve octet electron arrangement. Each atom of P contributes two electrons to each other for sharing. 1 Two atoms of P share two pairs of electrons. 1 A double covalent bond is formed.

SECTION C 10

(a)(i)

P

P

2 (ii)

1. 2. 3. 4. 5.

Atom Q and atom R combine through ionic bond. 1 To achieve octet electron arrangement, 1 2+ atom Q with 6 valence electrons loses two electrons to form Q ion 1 Two atom R, each atom with 7 valence electrons gains one electron to form R ion. 1 2+ Q ion and R ion are attracted to each other by strong electrostatic force.1

_

R

2+

Q

_

R

2 (b)(i) 2Q + P2 (ii)

(c)

Set 1

2QP

1

1. 2. 3.

Have high melting point Usually soluble in water Conduct electricity in the molten state or aqueous solution.

1 1 1

1. 2. 3. 4.

Element Q is located in Group 2 because it has two valence electrons Element Q is located in Period 3 because it has three shells occupied with electrons

1 1 1 1

21

Set 1 1

Chemistry Perfect Score Module 2007 (a) To measure using numbers.

Score 3

Explanation Able to record all the readings correctly to 1 decimal place. Time (minute) Temperature o ( C)

0

1

2

3

4

5

6

7

95.0

89.0

84.5

83.0

83.0

83.0

77.0

70.0

(b) Communication Score 3

Explanation Able to draw the graph with the following elements::

   

Set 1

o

X-axis is labeled(minute) and y-axis temperature( C) with consistent scales Size of the graph is at least half the page of the graph paper. All the points are plotted correctly Curve of the graph is correct and smooth

22

Set 1

Chemistry Perfect Score Module 2007

Graph of temperature against time Temperature/oC

Melting point

Time/minute

Set 1

23

Set 1

Chemistry Perfect Score Module 2007

(c) (i) the relationship of space and time Score 3

Explanation Able to explain the change of temperature with time from the graph. Suggested answer:

  

In the first 3 minutes, the temperature of substance X will decrease from o o 95 C to 83 C. o

Constant temperature at 83 C for 3 minutes. o

The temperature decreases again after 83 C

(c) (ii) Inference Score 3

Explanation Able to make the correct inference. Suggested answer:

  

Temperature decreases because heat is released to the surrounding. Temperature is contant because heat released to the surrounding is balanced by the heat released when bonds are formed. o

The freezing process is at 83 C // solid and liquid X exist together

1(d) Data analysis Score

3

Explanation

  

Able to state the freezing point accurately based on the graph with the correct unit. Dotted line is shown on the graph. Labeling the freezing point at temperature axis.

1(e) Operational definition Score Explanation 3 Able to give the meaning of freezing point accurrately. Suggested answer: o Freezing point is the constant temperature at 83 C even though substance X is let to cool to room remperature.

1(f) To predict Score Explanation 3 Able to predict the melting point of substance X accurrately with unit and with correct reasons. Suggested answer : o 83.0 C Value of melting point substance X is the same as its freezing point.

Set 1

24

Set 1

Chemistry Perfect Score Module 2007

2(a) To control the variables Score Explanation 6

Able to predict the manipulated variable, the responding variable and the constant variable completely. Suggested answer: Manipulated variable : metals of Group 1 elements // sodium, lithium, potassium. Responding variable: the reactivity of the reaction with water // the speed of movement on the water surface Constant variable: size/mass of metals. Volume of water

2(b) To make hypothesis Score 3

Explanation Able to state how to control the manipulated variables correctly Suggested answer: Repeat the experiment by using the metals of sodium, lithium and potassium Able to state correctly the way to control the manipulated variable Suggested answer: To observe how fast the metals move on the surface of water. Able to use the metal granules with the same size Suggested answer : Use the metal granules with the same size.

Explanation

Able to state the relationship between the manipulated variable and the responding variable correctly. Suggested answer: The reactivity of Group 1 elements increases going down the group.

2(c) To interprete data Score Explanation 3 Able to arrange correctly the reactivity series of the metals according to descending order. Answer: potassium, sodium, lithium 2(d) To classify Score 3

Set 1

Explanation Able to classify the ions correctly. [to name or write all the formula of the ions correctly at the cations and anions group.] + + Answer: positive ion/ cation : sodium ion/ Na , hydrogen ion/ H Negative ion/anion : hydroxide ion/ OH

25

Set 1

Chemistry Perfect Score Module 2007

No 3(a)

Explanation [Able to state the aim of experiment accurately] To compare the reactivity of lithium, sodium and potassium based on the reaction with water and describing the effect of the solution towards the red litmus paper.

3(b)

Hypothesis Metals of lithium, sodium and potassium show different rate of reactivity with water and the solution formed turns red litmus paper to blue.

3(b)

Variables a) Manipulated variable :type of metals b) Responding variable : reactivity of reaction c) Constant variable : water and temperature

Score 3

3 x1 2x1 1x1

3(c )

[Able to list the correct and complete substances and apparatus.] Substances and Apparatus Lithium, sodium and potassium metals with water, basin, knife, forceps, blue litmus paper and white tile.

3

3(d)

[Able to give all the procedures correctly, steps 1 - 7] 1. Lithium metal is cut into a small piece 2. The paraffin oil on the surface of the metal is wiped with the filter. 3. A basin is filled with water. 4. Lithium metal is put on the surface of the water with a pair of forceps. 5. Reactivity of the reaction is observed and recorded. 6. The experiment is repeated with sodium and potassium metals.

3

3(e)

[Able to show the accurate tabulation of data with correct title.] Metals Lithium Sodium Potassium

Set 1

Observations

26

3