f4 chapter 2&3 strucutre q

Answer To Score Chemistry Form 4 Chapter 2 The Structure of The Atom Chapter 3 Chemical Formulae and Equation

FORM 4 CHAPTER 2 THE STRUCTURE OF THE ATOM & CHAPTER 3 CHEMICAL FORMULAE AND EQUATION

ANALYSIS OF PAST YEAR QUESTIONS FROM 2003 – 2008Year 2003 2004 2005 2006 2007 2008

Paper No.

P2 P3 P2 P3 P2 P3 P2 P3 P2 P3 P2 P3

Type of question

S E S E S E S E S E S E S E S E S E S E S E S E

Question No

1 1 1a 110a10b

1 2 9 3,5 8 3

STRUCTURED QUESTION

1 SPM 2003 /P2/ Q1Figure 1 shows the set-up of apparatus for an experiment to determine the empirical formula of magnesium oxide.

Figure 1Result :Mass of crucible + lid = 24.0 gMass of crucible + lid + magnesium ribbon = 26.4 gMass of crucible + lid + magnesium oxide = 28.0 g

(a) What is meant by empirical formula?

………………………………………………………………………………………………

………………………………………………………………………………………………[1 mark]

(b) Based on the above results,(i) Calculate the mass of magnesium and the mass of oxygen that have reacted.

[1 mark]

(ii) Calculate the mole ratio of magnesium atoms to oxygen atoms

1


[Relative Atomic Mass: O = 16, Mg = 24]

[1 mark]

(iii) Determine the empirical formula of magnesium oxide.

[1 mark]

(iv) Write the chemical equation for the reaction in this experiment.

………………………………………………………………………………………………[1 mark]

(c) Why was the crucible lid opened once in a while during the experiment?

……………………………………………………………………………………………

……………………………………………………………………………………………[1 mark]

(d) Metal X is placed below hydrogen in the reactivity series. You are required to carry out an experiment to determine the empirical formula of the oxide of metal X. The apparatus provided are combustion tube, glass tube, cork, Bunsen burner, and porcelain dish.

(i) Draw a labeled diagram of the set-up of the apparatus for the experiment.

[2 marks]

(ii) Describe the steps that should be taken to ensure that all the air in the combustion tube has been expelled.

2


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

……………………………………………………………………………………………

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

2 SPM 2004/ P2/ Q1(a) Table 2 shows four substances and their respective formulae

Substance Chemical formulaIodine I2

Copper CuNaphthalene C10H8

Copper (II) sulphate CuSO4

Table 2Use information from Table 2 to answer the following equations

(i) State one substance from Table 2 which exists as a molecule.

………………………………………………………………………………………………[1 mark]

(ii) Which substance has the highest melting point, iodine, copper or naphthalene?

………………………………………………………………………………………………[1 mark]

(iii) What is the state of matter of copper (II) sulphate at room temperature?

………………………………………………………………………………………………[1 mark]

(iv) State the substance in Table 2 which can conduct electricity in the solid state.

………………………………………………………………………………………………[1 mark]

(v) Draw the arrangement of particles in the substance in (a)(iv)[1 mark]

(vi) Write the ionic formula for the substance in (a)(iv).

………………………………………………………………………………………………[1 mark]

(b) Graph 2.1 shows the temperature against time when solid naphthalene is heated

3


Graph 2.1(i) State the melting point of naphthalene.

…………………………………………………………………………………………………[1 mark]

(ii) Explain why there is no change in temperature from Q to R

…………………………………………………………………………………………………

…………………………………………………………………………………………………

…………………………………………………………………………………………………[2 marks]

(iii) State how the movement of naphthalene particles changes between R and S during the heating.

…………………………………………………………………………………………………

…………………………………………………………………………………………………[1 mark

3 SPM 2006/ P2/ Q2(i) What is the chemical symbol used to represent one water molecule?

………………………………………………………………………………………………[1 mark]

(ii) What is the name of the isotope of an element used as a standard in determining relative atomic mass?

………………………………………………………………………………………………[1 mark]

b(i) What is the mass of 6.0dm3 of carbon dioxide gas, CO2 at standard temperature and pressure?[1 mole of gas occupies 24 dm3 at standard temperature and pressure;Relative atomic mass for CO2 = 44]

[2 marks]4


(ii) How many molecules are there in 6.0 dm3 of carbon dioxide gas?[Avogadro number = 6.02 x 1023]

[1 mark]

(iii) Explain briefly the relationship between the volume, mass and the number of molecules of carbon dioxide in 3b(i) and 3b(ii) at stansard temperature and pressure.

………………………………………………………………………………………………

………………………………………………………………………………………………

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

4 SPM 2007 / P2/ Q3(a) What is the meaning of empirical formula?

………………………………………………………………………………………………

………………………………………………………………………………………………[1 mark]

(b) Diagram 3.1 shows an incomplete equation which is one of the steps involved in determining the empirical formula.Complete this equation.

Diagram 3.1[1 mark]

(c) Diagram 3.2 shows the apparatus set-up for two methods used to determine the empirical formula of two compounds.

Diagram 3.2

5

Mass = Relative atomic mass …………………………………………………..


Based on Diagram 3.2, determine the values of the following:[Relative atomic mass : O=16, Pb = 207 ]

(i) Mass of lead

= …………………………………..g[1 mark]

(ii) Number of moles of lead

= …………………………………..g[1 mark]

(iii) Mass of oxygen

= …………………………………..g[1 mark]

(iv) Number of moles of oxygen

= …………………………………..g[1 mark]

(v) Empirical formula of lead oxide

= ………………………………………………………….[1 mark]

5 SPM 2007 / P2/ Q5Diagram 5 shows the symbols of the atoms of element X and element Y.The letter used are not the actual symbols of the elements.

Diagram 5

(a) State the proton number of the atom of element X.

………………………………………………………………………………………………[1 mark]

b(i) F4 Topic 4 : Periodic TableIdentify the position of element X in the Preiodic Table of Elements

………………………………………………………………………………………………[1 mark]

b(ii) Explain why element X is placed at the position identified in 5(b)(i).

………………………………………………………………………………………………

………………………………………………………………………………………………[1 mark]

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c(i) F4 Topic 4 : Periodic TableThe reaction between element X and oxygen is less reactive than the reaction between element Y and oxygen.Explain this using ideas about valence electron.

………………………………………………………………………………………………

………………………………………………………………………………………………[2 marks]

(ii) Draw a labeled diagram to show the apparatus set-up that can be used to determine the reactivity of the reaction between element X or element Y and oxygen gas.

[ 2marks]

(d) 2.3g of element X reacted completely with oxygen.The following equation represents the reaction.

4X(s) + O2(g) 2X2O(s)

[Relative atomic mass : X = 23, O = 16]

(i) Calculate the number of moles of element X.

[1 mark]

(ii) Calculate the maximum mass of X2O formed.

[3 marks]

7


6 SPM 2008 / P2/ Q3(a) Diagram 3.1 shows the results of an experiment to investigate the movement of

bromine particles in air.

Diagram 3.1

(i) State the name of the process involved in this experiment.

………………………………………………………………………………………………[1 mark]

(ii) State the type of particle present in bromine gas, Br2.

………………………………………………………………………………………………[1 mark]

(iii) Explain the observation in this experiment based on the kinetic theory of matter.

………………………………………………………………………………………………

………………………………………………………………………………………………

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

(iv) This experiment is repeated at a higher temperature.Predict the time taken for the bromine vapour to spread throughout the space in both gas jars.

………………………………………………………………………………………………[1 mark]

8

Bromine vapour spreads throughout both gas jars within 10 minutes

Gas jarAir

cover

Cover removed

Bromine vapour


(b) Diagram 3.2 shows two balloons containing oxygen gas and carbon dioxide gas respectively.

Balloon A Balloon B

Diagram 3.2Based on the given information:

(i) Calculate the mass of oxygen gas in balloon A[Relative atomic mass : O = 16]

[1 mark]

(ii) Calculate the volume of carbon dioxide gas in balloon B.[Molar volume of gas = 24 dm3 mol-1 at room temperature and pressure]

[1 mark]

(iii) Compare the number of gas molecules in balloon A and in balloon B.Explain your answer.

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………[2 marks]

9

0.5 molCarbon dioxide gas, CO2

0.5 mol oxygen gas, O2


7 SPM 2004/ P3/ Q1A student carried out an experiment to determine the empirical formula of magnesium oxide. The steps and set-up of apparatus of the experiment are shown in Figure 1.

(a) Complete the following table by stating the observation and related inferences in the experiment.

Observation Inferences

(i) ………………………………………..

……………………………………….

(ii) ……………………………………….

……………………………………….

(i) ………………………………………….

………………………………………….

(ii) …………………………………………

…………………………………………….[6marks]

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(b) Record the reading to two decimal places for:

The mass of crucible and lid: ………………………………g

The mass of crucible, lid and magnesium ribbon : ……………………………g

The mass of crucible, lid and magnesium oxide when cooled : …………………….g[3marks]

ci) What is the mass of magnesium that has been used?

[3marks](ii) What is the mass of oxygen which reacted with magnesium?

[3marks](iii Determine the empirical formula of magnesium oxide

Use the information that the relative atomic mass, Mg = 24 and O = 16.

[3marks](d) Based on your answer in (c)(iii), how many moles of magnesium and oxygen atoms

have reacted?

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

8 SPM 2005 /P3/ Q1An experiment is carried out to determine the freezing point of naphthalene. Solid naphthalene is heated in a water bath until it melts completely.The initial temperature is recorded.Then molten naphthalene is left to cool.The reading of the temperature is recorded every 30 seconds.Figure 1 shows the recorded thermometer readings at 30 seconds intervals.

11


a) Record the temperatures in the space provided in Figure 1.[3marks]

b) On the graph paper below, draw the graph of temperature against time for the cooling of naphthalene.

12


[3marks]

ci) Use the graph in (b), to determine the freezing point of naphthalene.Show on the graph how you determine this freezing point.

[3marks](ii) How does the graph in (b) show the freezing point of naphthalene?

………………………………………………………………………………………………

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

13


(d) The temperature of naphthalene did not change from the 90th second until the 50th second during the cooling process.Explain why.

……………………………………………………………………………………………….

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

(e) On the graph paper below sketch the curve you would expect if the molten naphthalene is cooled quickly.

[3marks]

(f) Naphthalene is an example of a covalent compound and sodium chloride is an example of an ionic compound.Classify the following into covalent or ionic compounds.

[3marks]

14

Glucose, potassium iodide, copper(II) sulphate,Aluminium oxide, tetrachloromethane, ethanol

f4 chapter 2&3 strucutre q

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