HKDSE Chem FX ExamS5 2011 Set1 Eng

HONG KONG DIPLOMA OF SECONDARY EDUCATION EXAMINATION

CHEMISTRY SECONDARY FIVE EXAMINATION PAPER

Name Class Class no.

(SET 1) Time allowed: 2 hours 30 minutes This paper must be answered in English.

INSTRUCTIONS

Section B

1. There are TWO sections, A and B, in this Paper. Section A carries 36 marks and Section B carries 84 marks.

2. Section A consists of multiple-choice questions while Section B contains conventional questions.

3. Answer ALL questions.

4. All multiple-choice questions carry equal marks.

5. You should mark only ONE answer for each multiple-choice question. If you mark more than one answer, you will receive NO MARKS for that question. No marks will be deducted for wrong answers.

Question No. 1 2 3 4 5 6 7 8 9 10 11 12 Total

Marks

Full Marks 8 − 7 − 7 − 6 − 7 − 5 − 7 − 9 − 7 − 8 − 5 − 8 − 8 4

6. A Periodic Table is printed on the back of this question paper. Atomic numbers and relative atomic masses of elements can be obtained from the Periodic Table.

COMMON PHYSICAL CONSTANTS Avogadro constant (L) = 6.0 × 10 mol 3 –1 Molar volume of gas at s.t.p. = 22.4 dm mol 3 Molar volume of gas at room conditions = 24.0 dm –1 mol 23

HKDSE CHEMISTRY S5 Exam Paper (Set 1) © Aristo Educational Press Ltd. 2011

–1

CHEMISTRY 1

Section A (Multiple-choice Questions) Answer ALL questions. Choose the best answer for each question. PART I 1.

The percentage by mass of the three most abundant elements on the Earth’s crust increases in the ascending order: A. Aluminium, Silicon, Oxygen B. Oxygen, Silicon, Aluminium C. Oxygen, Aluminium, Silicon D. Silicon, Oxygen, Aluminium

2.

Which of the following diagrams represents a mixture of elements? A. B. C. D.

3.

Which of the following statements concerning the formation of magnesium ions from magnesium atoms is correct? A. The atomic number of magnesium decreases by 1. B. The mass number of magnesium decreases by 1. C. The charge of magnesium increases by 1. D. The number of shells occupied by electrons in a magnesium atom decreases by 1.

4.

Silicon carbide has a structure similar to that of diamond. Which of the following statements concerning silicon carbide is correct? A. It can be used as a cutting tool. B. It can be used as a lubricant. C. It can be used as jewellery. D. It is a good conductor of electricity.

5.

An oxide of iodine, X, reacts with carbon monoxide as shown in the equation below: X + 5CO → I2 + 5CO2 Which of the following is the correct formula of X? A. I2O B. IO2 C. IO5 D. I2O5

6.

Which of the following processes would NOT produce hydrogen gas? A. Adding calcium to water B. Adding copper to dilute sulphuric acid C. Adding magnesium to dilute hydrochloric acid D. Passing steam over red hot iron


CHEMISTRY 2

7.

Consider the following reaction: Ba(NO3)2(aq) + H2SO4(aq) → 2HNO3(aq) + BaSO4(s) Which of the following ions are the spectator ions? (1) Ba2+ (2) H+ (3) SO42– (4) NO3– A. (1) and (3) only B. (1) and (4) only C. (2) and (3) only D. (2) and (4) only

8.

What is the percentage by mass of carbon in glucose, C6H12O6? A. 6.7% B. 25% C. 40% D. 60%

9.

A white solid is found near the rim of a reagent bottle containing sodium hydroxide solution. The white solid is likely to be A. sodium oxide. B. sodium carbonate. C. sodium hydrogencarbonate. D. sodium hydroxide.

10. A sample of concentrated hydrochloric acid has a density of 1.21 g cm−3 and contains 32.3% of HCl by mass. What is the concentration (correct to one decimal place) of hydrochloric acid in the sample? A. 3.9 M B. 10.3 M C. 10.7 M D. 14.3 M 11. Mosquitoes inject mild acid into the skin when they bite us. Which of the following substances should NOT be used to treat the affected area? A. Plain soap B. Soda C. Toothpaste D. Black coffee 12. Which of the following pieces of apparatus should be used when a standard solution is prepared from a pure liquid? (1) Pipette (2) Volumetric flask (3) Electronic balance A. (1) and (2) only B. (1) and (3) only C. (2) and (3) only D. (1), (2) and (3)


CHEMISTRY 3

13. A compound has the following structure:

Which of the following is the systematic name for this compound? A. 2-bromomethyl-2-chloro-2-methylethanol B. 3-bromo-2-chloro-2-methylpropan-1-ol C. 1-bromo-2-chloro-2-methylpropan-3-ol D. 1-bromo-2-chlorobutan-2-ol 14. Which of the following molecular formulae represents an alkanoic acid? A. CH2O B. CH2O2 C. C2H2O2 D. C2H6O2 15. Which of the following bonds is the least polar? A. P–F B. O–F C. Si–N D. B–Cl 16. Which of the following species is isoelectronic with that of carbonate ion? A. NO3– B. CH3+ C. SO32– D. PO43– 17. Consider the following chemical equation: x CH4(g) + y NO3–(aq) + 8H+(aq) → x CO2(g) + z N2(g) + 14H2O(l) Which of the following combinations is correct? x y z A. 2 6 3 B. 2 4 2 C. 5 8 4 D. 8 10 5 18. Which of the following chemical reactions involves the greatest change in the oxidation number of nitrogen? A. Mg + 2NO3– + 4H+ → Mg2+ + 2NO2 + 2H2O B. 2NO + O2 → 2NO2 C. N2 + O2 → 2NO D. N2 + 3H2 → 2NH3


CHEMISTRY 4

19. Which of the following equations shows the reaction occurred at the positive electrode of a silver oxide cell? A. Zn(s) → Zn2+(aq) + 2e– B. Zn(s) + 2OH–(aq) → ZnO(s) + H2O(l) + 2e– C. Ag2O(s) + H2O(l) + 2e– → 2Ag(s) + 2OH–(aq) D. Ag+(aq) + e– → Ag(s) 20. Which of the following conditions is NOT required in the definition of ‘standard conditions’? A. Temperature of 25°C B. Pressure of 101.3 kPa C. Concentrations of all solutions are 1.0 mol dm–3. D. All reactants and products are in their gaseous state. 21. Which of the following equations represents the standard enthalpy of formation for hydrogen iodide? A. H2(g) + I2(g) → 2HI(g) B. C. D.

1 1 H2(g) + I2(g) → HI(g) 2 2

H(g) + I(g) → HI(g) H+(g) + I–(g) → HI(g)

22. Consider the following reaction: 2NaHCO3(s) → Na2CO3(s) + CO2(g) + H2O(l) Given the following data: Standard enthalpy change of formation Compound NaHCO3(s) –948 kJ mol–1 Na2CO3(s) –1131 kJ mol–1 CO2(g) –395 kJ mol–1 H2O(l) –286 kJ mol–1 What is the enthalpy change for the reaction? A. +84 kJ mol–1 B. –84 kJ mol–1 C. –864 kJ mol–1 D. +864 kJ mol–1 Directions: Each question below (Questions 23 to 24) consists of two separate statements. Decide whether each of the two statements is true or false; if both are true, then decide whether or not the second statement is a correct explanation of the first statement. Then select one option from A to D according to the following table: A. Both statements are true and the 2nd statement is a correct explanation of the 1st statement. B. Both statements are true and the 2nd statement is NOT a correct explanation of the 1st statement. C. The 1st statement is false but the 2nd statement is true. D. Both statements are false.


CHEMISTRY 5

1st statement 23. Concentrated sulphuric acid can be used to dry any gas.

2nd statement Concentrated sulphuric acid has a high affinity for water.

24. Thermal decomposition of calcium carbonate is a redox reaction.

Calcium carbonate is converted into calcium oxide in the decomposition.

END OF PART I


CHEMISTRY 6

PART II 25. Consider the following compounds: (1) CH3CH2CH2SH (2) CH3CH2CH2OH (3) CH3CH2CH2CH3 What is the order of increasing boiling point of the compounds? A. (3) < (2) < (1) B. (1) < (2) < (3) C. (2) < (3) < (1) D. (3) < (1) < (2) 26. Which of the following compounds is the most soluble in water? A. Propane B. Propene C. Propan-1-ol D. Hexan-1-ol 27. Which of the following tests can be used to distinguish between CH3CH2CHO and CH3CH(OH)CH3? A. Heating with acidified potassium dichromate solution B. Adding phosphorus pentachloride C. Adding bromine (dissolved in tetrachloromethane) in darkness D. Adding cold acidified potassium permanganate solution 28. Consider the following equilibrium: CH4(g) + H2O(g) CO(g) + 3H2(g) ∆H = +206 kJ mol–1 Which of the following statements are correct when the temperature increases? (1) The equilibrium position shifts to the right. (2) The rates for both forward and backward reactions increase. (3) The forward reaction becomes exothermic. A. (1) and (2) only B. (1) and (3) only C. (2) and (3) only D. (1), (2) and (3) 29. Consider the following two equilibria and their equilibrium constants: Equilibrium constant 2SO2(g) + O2(g) 2SO3(g) K1 2SO3(g) 2SO2(g) + O2(g) K2 Which of the following expressions correctly relates K1 and K2? A. K2 = K12 B. K22 = K1 C. K2 = K1 D.

K2 =

1 K1


CHEMISTRY 7

Directions: Questions 30 to 31 refer to the following diagrams.

The above four diagrams represent a mixture of gases at different times at the same temperature. The equation of the reaction is shown below: A2(g) + B2(g)

2AB(g)

where Kc =

[AB(g)]eqm 2 [A 2 (g)]eqm [B2 (g)]eqm

30. Which of the above diagrams has the highest value of reaction quotient? 31. If diagram B represents the system which is already at equilibrium at that temperature, which of the above diagrams represents the equilibrium position when a positive catalyst is added? 32. Which of the following changes is correct when a positive catalyst is added to an equilibrium system with an endothermic forward reaction? A. More products are formed within the same period of time of reaction. B. The equilibrium position of the reaction shifts to the left. C. The equilibrium position of the reaction shifts to the right. D. No change in the concentrations of the reactants and products. 33. The rate of reaction of magnesium with acid is studied at 25°C. Which of the following cases will have the highest initial reaction rate? A. 0.5 g magnesium powder reacts with 100 cm3 of 1.0 mol dm–3 HCl. B. 0.5 g magnesium powder reacts with 50 cm3 of 2.0 mol dm–3 HCl. C. 0.5 g magnesium powder reacts with 100 cm3 of 1.0 mol dm–3 CH3COOH. D. 0.5 g magnesium powder reacts with 50 cm3 of 2.0 mol dm–3 CH3COOH. 34. Which of the following properties is/are common for iron and calcium? (1) Existence of variable oxidation states (2) Reaction with dilute hydrochloric acid to form hydrogen (3) Corrosion upon exposure to moist air A. (1) only B. (2) only C. (1) and (3) only D. (2) and (3) only


CHEMISTRY 8

Directions: Each question below (Questions 35 to 36) consists of two separate statements. Decide whether each of the two statements is true or false; if both are true, then decide whether or not the second statement is a correct explanation of the first statement. Then select one option from A to D according to the following table: A. B. C. D.

Both statements are true and the 2nd statement is a correct explanation of the 1st statement. Both statements are true and the 2nd statement is NOT a correct explanation of the 1st statement. The 1st statement is false but the 2nd statement is true. Both statements are false. 1st statement

2nd statement

35. One mole of methane occupies the same volume as one mole of carbon dioxide at the same temperature and pressure.

The molar volume of any gas is 24.0 dm3 mol–1 at room temperature and pressure.

36. The best method to purify ethanol contaminated with ethanoic acid is to mix the liquid with sodium hydroxide solution.

Ethanoic acid reacts with sodium hydroxide to form sodium ethanoate and water.

END OF PART II END OF SECTION A


CHEMISTRY 9

Section B PART I Answer ALL questions. Write your answers in the spaces provided. 1.

Consider the following situation and answer the questions that follow. Imagine that your elder sister, Angel, is a scientist. After 20 years of hard work, she finally confirmed the existence of a new element, with atomic number 119, following the last element (with atomic number 118) in the Periodic Table. This element was artificially made in the laboratory and finally approved to name after your elder sister. It is called ‘Angelium’. After seeking opinions, the chemical symbol of ‘Angelium’ was designated to be ‘Ae’.

(a) (i)

In which group and period of the Periodic Table should ‘Angelium’ be placed?

(ii) What is the name commonly given to the group of elements, in which ‘Angelium’ belongs to?

(b) The following three options of the suggested symbols of ‘Angelium’ were considered to be inappropriate. Give ONE mistake for each of the suggested symbols. Suggested Symbol Mistake Option 1 Ang Option 2 Ag Option 3 AE (c) (i)

Suggest ONE reason why the chemical properties of ‘Angelium’ are very similar to that of elements such as potassium and caesium.

(ii) Potassium can form potassium oxide (K2O) when exposed to air. Write the chemical equation for the reaction between ‘Angelium’ and oxygen to form ‘Angelium’ oxide.

(d) Draw an electron diagram, showing electrons in the outermost shell only, for the compound formed in (c)(ii).

(8 marks)


CHEMISTRY 10

Answers written in the margins will not be marked.


Your elder sister concluded that the chemical properties of ‘Angelium’ are very similar to elements such as potassium and caesium.

Aluminium chloride adopts different structures depending on the temperature and its state. In aqueous state, aluminium chloride is hydrated by the surrounding water molecules to form [Al(H2O)6]3+ ion and Cl– ion, in which six water molecules directly attach to the central aluminium ion. In liquid and gaseous states, aluminium chloride exists as dimers. At temperatures above 200°C, the dimers dissociate into a gaseous form, which is analogous to BF3 in terms of structure.


(a) (i)

Draw the three-dimensional structure of [Al(H2O)6]3+.

(ii) Give the name of the shape of this cation.

(iii) State the type of bond that exists between aluminium and oxygen in water.

(b) Draw the three-dimensional structure of gaseous aluminium chloride dimer. You should show clearly the type of bonds that exists between aluminium and chlorine.

(c) (i) Draw the structure of the gaseous form at temperatures above 200°C.

(ii) Give the name of the shape of this gaseous form and state its bond angles.

(7 marks)


CHEMISTRY 11


2.

3.

Explain the following phenomena.

(b) Explain why SbCl3 has a net dipole moment, whereas SbCl5 does not. Draw suitable diagrams to illustrate your answer.

(7 marks)


CHEMISTRY 12



(a) Explain why bromine can dissolve in 1,1,1-trichloroethane in terms of the specific types of intermolecular forces of attraction present.

4.

A type of portable fuel cell operates using a liquid fuel, such as petrol and methanol, in which chemical energy is converted into heat energy, and finally into electrical energy. Let us look at the working principle of a portable hair curler. Liquid fuel is put in a cartridge and the vaporized fuel is mixed with air and passed into a combustion chamber coated with platinum. When the fuel gas/air mixture is ignited, an exothermic reaction heats up the curler and will continue until the supply of fuel is turned off. (a) Write a chemical equation for the reaction that occurs during the operation of a portable hair curler, using methanol as liquid fuel.

(ii) Suggest ONE method to ignite the fuel gas/air mixture in the combustion chamber.

(c) Suggest TWO criteria for a portable energy supply.

(d) Justify whether petrol or methanol is more suitable to be used for fuel in a portable hair curler.

(6 marks)


CHEMISTRY 13



(b) (i) Suggest ONE function of platinum inside the combustion chamber.

5.

Hydrogen peroxide can act as a powerful oxidizing agent as well as a reducing agent under certain conditions. (a) Draw the three-dimensional structure of a hydrogen peroxide molecule.


In each case, (1) state whether H2O2 acts as an oxidizing agent or a reducing agent; and (2) state the change in oxidation number in oxygen. (i)

Fe2+(aq) reacts with H2O2(aq) to form Fe3+(aq)

(ii) MnO4–(aq) reacts with H2O2(aq) to form Mn2+(aq)

(7 marks)


CHEMISTRY 14


(b) Write the overall equations for the reactions below.

6.

The standard enthalpy change for the combustion of phenol, C6H5OH(l) is –3050 kJ mol–1. (a) Write an equation for the combustion of phenol.



(b) By drawing an enthalpy change cycle, calculate the standard enthalpy change of formation of phenol. Given that the standard enthalpy changes of formation of carbon dioxide and water are –394 kJ mol–1 and –286 kJ mol–1 respectively.

(5 marks)


CHEMISTRY 15

7.

Seawater is a mixture of a large amount of substances. It covers about 70% of the Earth’s surface. The salinity of seawater is ranging from 3.2% to 4.0%. On average, it is approximately 3.5%. It is equivalent to dissolving 35 g of salt in 1000 cm3 of water (roughly equivalent to 1000 g of water). The following table gives the percentage composition by mass of some elements in seawater. Name of elements W X Y Z Magnesium and other elements

Percentage composition by mass 86.0 10.7 1.9 1.0 0.4

It is known that W, X and Y are non-metals, while Z is a metal.

(b) Draw an electron diagram, showing electrons in the outermost shell only, for the compound formed between (i) W and X;

(ii) Y and Z.

(c) (i) Low salinity is found near polar regions, particularly during summer seasons. Explain briefly.

(ii) The Red Sea is located in the desert region. It shows the highest salinity (4.0%) of all the oceans. Suggest TWO reasons for this.

(7 marks)


CHEMISTRY 16



(a) Name the elements W and Y.

For question 8, candidates are required to give answers in paragraph form. For this question, 6 marks will be awarded for chemical knowledge and 3 marks for effective communication. 8.

Give detailed experimental procedures to show how you can prepare 200 cm3 of artificial salt solution of exactly 3.5% salinity. (It is equivalent to dissolving 35 g of table salt in 1000 cm3 of water.) You can only use the following reagents and apparatus: Table salt, distilled water Reagents Apparatus Electronic balance, 250 cm3 beaker, weighing bottle, 100 cm3 measuring cylinder, glass rod, spatula



(9 marks)


CHEMISTRY 17

END OF PART I


18

CHEMISTRY



PART II Answer ALL questions. Write your answers in the spaces provided. 9.

Transition metal ions are commonly used for catalysis. For example, the reaction between aqueous potassium sodium 2,3-dihydroxybutanedioate (C4H4O62–(aq)) and hydrogen peroxide solution is very slow at room temperature, even when heated. It can be speeded up by using cobalt(II) ions. The equation involved is shown below: C4H4O62–(aq) + 3H2O2(aq) → 2CO2(g) + 2HCO2–(aq) + 4H2O(l)

(a) Suggest how you can follow the progress of the reaction.

(b) (i)

Explain why the colour of the mixture turns from pink to green and then returns to pink as the reaction proceeds.

(ii) Suggest how you can keep the green colour for several minutes without returning to pink during the progress of the ‘traffic light reaction’.

(c) Explain why cobalt(II) ions can be used as a catalyst in this reaction.

(7 marks)


CHEMISTRY 19



The catalysed mixture appears pink initially due to the presence of cobalt(II) ions. During the reaction, the mixture turns green. When the reaction is complete, the mixture returns to pink. This explains why the reaction is sometimes called ‘traffic light reaction’.

10. The inter-conversion between the isomers of but-2-ene is represented by the equation below.

ISOMER A

ISOMER B

The value of the equilibrium constant, Kc, for this reaction is 3.2 at 25°C and 1.0 atm. (a) (i) Name the type of isomerism that exists between the two isomers.

(b) At equilibrium at 25°C and 1.0 atm, which isomer is present at a higher concentration? Justify your answer.

(c) If 1.50 mol dm–3 of pure isomer A was introduced into an evacuated container at 25°C and 1.0 atm, calculate the equilibrium concentration, in mol dm–3, of isomer B.

(d) Given that value of Kc for this reaction at 125°C is 1.3, predict whether the forward reaction is endothermic or exothermic. Justify your answer.

(8 marks)


CHEMISTRY 20



(ii) Give the systematic name of each isomer.

11. In each of the following substances, give an appropriate example from Period 3 of the Periodic Table and write appropriate equation(s) of a chemical reaction, if necessary, to show what is meant by (a) a basic oxide;



(b) an amphoteric oxide;

(c) an acidic oxide; and

(d) a neutral oxide.

(5 marks)


CHEMISTRY 21

12. Esters are compounds widely found in nature. They have pleasant odours. Food and beverage manufacturers often use them as additives to enhance flavour or odour. Although the fruity tastes and odours of esters are pleasant, they are seldom used in perfumes or scents that are applied to the body. The ingredients of more expensive perfumes are hydrocarbons (terpenes), ketones and ethers extracted from natural sources. The reason is that ester is not as stable upon sweating as the more expensive ingredients.

(a) Give the systematic name of ethyl butyrate.

(b) (i)

Name TWO organic compounds used for the formation of ethyl butyrate by esterification.

(ii) Give the reagent(s) and condition(s) that are necessary for the formation of ethyl butyrate during esterification.

(c) Explain why ester is unstable upon sweating. By using ethyl butyrate, write a chemical equation to illustrate your answer.

(d) Suggest ONE disadvantage of adding esters as additives in food.

(e) ‘A good-quality flavouring agent can be made from a single ester.’ Comment on this statement.

(8 marks) END OF PART II END OF SECTION B


CHEMISTRY 22



Ethyl butyrate is an ester with a smell like that of pineapple. The structure is shown below:


CHEMISTRY 23

HKDSE CHEMISTRY SECONDARY FIVE EXAMINATION PAPER (SET 1) SUBJECT: CHEMISTRY SUGGESTED ANSWERS for Section A 1. 11. 21. 31.

A D B B

2. 12. 22. 32.

A A A A

3. 13. 23. 33.

D B C B

4. 14. 24. 34.

A B C D

5. 15. 25. 35.

6. 16. 26. 36.

D B D A

B A C C

7. D 17. C 27. B

8. C 18. D 28. A

9. B 19. C 29. D

10. C 20. D 30. C

SUGGESTED ANSWERS for Section B 1.

(a) (i) Group I, Period 8 (ii) Alkali metals (b) Suggested symbol Option 1 Ang Option 2 Ag Option 3 AE

[1] [1] Mistake Three letters Same as existing symbol of silver Two capital letters

(c) (i) They have the same number of electrons in the outermost shell. (ii) 4Ae(s) + O2(g) → 2Ae2O(s) (d)

[3] [1] [1]

[1] 2.

(a) (i)

(ii) Octahedral (iii) Dative covalent bond

[1] [1] [1]

Correctly shows dative covalent bond

[1] [1]

(b)

HKDSE CHEMISTRY S5 Exam Paper (Set 1) Suggested Answers © Aristo Educational Press Ltd. 2011

CHEMISTRY A1

(c) (i)

(ii) Trigonal planar; 120° 3.

[1] [1]

(a) When bromine and 1,1,1-trichloroethane have not been mixed, van der Waals’ forces exist between bromine molecules and between 1,1,1-trichloroethane molecules. [2] When bromine and 1,1,1-trichloroethane are mixed, the amount of energy released from the formation of van der Waals’ forces between bromine molecules and 1,1,1-trichloroethane molecules is large enough to compensate for that required to break the van der Waals’ forces between 1,1,1-trichloroethane molecules. Hence, bromine can dissolve in 1,1,1-trichloroethane. [2] (b) SbCl3 has a trigonal pyramidal structure.

[1] SbCl5 has a trigonal bipyramidal structure.

[1] The dipole moments of three polar Sb–Cl bonds do not cancel out in SbCl3 and the five dipole moments cancel out each other in SbCl5. [1] 4.

(a) CH3OH(l) +

3 O2(g) → CO2(g) + 2H2O(l) 2

[1]

OR 2CH3OH(l) + 3O2(g) → 2CO2(g) + 4H2O(l) (b) (i) Catalyst; to increase the rate of combustion. [1] (ii) Any ONE: [1] - by creating sparks - by electrically heating the platinum (c) Any TWO: [2] Compact/lightweight/constant supply of electricity/long-lasting supply of electricity (d) Methanol is a more suitable fuel. Any ONE explanation: [1] because it burns more completely than petrol. / its combustion produces less black smoke and particulates. / it has a high efficiency of energy conversion.


CHEMISTRY A2

5.

(a) [1] 2Fe2+(aq) + H2O2(aq) + 2H+(aq) → 2Fe3+(aq) + 2H2O(l) [1] (1) Oxidizing agent [1] (2) Oxidation number of O decreases from –1 to –2. [1] – + 2+ (ii) 2MnO4 (aq) + 5H2O2(aq) + 6H (aq) → 2Mn (aq) + 8H2O(l) + 5O2(g)[1] (1) Reducing agent [1] (2) Oxidation number of O increases from –1 to 0. [1]

(b) (i)

6.

(a) C6H5OH(l) + 7O2(g) → 6CO2(g) + 3H2O(l) (b) ∆Hf 1 6C(s) + 3H2(g) + O2(g) → C6H5OH(l)

[1]

2

+6O2(g)

+O2(g)

+7O2(g)

6CO2(g) + 3H2O(l)

[2]

By Hess’s Law, 6∆Hf[CO2] + 3∆Hf[H2O] = ∆Hf + ∆Hcom 6(–394) + 3(–286) = ∆Hf + (–3050) ∆Hf = –172 kJ mol–1 7.

(a) W: oxygen (b) (i)

Y: chlorine

[1] [1] (only if both correct)

[1]

[1] (ii)

(c) (i)

When ice melts, the volume of water increases. Hence, the concentration of brine drops and the salinity drops. (ii) Desert region has very little rainfall. Desert region has a high rate of evaporation of water.

8.

[1] [1] [1] [1] [1]

Weigh out 7 g of table salt using an electronic balance. [1] Transfer the table salt to the weighing bottle using a spatula. [1] Pour the weighed table salt to a 250 cm3 beaker. [1] Measure 200 cm3 distilled water using a measuring cylinder. [1] First, pour 100 cm3 distilled water into the beaker. [1] Repeat with another 100 cm3 distilled water. (If only mentioned 200 cm3 water needed, without correct apparatus, award 1 mark only.) Stir the solution with a glass rod until ALL solid dissolves. [1] **3 marks for effective communication [3]


CHEMISTRY A3

9.

(a) Measure the volume of carbon dioxide gas produced [1] at regular time intervals (say 30-second interval) for 10 minutes. [1] Plot the graph of volume of carbon dioxide gas produced against time. [1] (b) (i) Pink cobalt(II) ions are first oxidized to green cobalt(III) ions. [1] Then cobalt(III) ions are reduced back to cobalt(II) ions. [1] (ii) To stabilize the reaction mixture by cooling it in an ice-water bath rapidly. [1] (c) Cobalt(II) ions can be oxidized in the first step and then reduced in the subsequent step. [1]

10. (a) (i) Geometrical isomerism (ii) A: cis-but-2-ene B: trans-but-2-ene (b) B is present at a higher concentration. Kc =

[ B]eqm [ A]eqm

and Kc > 1

[1] [1] [1] [1]

(c) Let the volume of the container be 1 dm3 and x be the change in concentration of isomer A. A B initial conc. 1.50 0 change –x +x eqm conc. 1.50 – x x Kc = 3.2 =

[ B]eqm [ A]eqm

[1]

x 1.50 − x

x = 1.14 ∴ the equilibrium concentration of isomer B is 1.14 mol dm–3. [1] (d) The reaction is exothermic. [1] At a higher temperature, Kc is smaller and less isomer B is present. Since the equilibrium position shifts to the left at a higher temperature, it indicates that the forward reaction is exothermic. [1] 11. (a) Na2O(s) + 2HCl(aq) → 2NaCl(aq) + H2O(l) (b) Al2O3(s) + 6H+(aq) → 2Al3+(aq) + 3H2O(l) Al2O3(s) + 2OH–(aq) + 3H2O(l) → 2[Al(OH)4]–(aq) (c) SO2(g) + 2NaOH(aq) → Na2SO3(aq) + H2O(l) (d) There is no neutral oxide in Period 3.

[1] [1] [1] [1] [1]

12. (a) Ethyl butanoate [1] (b) (i) Ethanol and butanoic acid [1] (ii) Concentrated sulphuric acid and heat under reflux [1] (c) On contact with sweat, esters undergo hydrolysis, giving organic acids. [1] These acids generally do not have a pleasant odour. [1] CH3CH2CH2COOCH2CH3 + H2O → CH3CH2CH2COOH + CH3CH2OH [1] (d) Esters would possibly attract fruit flies and insects. [1] (e) No. This is because the perception of flavour requires combined responses (bitter, sour, sweet and salty) from taste buds on the tongue. A complex mixture (in which a single ester predominates) is needed. [1]


CHEMISTRY A4

HKDSE Chem FX ExamS5 2011 Set1 Eng

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