B1 CCC HEEP WOH COLLEGE 2019 2020 FINAL EXAMINATION …

B1

2019 - 2020 / Form Five Chemistry / Section B / Final Examination / C.K.Lau

19-20

Final Exam

Chemistry

CCC HEEP WOH COLLEGE

2019 – 2020 FINAL EXAMINATION

F.5 Chemistry (Section B)

Date: 2-7-2020

Time Allowed: 8:30 a.m. – 11:00 a.m. (2½ hours)

Question-Answer Book

Name of Setter: Mr. C.K.Lau

Name: _________________________ ( )

Class: 5 ( )

Class Code: X / Y ____

Mark: ⎯⎯⎯

Instructions:

1. Read carefully the instructions on the Question-Answer Book and

insert the information required in the spaces provided.

2. When told to open this book, you should check that all the

questions are there. Look for the words “End of Paper” after the last

question.

3. Write your Name, Class and Class number in the spaces provided

on this cover.

4. This paper consists of TWO sections, Section A and Section B. Section

A carries 36 marks and Section B carries 84 marks.

5. Answer ALL questions in each section.

6. For Section A, mark all your answers on the Multiple Choice Answer

Sheet. You should mark only ONE answer for each question. If you

mark more than one answer, you will receive NO MARKS for that

question. No marks will be deducted for wrong answers.

7. For Section B, write your answers in the spaces provided in this

Question-Answer Book. Supplementary answer sheets will be

supplied on request.

84

B2


19-20

Final Exam

Chemistry

Answer ALL the following questions.

1. When ammonia dissolves in water, it ionizes to give ammonium ions and

hydroxide ions.

(a) Write an equation for the ionization of ammonia in water. [1]

(b) Ammonium ion is an example for illustrating the formation of dative

covalent bond.

(i) What is the meaning of the term ‘dative covalent bond’? [1]

(ii) Draw the electron diagram for ammonium ion, showing electrons in

the outermost shells only. [1]

(c) Ammonium salts react with alkalis to form ammonia. In an experiment, a

mixture of ammonium chloride solution and sodium hydroxide solution is

heated.

(i) Write a chemical equation for the reaction involved. [1]

(ii) Suggest a test to show that ammonia is an alkaline gas. [1]

B3


19-20

Final Exam

Chemistry

2. Answer the following questions:

(a) Explain how ammonia solution and sodium hydroxide solution of the same

concentration can be distinguished using aluminium nitrate solution. [2]

(b) How does tin-plating prevent iron from rusting? [1]

(c) Explain why mercury can conduct electricity in liquid state. [1]

B4


19-20

Final Exam

Chemistry

3. Iron is extracted from haematite in a blast furnace.

(a) What is raw material A? [1]

(b) Name the major component in haematite. [1]

(c) Write a chemical equation for the extraction of iron in the blast furnace.

[1]

(d) Is this method suitable to extract sodium from its ore? Explain your answer.

[1]

(e) Suggest one common use of iron. [1]

hot air

iron ore + coke + raw material A

hot air

hot waste gas hot waste gas

molten slag molten iron

B5


19-20

Final Exam

Chemistry

4. In traditional gold extraction process, gold-containing ores are ground into

smaller pieces before mixing with calcium cyanide solution. Air or pure oxygen

will then be bubbled into the mixture. ‘Gold cyanidation’ occurs accordingly:

4Au(s) + 8CN−(aq) + O2(g) + 2H2O(l) ⎯→ 4[Au(CN)2]−(aq) + 4OH−(aq)

Insoluble solids is then removed and the resultant solution is collected. Finally,

zinc powder is added to the resultant solution to recover gold.

(a) State the importance of grinding the ores into smaller pieces before ‘gold

cyanidation’. [1]

(b) The calcium cyanide solution used in ‘gold cyanidation’ is produced by

the reaction between hydrocyanic acid (HCN(aq)) and calcium

hydroxide solution.

(i) Draw the electron diagram for hydrogen cyanide molecule, showing

electrons in the outermost shells only. [1]

(ii) Write a chemical equation for the reaction between hydrocyanic acid

and calcium hydroxide solution. [1]

(c) Draw a labelled diagram to show how to remove the insoluble solids in

‘gold cyanidation’. [2]

(d) With reference to ‘gold cyanidation’, identify the species undergoing

oxidation and reduction respectively. Explain your answers in terms of

changes in oxidation numbers. [2]

(e) Explain why zinc can recover gold from the resultant solution. [1]

B6


19-20

Final Exam

Chemistry

5. The following set-up shows the electrolysis of 0.01 M copper(II) sulphate solution

with graphite electrodes (A and B) and copper electrodes (C and D) in two

electrolytic cells (P and Q) connected in series.

(a) What is the colour of copper(II) sulphate solution? [1]

(b) After passing electricity for some time, state and explain the change of

(i) the pH of copper(II) sulphate solution in cell P. [2]

(ii) the colour of copper(II) sulphate solution in cell Q. [2]

(c) After some time, the polarity of the batteries is reversed.

(i) What would be observed at graphite electrode B? [1]

(ii) Write a half equation for the reaction taking place at electrode C.

[1]

P Q

A B C D

dilute

CuSO4(aq)

B7


19-20

Final Exam

Chemistry

6. When lead(II) nitrate is heated strongly, lead(II) oxide, nitrogen dioxide and

oxygen are produced.

(a) Write a chemical equation for the thermal decomposition of lead(II) nitrate.

[1]

(b) State the changes in oxidation number of nitrogen and oxygen

respectively. [2]

(c) State and explain an observation in this experiment. [2]

(d) Explain why the experiment should be performed in a fume cupboard.

[1]

B8


19-20

Final Exam

Chemistry

7. Account for each of the following:

(a) HF has a higher boiling point than HCl. [2]

(b) Metals are malleable. [2]

(c) Carbon can form a large number of compounds. [2]

B9


19-20

Final Exam

Chemistry

8. Hydrogen peroxide is an oxidizing agent in acidic medium. It can be used as

an antiseptic.

(a) Draw the electron diagram for a hydrogen peroxide molecule, showing

electrons in the outermost shells only. [1]

(b) Hydrogen peroxide can oxidize iodide ions in acidic medium. State the

expected observable change and write an ionic equation for the reaction

involved. [2]

(c) With the aid of a chemical equation, suggest why the concentration of

hydrogen peroxide in a bottle of antiseptic decreases after prolonged

storage. [2]

B10


19-20

Final Exam

Chemistry

9. Sugar is composed of sucrose (C12H22O11). A can of 330 cm3 soft drink contains

11.0 g of sucrose per 100 cm3.

(a) Calculate the number of moles of sucrose in the can of soft drink. [2]

(Relative atomic masses: H = 1.0, C = 12.0, O = 16.0)

(b) Sucrose is a source of energy in the body. The following equation

summarizes the reaction involved when sucrose releases energy.

C12H22O11(s) + 12O2(g) ⎯→ 12CO2(g) + 11H2O(l)

The standard enthalpy changes of formation of some compounds are

given below.

Compound ΔHf (kJ mol−1)

C12H22O11(s) −2226

CO2(g) −393.5

H2O(l) −285.8

Calculate the standard enthalpy change for the above reaction. [2]

(c) Nutrient Reference Value (NRV) can be found in the nutrient labels. It is

based on a 2000-kcal diet and referring to the recommended intake levels of

various nutrients. Calculate the percentage of NRV for the can of soft drink.

(1 kcal = 4.2 kJ) [2]

B11


19-20

Final Exam

Chemistry

*10. You are provided with common laboratory apparatus, a magnesium ribbon

and dilute hydrochloric acid. Outline how you would perform an experiment to

determine the molar volume of hydrogen gas under the experimental

conditions.

[5]

11. Outline the synthetic route, with no more than three steps, to accomplish the

following conversion. For each step, give the reagent(s), reaction conditions

(as appropriate) and structure of the organic product. [3]

B12


19-20

Final Exam

Chemistry

*12. Aluminium, silicon and phosphorus are three consecutive elements in Period 3

of the Periodic Table. With reference to the bonding and structure of the three

elements, explain the difference in electrical conductivities between the three

elements. [5]

13. The structural formula of 2-chlorobutane is shown below:

(a) 2-chlorobutane exists in two isomeric compounds.

(i) Draw the three-dimensional structures for the two compounds. [1]

(ii) State one difference in physical property of the two compounds. [1]

(b) Outline a synthetic route, with no more than three steps, to accomplish the

conversion of butanal to 2-chlorobutane. For each step, give the

reagent(s), reaction conditions (as appropriate) and structure of the

intermediate. [3]

butanal

2-chlorobutane

B13


19-20

Final Exam

Chemistry

14. When pentan-3-ol is heated with concentrated sulphuric acid, two isomeric

compounds form.

(a) Name the type of reaction involved. [1]

(b) Write the structural formulae and names of the two isomeric compounds.

[2]

(c) Do the two isomeric compounds have similar chemical properties? Explain

briefly. [1]

(d) Suggest another reagent that can be used to replace concentrated

sulphuric acid in the above reaction. [1]

B14


19-20

Final Exam

Chemistry

15. Compound K contains carbon, hydrogen and oxygen only. It contains 66.7%

carbon, 11.1% hydrogen and 22.2% oxygen. The relative molecular mass of K is

72.0.

(a) Determine the molecular formula of K. [3]

(Relative atomic masses: H = 1.0, C = 12.0, O = 16.0)

(b) Given that K is a ketone, draw the skeletal formula of K. [1]

(c) When K is mixed with lithium aluminium hydride in dry ether and then the

reaction mixture is treated with dilute hydrochloric acid, alcohol L is

produced.

(i) Name the type of reaction involved. [1]

(ii) Suggest another reagent that can be used to convert K to L. [1]

B15


19-20

Final Exam

Chemistry

16. Two different samples of magnesium carbonates (A and B), each weighed 1.0

g, were allowed to react with 25.0 cm3 of 1.0 M hydrochloric acid under room

conditions. The volumes of carbon dioxide evolved with time are shown in the

graph below:

(a) Write a chemical equation for the reaction between magnesium

carbonate and hydrochloric acid. [1]

(b) For sample A, calculate the average rate of the formation of carbon

dioxide for the time interval from the 0th to the 40th second. [2]

End of Paper

time (s)

vo

lum

e o

f c

arb

on

dio

xid

e (

cm

3)

sample A

sample B

B1 CCC HEEP WOH COLLEGE 2019 2020 FINAL EXAMINATION …

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