1989-12-23 — Page 28

波

日六廿月一十年已己曆夏

報日僑華

六期星 日三廿月二十(九八九一)年八十七國民華中( 28 )

Sulphur reactive.

is

3. Chemical Properties of Sulphur

chemically

5.4 The sulphite ion ($0.2") has

a

quite

3.1 Sulphur burns in air with a blue

oxidized to the

reducing properties because it is

Dn reducing: an electron donor. other substances, it is

sulphate

itselfi ion:

1990 中學會考預習專欄

明德出版社

flame,

giving

oxide(502)

and

oxide(50).

Sulphur (IV) sulphur(VI)

(504

1,2~).

MILL & DALE PRESS

50,

2(aq) + (0)-50

5+02

25 + 302 2503

3.2 Sulphur can combines directly with most metals and many non-metals to form the sulphides. Heating is required.

OIN. increases

(+4)

(+6)

allotropic forms.

Solid Sulphur

Crystalline

Amorphous

(4) 5(0) +

sulphran

J.

sulphur

fe.g. plastic

3.3 Sulphur

Rhombic Monoclinic

sulphur,

sulphur sulphur

powdered

(-sulphur)(-sulphur)

sulphur)

H2504 and conc. HNO3,

1.3.0ifferences between rhombic

and

is oxidized

oxidising agents such

لانا

5 + 2H2S043502 + 2H20

monoclinic sulphur:

1.1 Allotropes of an element are tne

forms of different crystal

the elements, i.e., the different ways

its constituent particles being Tarranged.

1.2 Solid sulphur exists

several

Copper (1) sulphide N.B. Usually the sulphides with the metals in the lowest oxidation

are obtained, e.y. (Cu*)¿§2ˆ‚

etc.

2.9. {3} H2{g} + S{0} ——— H2 Sig}

Chemistry (12)

R. Chu

Unit 7: Revision notes on Sulphur and

its compounds

0.9. (1) Fe + S FeS

iron(II) sulphide

(1)

Reagents 10,/AIF

with

2-

2-

1. Sulphur

(2) ZCu + S Cu2S

250

(aq)40, (g) -

· 250,

เล

7.3 Soiling

sulphur, Sodium sulphite forms sodium thiosulphate {"hypo").

its formation.

(c) What is Y?

its formation.

(2)

+ S

Na25203

ovolved

2-

ZHNO

strong

as conc.

(4)

0.N. increases

Rrobato sulphur Monocitald sulphur

(+4)

(5)

Acidified orange to green

Colour

|Bright yellow

Pale-yellow

Structure

3-malecules

S-molecules Sal

(5c) closely

backed

less closely packed

5+

·H2SO4 + 6ND2 + 2H2Q

(6)

2-

Iront Yellow to pale-green fsolution

30- +ZFe +8 504

Dansity Crystal shape

Higher

12:06 ge octahedral

Lower (1198 gem Needle-shoped

O.. increases

}

+2H

(+6)

[}}

Lead(IV) joxide

Black solid to White soild

30

P650

Examples

2-1ac)

Observations and Equations

Sulphate ions formed.

Conc. HNO, Reddish-brown yas (NO2); heat

(3)

Ha! agens

salution

2-

+heat greanish-yellow to colourless

2-

CI,+40-50

22

2 +2 +201

0: orange-yellow to

colour less

Sulphites and hydrogen sulphites

Sulphu-

Dioxida

Oxygen

and

to

hydrogen give

2-

Purifier

Purifier

.1 Soluble sulphites

sulphites dissociate

So,(aq) when dissolved in water,

so, they give similar reactions as aqueous 50, solution.

7.2 Dilute strong acids liberate S02

from metal sulphites and hydrogen- sulphites. Heating is sometimes required.

50,2 ̄(s)+24(aq)

Convert packard with

a catalyst at 450°C

Concentrated sulphuric acid

Absorption Tower

water

- H2(#)+502 (q) || (a) Suggest a method by which sulphur

dioxide is readily obtained.

·H2{2}+502(9) (b) what is X? Write an equation of

7.4 White precipitate is obtained on adding barium chloride or barium nitrate solution to some aqueous

2-

50,2. The precipitate is dissolved HNO to it."

on adding dilute HC1 or

2+

2-

1+50,

2-

+8+1,050 +2H +2Er

10: Fight-brown fo

colcur less

22

Acided Purple to calourless KMnO

2-

+2K +21

3a503(s)+2H*(aa)

Ba503(s)

Ba2+(aq)+H20{e}+5Q2(9)

7.5 Test for sulphite/hydrogen sulphite If 90 is detelted on adding a

dilute strong acid (e.g. HCL, HNO3)

hydrogen

to a solio, then the solid is a metal sulphite or sulphite.

Write an equation of

(d) Name a suitable catalyst to be pub

in the converter.

(e) Why are sulphur dioxide and oxygen to be purified before they are passed into the converter?

(f) Why is concentrated sulphuric acid,

out Fot

added water,

to the

absorption tower?

Solution to 0.7.1

(a) X is sulphur dioxide.

Na 50

=2HC1 NaCl + H2O + SO2

(b) The bromine water turns from yellow

to colourless.

+ 2HBr

50,

21120+ Brz

-H2504

(c) The set-up is shown as below.

dliute tydrochloric

acid

test tuba

sod Iuin

sulphite

Bromine

water

Hust

crystals

The mal Istability

Preparation By evaporation

X.P.

Stabia beny

96°C

Stable above 95°C

113°C

119°C

lot sulphur

By slow cooling of walten sulphur.

solution in

96 C

1.4 Rhombic

Monoclinic sulphur

95°C

Sulphur

Thus,

is known transition temperature.

2. Effect of heat on sulphur

2.1 Observation

as the

Lenon-yellow 113°C, solid

Metts

Maalie, clear

amber liguld 114°C

to

Mobite.

dark-red

營爍

Liquid

閃燦生輝誌永恆

贊誌

TAK SEK 21 2

1:91°C to

44890

1190°C viscous, deep- red liquid

sudden

bolis

at 445°C

cool Ing

Brow

Plastic

gapour,

挐恆

延

2.2 Explanation

*

O C

·00

一日千里的香港

張婉嫺(維多利亞工業中學 )

|了-一代而有著不同的表港人對祖國忘情,只

打算,也是人之常情,是在這個大時代的洪流

molecules

closely packed

in solid s

wwww

wwwwww

Sulphur

113°CAA ats molecules

separated on meiting

1910

444°C

long chains broken to small chains

which align

regulady

poils at +45°C

sa. Chains broken up

to give S molecules

in vapour

1114°C to

190°C

molecules

broken up to give chains, chains strangled and joined up together

1990 中學會考預習專欄

明德出版社

MILL & DALE PRESS

4. Uses of sulphur

(1) In manufacture

Contact Process.

(2) In

making

of H2SO4 by

calcium hydrogensulphite Ca(HS03)2 for bleaching wood industry.

paper

(3) Im vulcanizatjag be rubber

(making it hard and

(4) In making matches."fireworks.

guruwderão.

(5) Assiede insecticide and

soil conditioners.

(6) in sulpur ointments. tablets

and drugs.

(7) In making "hypa" Isodium thiosulphate, Na3203 520).

5. Chemical Properties of 502.

(5.1 Dry 50 is rather inert.

SO2 becomes very reactive in the bresence of water.

5.2 when dissolved in water 50 reacts

can bleach straw paper, reduction and silk by

5.5 Aqueous 50

wool reaction. Thus, its bleachfect is only

porary because thewatour wil be recoveredug to oxidation

H250+(dye - 0)

colourless

5.6 50 can also act as an oxidising agent when it reacts with a strong reducing agent, e.g. burning Mg, hydrogen sulphide H2S, etc.

e.g. (1) Burning Mg continues

10

burn in SC to give white clouds of magnessium oxide and yellow deposits of sulphur.

+ 2Mg →→→ 2Mg0 + `s

S02

0.N. decreases

(0)

(+4)

(2) Yellow deposits of sulphur are seen when 50 reacts

with HS in the presence

براج

with water to form the Sulphurous acid (H2503) which then fomizes give hydronium ions (

to

a water.

trace amount of

502

+

245-2420 + 35

hydrogensulphite ions (HS0," the sulphite ions (5032").

502{9}+H20(e)~K2502(aq)➡x*(aq)

•luso_*(eq)=2H*(aq)-50 0,2-(aq)

3

All these changes are reversible. Thus, aqueous $0 solution consists

2-

of Hot, H50 and 50 ions.

5.3 Sulpherous acid is a weak dibasic acid. it forms two series of salts 2-

by neutralization: sulphites 503 (normal salt) and nydrogen- Sulphites, H50, (acid salt), e.g. Na2503, kHS03, etc.

Computer (12)

K. Choy

Program debugging is an inevitable event after program coding. There are 3 main types of error:

(1) Syntax error:

It is the programming error in which the program statement is not written and presented exactly as the syntax (rule) of the language. It is the easy part of the correction. Most HKCLE questions ask questions in this style.

(2) Execution error:

6. Uses of SO, (and sulphites): (1) As bleaching agent. [2) As food preservatives. (3) As disinfectant. (4) In manufacture

acid.

of sulphuric

502

H20 503-

H2S04

(5) In

2t catalyst

purifying the fractions of petroleum.

light

Question 7.1

A gas X is evolved on warming socium sulpaite crystals with ат excess of dilute hydrochloric acid. The gas X is 2 cm3 of bromine then bubbled into water,

the gas X.

an equation of its formation.

t would happen to the bromine Water?

Write an

observed.

(c) Draw a de

would use

experiment.

the changes

the apparatus you carry out the above

Gas X can also be obed herting copper turnings with some suloburic acid.

(d) Write an equation of the reaction. (e) What property of concentrated sulphuric acid is indicated by the above reaction?

(F) Would gas X be obtained by sing dilute sulphuric acid and dopper? Explain briefly.

A student passed an excess

into 5 cm3 of 1 M sodium hydroxide

(d) Cu 2250 CuSO4 2H20 + 502 (e) The oxidizing power of conc. H2504-

(f) No. It is because dil H250, is not

an oxidising agent.

(g) Sodium hydrogen sulphite (NaHS03).

་ །

502 Näoh

NAH503

(h) The yellow solid is sulphur.

white solid is magnesium oxide.

MC SO.

2Mg0 + 5

The

(i) Gas

not X (SC2) does support-- combustion, as a candle flame is extinguished in it. However, the energy liberated by the burning magnesium S great enough to decompose gas X (502) to sulphur. and oxygen, so, it can continue to wurn in the Oxygen to form magnesium oxide.

(1) The set up is:

X

solution.

resulting

He then solution to

the

-deflagrating

and

spoon

gas X

obtained Some

white Bad as

the

residue.

gas jor

burning magnesium

ribbon

(g) Name the white" obtained on evaporationWritevan ecuation of

its format

When Caning, hestum ribbon was put into

gas X, the magnesium continued to burn with a spluttering Fame, giving a white and a yellow solid. However, if a burning candle was put into the gas X, the candle Flame was at once extinguished,

(h) what would be obtained from the

burning magnesium in gas X? Write an equation of the reaction,

the !(i) Explain

observation in the above experiment.

(1) Draw a diagram of the apparatus you would use in carrying out the above experiment.

Question 7.2

The manufacture of sulphuric acid by the Contact Process is represented by the schematic diagram below.

score more than 15 out of 25 marks. It is good that you practise 160 well for such kind of question. But on hand experience is 170 important.

Solution to 0.7.2

(a) Sg is obtained by burning sulphur nair or by roasting iron pyrite (FES)

in air.

(b) X is sulphur trioxide.

2502(g) + O2(g) → 250,(9)

(c) Y is alouc.

H2SO4(2) + 503(9)

~H 2 S2 Cz { P }

(d) Platinum or Vanadium(V) oxide.

(e) The impurities in 02 or 502 would

poison the catalyst.

(f)

503

Forms misty acid fumes coming into contact with water, whereas it dissolves readily and smoothly in conc. H2504-

PRINT "THE FIRST N TERMS OF PRINT "THE FIBONACCI SEQUENCE: “

100

REM PRINT SEQUENCE

190

200

FOR 1 TO N PRINT A

END

For such kind of questions, you only have to give the line 210 number and the corrections required. Remember not to rewrite the whole program and not to change the style of the program in order to score high mark.

Exercise

Fibonacci sequence can be generated by the addition of 2 previous consecutive terms as following.

A1

A

=.0

=1

Аз

+ A12 01 1

A1 = Ar-2 + Ap~1

where 3, 4, 5, .....

It is also the programming error that the program cannot be execute when the BASIC interpretor detects such an error. Most Connon errors include divide a number by zero and not enough A student writes the following program to find the first few terms dimension for arrays. Therefore we have to use extreme data for of the Fibonacci sequence. Study the program carefully.

program testing,

State what corrections should be made so that the program will produce the output below on the VDU. In the output, -7 and 5 are jentered through the keyboard by the user, All other items are from

the program.

[A PROGRAM TO GENERATE TERMS OF FIBONACCI SEQUENCE

HOW MANY TERMS? -7

THE NUMBER OF TERMS MUST BE AN INTEGER GREATER THAN ZERO! HOW MANY TERMS? 5

THE FIRST 5 TERMS OF THE F130NACCI SEQUENCE: 10

1

Answer:

1

Line number

2

3

Correction

10

Change to 10 PRINT "A PROGRAM TO GENERATE TERMS OF

10 WRITE "A PROGRAM TO GENERATE TERMS OF

20

Change to 20 PRINT "FIBONACCI SEQUENCE"

20

FIBONACCI SEQUENCE"

30 DIM A(N)

50

Change to 50 PRINT "HOW MANY TERMS?";

40

PRINT

70

50

PRINT HOW MANY TERMS?

Change to 70 TF NO AND N = INT(N) THEN 110

60

INPUT N

90

Change to $0 GOTO 50

70

IF NO AND N INT(N) THEN 50

80

PRINT "THE NUMBER OF TERMS MUST BE AN INTEGER GREATER THAN

170

Change to 120 A(2) = 1

ZERO!"

130

Change to 130 FOR 1 - 3 TO N STEP 1

90

RETURN 50

150

REMARK GENERATION OF TERMS

Change to 150 NEXT 1

110 A(1) = 0

155

Insert line 155 PRINT

160

Change to 160 PRINT "THE FIRST N TERMS OF";

A(1) = A{I - 2) + A(L - 1) NEXT J

205

Insert line 205 NEXT I

(3) Logical error:

It is the most common error found in the algorithm of the problem. The program may or may not run. If it runs, the answer given by the program must be incorrect. Therefore testing the program must involve calculating the answer manually. Hore that one set of data are suggested so as to make Sure that no error occur for a special set of data. It is the most difficult when doing debugging. A careful and accurate 100 flowchart may be useful to avoid this type of error.

Program Correction is a compulsory question in the HKCEE.

120 A(2) = 2 130 FOR I=1 TO N STEP 2 Most 140

students can answer this question satisfactorily. Most candidates 150