16 FEB 1973
CITY HALL
育教僑華頁三第强八第 日三十月正年丑癸歴夏 WAH KIU YAT PO
橋
曰くく
T
1973英文中學會考試題預習專欄
點道英文書院主編
化學科(十七)
heat and electricity, brittle,
with a low melting point (113°C.
and low boiling point (444.6°0)
When heated
It melts at about 11500. an amber-coloured, mobile liquid,
At 16000., it becomes much darker in colour and very viseous,
iii) At about 230°C., the sulphur
gradually becomes more mobile again, and very dark reddish- brown in colour.
The sulphur boils at 44400.,. giving off light brown sul-
phur vapour.
-
With air or oxygen
Sulphur burns with a blue
lame, forming sulphur dioxide.
"3 Wath hydrogen
Sulphur vapour and hydrogen do combine readily if they are passed over a beated nickel cacabyst
H2
Ni
4. With carbon
When sulphur vapour is passed over very hot charcoal, the liquid carbon disulphide is formed.
123 +0
5. With metals
05.
Most metals combine directly
with sulphur,
\\S + Eg
/S Fe
Oxidising agent
HgS
FeS
Concentrated sulphuric acid and nitric acid slowly oxidise sulphur to sulphur dioxide,
50
20+ 350
S+ 4HWO
→ 21,0 + 3802
4NO
Ir the nitric acid is heated, the oxidation can go a stage fur ther to sulphuric aicd.
iruses.
S+ 2HNO
• H2SO4 + 2NO
Manufacture of sulphuric acid Manufacture of paper: Sulphur (18 used in the manufacture of
calcium bisulphite which is used to disintergrate wood fibre and to bleach paper pulp in the paper industry.
Vulcanisation of rubber: Sulphur to make the rubber strong, elastic, and resistant ito solvents as well as to heat
and cold.
Horticulture: Sulphur is used as a fungicide to prevent diseases in plants.
Minor uses
(1)
uses
Sulphur drugs for killing germs, e.g. sulphadiazin. in the manufacture of safety matches, e.g. Anti- mony sulphur,
111) in the gunpowder.
in the manufacture carbon disulphide.
Hydrogen sulphide (also called
sulphuratted hgdeogen).
by the action of
dilute acid on ferrous sulphide.
Preparation
FeS + 2HCL
or Fes + H 504
FeC1+ BSA
Fe3O
ismail
of cold taniity
21
報日僑罩
Ferrous sulphide is first placed in a flat-bottom flask, As the said drops through the
thistle funnel, effervescence
begins and the hydrogen sulphide. is collected over hot water or by downward displacement of air.
It can be purified by washing the gan with a little water and dried with phosphorous pentoxide.
If the impure gas 10 passed
through a suspension of magnesium oxide in water, the hydrogen sulphide only being absorbed to form magnesium hydrosulphide. When this is heated to 6000.... hydrogen sulphide is evolved and lean be collected as a pure gau
2H 5
Tests
1)
Mg (HS),
H_S blackers leau
acetate paper. 11) HS decolorices
potassium permangan -ate solution with sulphur deposited.
5H-S 3H SO
H2O +
2KMnO
KASO
Mn30
Properties:
It is a colourless, poisonous gas, smells of baŭ eggs, soluble in cold water, but not in war.
(1) Bums in air with blue flame.
HS+302
(2) As an acid.
-
2H0+ 250 (plentiful supply of air)
2H2O2S (limited supply
Dissolved in water, it turns Lumas colour. This scid is some- times called, hydrosulphuric acid It is a basic acid and can form. two series of salts, e.g
HS+ NaOH
NaHS H
H2S + 2NEOH • Na 5 • 2H_0.
Hydrogen sulphide reacts with salts of metals in solution
to form sulphides, many of which are in solubel and therefore pre cipitated,
Cuso
| Pb (NO 3 ) 2
HSO
2010
HAS
11)
As a reducing agent
reduces nitric acid to nitro- gen peroxide; 2HNOS
2H2O+S+2N02
reduces yellow ferric chlor- ide to green ferrous chloride
2Fe C1+2HC1+S. 27e013
H2S
iii) reduces conc. sulphuric acid;
3H S
→ 420 + 45
This reaction makes sulphuric acid an unsuitable drying agent for 1
H2S
reduces acidified potassium permanganate and potassium dichromate;
2KMnO
5H2+ 3H2S0 purple 2Mn50
+8HQ
colourless
yellow Cr(SO4)3
200 3H25-
green
7H 0+33)
sulphur dioxide to
2H + 502
20 + 381 reduces chlorine waveF hydrogen chloride.
H25
2H01
四期星
vii) Hydrogen sulphide in water
slowly turns cloudy on
2H S
2H 0 + 251
exposure to air.
Sulphides:
Preparation
By direct combination:
Fe+ S
Fes
By double ascomposition:
PbS + 2:NO.
Pu(NO3)2 + H2S
Cusu HAS
cus
iii) By heating a sulphate of the
metal with carbon.
Na SO +40
berties:
Na
400
All sulphides are insoluble except the sulphide of potassium, sodium, calciun, magnesium and aluminium. ii) Mest sulphides react with dilute hydrochloric acid, liberating hydrogen sulphids 111 Most sulphides from sulphur dioxide when heated in air. 1) The sulphides of the differ-
ent metals have different colour. e.g. Zine sulphide. (white); lead sulpaide (black) etc.
Exercise Fart I
1. When hydrogen sulphide is buru in excess of air the major produc of combustion are:
A.
• sulphur and water
B. sulphur trioxide and hydrogen C. sulphur dioxide and hydrogen
D. sulphur triode and water E. sulphur dioxide and watez
2. A liquid through which exceso hydrogen suphide has been passed reacts with barium chloride solut ion to form a white ppt. which is insoluble in dilute hydrochloric acid. The liquid was.
A. Sulphurous acid
B. potassium dichromate solution C. aqueous ferrous chloride
potassium permanganate Solution
E. doncentrated nitro acid
3. In the rea
tion
bath sulphur dioxide and hydrogen sulphide are oxidei ing agents
E
B. both dulphur dioxide and
hydrogen sulphide are reduo- ing agents
. sulphur dioxide is an Ox1019-
ing agent whilst hydrogen. sulphide is a reducing ge hydrogen sulphide is an oxidising agent whilst sul- phur dioxide is a reducing agent
The reaction is an example of precipitation
4. The tumiishing of silver in aır due to
A. moisture:
B. carbon dioxide C. sulphur dioxide. D. oxyger
E. hydrogen sulphide
5. To convert rhombic sulphur into. monoclinic sulphur the former is
A. dissolved in carbon disulphi filtered and the filtrate is evaporated.
B. heated to boiling then cool¤ã
suddenly.
0. heated to boiling then cooled
slowly.
D. heated untai 17 just melts
and then cooled.
exposed to air for a long time.
6. A solution of sulphur in carbon disulphide is quickly and safely evaporated to dryness by
. placing it in a shollow open
glass on top of a beaker of hot water in the fume cup- board.
neating it in a flask with a bunsen flame cupboard, heating it in an evaporating fish on a gauze ari triped over a bunsen flame in the flame cupboard.
日五十月二年三七九一届公年二十六國民華中
placing it in an evaporating
dish over a beaker of hot
water on the bench,
leaving it in an open dish
in the sunlight on
Ce bench.
7 The passage 01 nyarogen sulpmid produced the following changes
Decolarization of acidified potassium permanganent solution -
2. production of a black preci itate with lead nitrate. golution.
Tuming of blue litmus to red colour."
production of brown runes. when it is passed through nitric acid.:
Turning of orange acidified potassium dichormate solution to green,
P. A11
Q. None
R. 1, 4 and 5 only 5. 2, 3 and 4 only,
3 and 4 only
8. What is observed when hydrogen sulphide is passed through a solut -icn of zinc chloride, acidified with dilute hydrochloric acid?
P. A diy white precipitate is
... formed,
Q. A black precipitate is formed R. A gelatinous brown precipit-
ate is formed.
S. A yellow precipitate is fom-
ed.
T. No visible change cccurs.
9. When nyarogen sulphide is pass- ed into an acidified solutior of ferrous chloride, the solution changes colour and a precipitate is thrown down. The colour of final solution is
P.blue
Q. green
R. yellow
S. brown
T. colourless
10. Rhombic and monoclinic sulphur differ in that.
F. their atoms have different"
atomic numbers
Q. their atoms have different
numbers of neutrons
R. rhombic sulphur can be con-
verted to monoclinic sulphur easily, but the reverse change is difficult
rhombic sulphur dissolves ir carbon disulphide but mong- clinic does not.
they are different allotropes of the same element.
Part II
(a) Describe, with all pravulo al details, how you would obtai
Part II
(a) Describe, with all pract- ical details, how you would obtain hydrogen sulphide start- ing from sulphur, and ensuring that no hydrogen is produced at the same time.
(b) Draw a labelled diagram 01 a Kapp's apparatus for obtain- ing a constant supply of hydrogen sulphide, and explai its working.
(c) state one confirmatony) test for
to
the
gas,
(a) Give equations. and name the products formed when the gas reacts with:
1)
nitric acid ii) chlorine water i iii) sulphur dioxide iv) ferric chloride solution
(a) Describe briefly two ways by which sulphur is obtained as a by product in industry. (b) If hydrogen sulphide is prepared by using ferrous. sulphide, and if 2.2 gm. 0. this substance are used up. Calculate.
) the weight of nya rogen
sulphide produced;
11) the volume at N.T.E. or the gas evolved, if it has been collected at a pressure of 75 cm and a temperature. of 27°C, and has an abso lute density of 0.001365gm. per ce, under these oon- ditions.
(atomic weights: a = 32 Fe 56
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