WAH KIU YAT PAKA
真四第張五第日八初月二十年子壬歷夏
Sn
no acti
1913英文中學會考試題預習專欄
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Chemistry
For Last week
Water and Hydrogen
Water is a simple
of.
hydrogen and is. produc de ther.
with other products and energy. when organic substances are" bu rri ed in air or oxygen. e.g
Hydro carbon:
CxHy + (x++)0,→→→ F2O+X002+Heat
Ethylene:
C2H 302
Ethyl alcohol,
200 +Hea
CHOH 30
3H2O+ 200 Heat
Synthesis of water:
(1) Water is formed by burning dry hydrogen in air.
Hydrogen gas, dried by anhyd- rous calcium chloride, is made. to pass through a jet and allowed to burn in air and its flame is dir ected against a cooled surface. The liquid formed is tested by anhydrous copper sulphate..
2H
2H 0
(2) Water 18 formed by reduction
of copper oxide or lead oxide with hydrogen or coal was.
Freezing
Copper or head oxide is firs placed in a combustion tube and strongly heated. Hydrogen gas is. passed through and the vapour 190 condensed by a freezing mixture in a U-tube and tested by anhydr- ous copper sulphate.
CuO + H2
Cu
H2O
Action or metals on water:
Action of water on petals as Indiented by the post 1018 of the
lifferent metals in the Electro- Chemical series.
Metal on cold on steam
·Products formed:
water violently explosive KOH:
-1y:
-1y
violently explosive NaOH H
K
Na
Ca
quietly
Me
violently Ca(OH)
no action vigorous.
but slowly
with boi
Boiling water: Ng(OH)2
報日僑華
四期星
日一十月一年三七九一曆公年二十六國民華中: 育教僑華
great Suo H
difficulty
even with super-heat -ed steain
no action almost no.
action even with super-heat -ed steam
Metals below hydrogen cannot by 211 means decompose steam or water Hygroscopic substance: absorbs water from the atmosphere, e Jalcium oxide.
Deliquescent substance: absorbs 30 much water from the atmosphere that it froms a solution. Examples Calcium chloride, sodium hydroxide
fflorescent substance: hydrated
salt that loses water of crystall- Ization to the atmosphere. Exampl sodium carbonate, sodium sulphate Drying agents: used to dry gases, liquids or solids. Examples: Calcium chloride, concentrated sulphuric acid, phosphorus pent- oxide, sili ea gel.
Hydrogen:
1) preparation
a. Dilute Acids on granulated Zinc
Dilute sulphuric acid or hydro chloric acids will giv ve hydrogen when acted upon by Zinc. Zu + 2HC17 Zucl
H2SO
Zuso
All metals above hydrogen in the electro chemical series theo- retically react with dilute, non- oxidising acids to produce hydro- gen. But lead and aluminium are unsuitable for this preparation as they react too slowly. Sodium, potassium and calcium would give explosively violent reactions.
Hydrogen can be maus
From hot and cold.
strontium ang mamam réactiv cold
Jiperinne nyi
Water,
:(not)
NACH
Mg(OH
By the action of metal steam. Many metals such us Magn
Zinc, Iron and us renet with stea am liberating nya mgen.
4H50
M2O
By electrolysis of water. Hydrogen can be produced by pass ing an electric current throug water containing a little pr -ic acid. Hydrogen will be lin ated at the cathode and oxygen at the anode in the ratio of c. Hydrogen can be prepareU alkalis
Heat zinc or aluminiu
or potass
a solution of soda um
hydroxide; hydrogen 18 given off and a solution of sodium or potassium zincate or aluma na tes formed
Zu 2NaOH
(3| Hydrogen is neutr
and other indicator (4) with chlorine,
(5) If hydrogen is mobled unrou gh melted sulphur, nyorogen sul
phide is formed in small meld
H
Hydrogen
Cuo
*PbO
volume
agent
僑榮
contains many hydroxyl 2ons
has a miximum density at 4°C.
E. has many hydroxyl ions as well
as hydrogen ions.
6. Water at room temperature dões
1ot react with
P. potassium
Q. sodium
R. calciu
S. mangnesium
Coal gas cur
Uses of hydrogen:
(0) As, a fiel tains 5% by volume of hydrogeri
Water gas contains 45% bv
hydrogen. (2) As a reducing agent. (3) Making ammonia- In Habei process hydrogen and nitrogen are made to combine at very hign: pre- ssures in the presence of a cat- alyst to give ammonia.
N + 3H
(4) Harding or 011-
2NH
used in the manufacture of murĖS -ine by reaction with most natu oils in the presence of a heate nicked cotalyst.
(5) Marking petrol from coại. (6) Blowpipea-
It is use
the oxy-hydrogen blowpipe for Welding metals.
7) Balloons----- Owing to ite lightness, hydrogen is used in balloons and airships.
Rusting of iron:
When iron is left in damp air for some time it becomes cove -ed with reddishbrown rust, The rust forms only on the outside o the metal. Rust as soft and JL readily drop off, and then the metal below starts to rust.TIT. iron is left in air along enougn, it completely changes to iron rust.
Iron oxygen water->Iron
Therefore, that, the rusting iron needs both air and water. together.
Methods of prevention;
oil or grease is put on the metal to stop it rusting.
2. paint or tar.
3. A layer of other metal is put on the iron, e.g. tin-plate
4. Enamal is very hard and does not let air or water pass through it to the iron.
5. Stainless steel. It is iron that contains carbon, chromi tam nickel and other elements. It doc not rust.
Exercise
Part I:
1. Even on heating, hydrogeu can- not reduce
A. Zing oxide
B. Copper oxide
C. Ferric oxide
D. Mercuric oxide
E. Silver oxide.
2. Which of the following metals can displace hydrogen readily, from cold water?
Magnesium
3. Calcium
sodium
and
and
D.
2 and
E.
and:
iron copper
Which of the following efflor esces on exposure to air.
T. Aluminium-
7. When zine is dissolved in dilut sulphuric acid, hydrogen is given off. But if it is dissolved in nitric acid; oxides of nitrogen are obtained becaused
P. Zinc is higher in the electro
-chemical series than hydro- gen.
Q. nitric acid is a Week 0x1d18- ing agent than sulphuric acid nitric acid gives more hydro- gen ions than sulphuric acid nitric acid is a stronger re- ducing agent than sulphuric acid
nitric acid is a stronger oxidising agent than sulphuri acid
3. The principal uses of hydrogen are the
1. Synthesis of ammonia
2. Manufacture of hydrochloric
acid
hardening of vegetable and aimual oils
production of water gas production of producer
P. 1 and 3 only
Q. 1,4 and 5 only
R. 2, 3 and 4 only S. 3, 4 and 5 only
All
The fron rusts of prolonged xposure of a clean iron surface)
ary al
humid air pure water rain water:
dissolved substance
2 only
2 and 3 only
R. 1 and 3 only S. 2 and 4 only 1. All
10. Anhydrous calcium chloride t use in a dessicator because they
P. are very deliquescent
Q. are very efflorescent
R. are very hygroscopic
S. do not react with any gases. T. form hydrates
Hygroscopic means that
it absorbs water vapour from the atmosphere until za dis- solves,
AN
it absorbs water vapour from the atmosphere but will not. dissolve.
at reacts with water vapour from the 90 25 vine off whi fumes.
It gives up water vapour to, the air.
it absorbs the elements or water. from the organic com“, pounds to form water. Whaen of the following fflorescent substance A. Washing soda
B. common salt
C. caustic soda
D. quick Lane
E.
sodium thiosulphat
3. Rust 15
A. ferrous oxide
B.
ferrous carbonate
'an
ing water
A1
-game as
Mg
game as Mg
no action norme
2.
Steam: Mgo, H2
Boiling water: A1(OH).
Steam:
H2
Zuo,
no action reversible Fe
reaction with super -heated steam.
ZKUN
2A1+ 2NaOH+ 2H
ZAL + 2KOH
Method of resting nyaroxen
Cuso
B. Cu(NO
С. Кон
MATO
ZKA10
pplied
A mixture of hydrogen und 4) explotes when a flumes So, hydrogen can be detecter of burning with a little "pop":"unive quite from air.
Properties:
(1) Colourless, odourless almost insoluble in water, lightest substance known,
(2) Burns quickly in air or oxygen, with non- luminous, very hot, flame to form water
2×2.
28,0)
D. Zu (NO
NaCl
In the electrolysis or acidu lated water using platinum elect- rodes, the ratio of hydrogen to oxygen liberated by volume is.
A 1:2
B. 2:1
C. 1:8
D. 8:1
E. 1:16
5. Pure water nas Low electrical conductivity because
A. contains few hydroxy ions
a. contains few hydrogen ions
ferric hydroxide
D. ferric oxide
ferric carbonate
14. The electrolysis or 18 gm. acidulated water, will yield
A. 16 gm of oxygen and 2 gm of
hydrogen
B. 12 gm of oxygen and
hydrogen
C. 9 gm of oxygen and
hydrogen
6 gm of oxygen aru hydrogen
B. 2 gm of oxygen and
hydroger
Section 11
of
Describe how you would show that when hydrogen burns in air a liquid is produced which 18 water Your diagram must show the hydro- gen is prepared.
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