真四第張四第
報日僑華
六期星
日十月一十年三七九一层公年二十六國民菲中養育教
日六十月十年丑癸靨夏
WAH KIU YAT PO
基士及校
HERE
****
*
CHORI
CHRZU
EXTE
BERKE
KEN
**SH
與大校長
博士
瑞敏博士奥欺
學校長李卓
「香港中文大
雅斯敦授
(57
二攝光者報
眞寫禮典位學授頒屆第學大港香
燕副午海大分 午 位六五大
1974中學會考試題預習專欄
1 MM
化學科(課程乙) (-)
CHEMISTRY (T),
Preface
This revision notes and
exercises is intended for use in the preparation of student for the H.K.C.E. Examinations in chen- istry. The present volume contains my selection of the important items from the H.K.C.E.E. syllabus. With this object in view, there are discussions of number of physical,
inorganic and organic chemistry.
The exercises given at the end of each topic contains many multiple choice items and convention al questions and a suggested ancrer will also be river on next volume before the other tonic.
A suplement to this volume contains 3 test baners each of which consists of a lot of M.C.q; and 5 conventional questions for the... candidates to revise. The treatment here is therefore not intended to be exhaustive, but it is honed that. this will be particularly useful students in their final year in secondary school course..
1. Introductory investigations
nfrases
A. Collection & Handling ~
(1) Gases prepared without heat
and collected over wateri
H2, CO2, H2S, NO, CO)
Trepared with heat collected over water.
(2) N2 N2O, CH
(3) Gases prepared with heat and usually collected by downward delivery. (1.e., HC1, SO,, Cl2).
(4) Ammonia has a special apparatus
for its preparation because it is
the only common gas which is usual. ly prepared dry and collected upward delivery.
Quicklime
or Soda-line
The use & construction of the Bursen
The Bunsen : flame:
Barrel or chimney
Metal ring
Air from outside
(1) Non-luminous flame(air-holes
open)
When the holes are open, air enters the tube and mixes with the coal gas. The ras therefore burns more quickly and completely We can distinguish three distinct
zones:
An inner zone of cool, unburni Pas
A green or blue middle zone. The coal gas burns in this zone but not completely, because there is not enough air.
2H202
CH
2CH
302
2420 2H2O + CO2 2.CO
A male blue outer zone. In this zone the burning of the
gas becomes complete.
coal
200
+
02
2002
(2) Lumincs flame (Air holes
closed).
When the holes are closed and no air enters the tube, the flame is large and bright, The four zones of the flame as follows:
A dark inner zone of cool unburnt gas.
b. A luminous yellow zone. The
coal gas burns in this zone but not completely as there is not enough air. Tiny particles of solid carbon form.
CH+02
220
C
c. A thin outer zone. In this
zone the coal gas burns completely.
d. A blue zone at the bottom of the flame. This part receives olenty of air because the air near the flame rises rapidly.
Thin outer
zone Luminous
& yellow Unburnt
дав
Concentrated Sulphuric acid.
Air
Blue
rises
Pale-blue or purple Green for blue Unburnt
Fas
C. Methods of burification & Separa-
tion.
(1) Distillation is the process of
biling a liquid to form vanour and then cooling the vapour to obtain the liquid, which used to recover the solvent from solution.
(2) Fractional distllat on in th
11 process of separatin two.
by distillation, the disc being collected in:
boiling at differeperatures
3) Crystallisation is the process of forming crystals by lowering the temperature of a saturated solution, which used to recover the solute from a solution. (4) Fractional crystallisation is
the process of sonorating two or more solutes by crystallisation. making use of their different. solubilities in the same solvent. (5) Filtration is a process of
separating a linuid and a solid in sus ensian. The substance nemairing on the filteraner is called the reside and theliquid passing through the filter namer is called the filtrate.
Solution
A solution is a homogeneous molecular mixture of two or more substances, in which one substance is in noticeably great
eter proportion than the other
If we have a solution consisting of a mixture of two substances, the substance in greater proportion is called the solvent, while the other, is called the solute.
Following are some common.
solvents:
water
p1vent
alcohol
sugar, salts etc Lodine.
carbon lisulphidesulphur turmentine
benzene
toluene carbon tetra-
chloride
mercury
phosphorus
paint. oil. rubber.
qils.
PUMS Frease.
many metals.
A anturated solution of a solute at a narticular temperature is one which contains as much solute as it: can dissolve at that temperature, in the presence of the crystals of the solute.
A suberanturated solution is a solution which contains more of the solute than it can hold at the. temparature in the ptasence of the crystals of the solute..
E. Suspensiono
A suspension is a liquid contain- ing small particles of solid which are spread throughout it and which settle on standing.
The differences between solution and sustensions can be summarised as
followɑti
Solution
Suemension
No visible par ticles of solids. Particles do not settle out to the bottom of the solution.
Particles of solute cannot be separated from the solvent by filtration.
Visible particles of solids
Particles fall to the b bottom of the Suspension.
Particlen serarated from liquid by filtr etion.
Solid liquid in which it is soluble.
loaded to a Solid
Solute
or dis- solved solid can. only be recovered by evaporation.
added to a Tiquiá in which 10 in insoluble:
F. Solubility and solubility curves
The solubility is the number of crams of solute dissolved by 100 of solvent at a given temperature is presence of excess of solute.
Solun ty depends;
the chemical characters of the solute and solvent;.
(2) on the temperature, generally
but not always increasing with rise of temperature;
(3) on the
on the pressure..
The way in which solubility- depends on temperature is most con- veniently represented graphically by means of solubility curves in which solubilities are. potted against temperatures. For example, the following figure shows the solubility. curves of potassium nitrate and sodium chloride in water at different temperatures.
Solubility
Pot. Nitrate
Sodium chlori
Temperature
Questions for this week
L. How would you obtain each con-
stituent from a mixture of chalk, sulphur, table salt, "sal-ammontac and iron filings?
2. At 80°C the golubility of a solid
19: 64. At 25 °C 13.5 g of the aaturated solution contain 1.58 of the solid. What weight of solid will he thrown out of, solution if 80 6 of a saturated solution is cooled from 80°c to 25°C 3
3. 45.5 gf a saturated solution of Y at 15°C. rive on careful evapora tion 9.1 g of I. What is the solubility of Y. At this
temperature?