真二第張四第 25
日八廿月正年戌庚曆 WAH KIU YAT PO
郭日僑華
NO英文中學會考試題預習專欄
堅道英文書院主編
化學科
(十八)
CHEMISTRY (18)
SOLUTIONS FOR LAST WEEK
(1. The nautralisation reaction between potassiu
oarbonate and hydrochloric acid is as follows's
#20+ co2f
K2CO2+ 2H01 2KG1 +
Equivalent weight of HC1 = (1 + 35.5) = 1 Therefore normality of hydrochloric acid used
5 = 36.5 0.1370
Since at neutralization, Hormality x Volume
Constant
Lezators, normality of the potassium carbonate Molution
0.1370 x 24.5.
-0.1343.
Sinos equivalent weight of potassium carbonate
(2 x 39.1 + 12 + 3 x 16) 2
- 69,1-
Thus total amount of potassium carbonate. 250 of the prepared solution
0.1343 2.32
250 1000
69.1 gm,
Therefore peroëntage of potassium carbonate in the ash
2.32
*Z:100
[= 4.78;
Pure quicklime is prepared in the laboratory by igniting calcium carbonate or calcium nitrate a platinum ornoible. The decomposition is a Zeversible nation's
四期星 日五月三年〇七九一展公年九十五國民華中
育教僑 M
鐵 中文中學會考
考試題預習專欄
***
This reaotion accounts for its use as a component. of gunpowder and fireworks. It provides oxygen to the other componente, sulphur and charcoal, oxidising them quickly to form large volumes of" ulphur dioxide and carbon dioxides the sudden increase in pressure due to the games accounts for the force of the explosion. It is more suitable than sodium nitrate, because it is not deliquescent, retaining the gunpowder useful over? long period of time. Nitrogen is an essential element to the plant, since protein synthesi requires it in large quantities. Usually nitrogen is available through the soil as nitrates, nitrites or ammonium compounds. Sodium nitrate is used to a large extent as a fertilizer. This is because it is a very moluble salt, whereas potassium mitrate is much less soluble in the cold. The difference between the two nitrates is the difference in potassium and sodium ions. The two may be distinguished by applying flame tents with a platinum wire, A solution of potassium salt imparts a characteristic violet (lilac) flame whereas that for sodium salts has an intens golden coloration.
In addition to the flame taste, precipitation reactions may be utilized. Solutions of potaanium salte give a yellow precipitate with sodium cobaltínitziķe,
3K01 + M« CO(NO2) 6 = K2CO(NO2) ▼ + 3NaCl whilst sodium malta give a yellow precipitate with zino uranyl acetate in acetio acid,
4. (a) When ammonium chloride is heated it sublimes
without melting. However, this change of physiol state is not merely sublimation, but Father a chemical decompositions
NE CINE + HC
} Ammonium nitrite is very unstable and readily
decomposes upon heating into nitrogen and water!
HE NO • 1⁄2 1 + 28 201
(0) Potassium nitrate decomposee
the nitrite on
heatings
203
2KNO2 + 02 ↑
Copper aitrate being the nitrate of a typical heavy metal, decomposes into the oxide, oxygen and nitrogen dioxide on heating:
Cu(NO3)2 - CuO + 2N02 ↑ + 0,
To distinguish between potassium nitrate and nitrite, the action of dilute aoid may be studied. When dilute sulphuric acid le added to the nitrate, no reaction is observed, however, the addition of dilute sulphuria aoid to the nitrite, causes the formation of the unstable nitrous acid which decomposes
mixture of nitric and nitrogen dioxide i
28X0 • 5,0 + NO + NO2
一粒豪气频
英文科 (+7)
LESSON EIGHTEEN
SECTION THRES
ENGLISH LANGUSAGE
COMPREHENSTON
EXERCISE 26
43 70
Read the following passage carefully and then answer the questions that follows:
We got out at Sonning, and went for a walk round the village. It is the most fairy-like little hook, on the whole river. It is more like a stage village than one built of bricks and mortar. Every house is smother- ed in roses, and now, in early June, they were bursting forth in clouds of dainty splendour. If you stop at Sonning, put up at the Bull, behind the church. It is a veritable picture of an old country inn, with green, square courtyard in front, where, on seats beneath the trees, the old men group of an evening to drink their ale and gossip over village politics with low, quaint rooms and latticed windows, and awkward stairs and winding passages.
We roaned about sweet Sonning for an hour or so, and then, it being too late to push on past Reading, we decided to go back to one of the Shiplake islands, and put up there for the night. It was still early and put up there for the night. It was still early when we got settled, and George said that, as ve had plenty of time, it would be a splendid opportunity to try a good slap-up supper. He said he would show us what could be done up the river in the way of cooking, and suggested that, with the vegetables and the re- mains of the cold beef and general odds and ends, ve] should make an Irish stew.
(Three Men in a Boat-Jerome)
(1) For each of the following find a word of similar?
meaning IN THE PASSAGE:
stayed
(b) delicate
(c) rambled or wandered about (d) real, actual
covered
(2) Where is Sonning situated?
beer
chance
talk idly
secluded corner
(3)
Why is the village more like a stage one than one built of bricks and mortar?
(4)
When did the author and his companions visit Soa- ning?
(5)
Why does the author advise people to put up at the Bull in Somming?
(6)
For how long did they wander about the village? Where were they going to put up for the night? Why did George decide to make a stew?...
EXERCISE 27
Read the following passage carefully and answere the questions?
However, the decomposition is facilitated by the fact that the carbon dioxide is swept away by a currant fi sir.
Quickline is a dezanite anemiosl individual, because it possesses characteristic physical and ohamical properties. It is a white solid of fixed. Consity 3.3, it fuses at 2,570 C.
The high melting point and high density of the compound indicates that it is ionie im nature, and mo it is an oxide, it should be an oxide of a metallic element.
Chemically wpeaking, it behaves as a basic oxide typical of a metallic oxide. It reacts with water to yield suloium hydroxide (siaking) which dissolves in water to form an alkalis
CaO + H2O = Ca(OH)2
It also reasts with gaseous acidie oxides forming
G&V + 20% Caso
At high temperatures, it can react with solir noidio ozidën, such as silica and phosphorus pentoxides
CRO + 8102
(30a0 + 3205 × Gaz (PO4)2
As quicklime is known to be composed only of paloium and oxygen, the percentage composition of: oxygen in the compound may be determined through a measurement of the percentage composition of calcium. Calcium is usually analysed as the carbonate. The procedure" is as follows: quickline in firstly weighed, and then dissolved in eroess of water, a solution of sodium oxalate, is addød to the solution until there is no further precipitation of calcium oxalate; the precipitate is filtered, ignited in a crucible and weighed as the carbonate.
From the weight of carbonate obtained, the amount of calcium can be estimated and henos percentage. composition et oxygen in quickline indirectly. found.
Potassium nitrate when strongly heated, decomposes to potassium nitrite and oxygent
2KNO
2KNO
* 021
To distinguish copper nitrate from copper oxide, the confirmatory test for nitrate may be performed. Namely, concentrated sulphurig aoid is added to the reagent, followed by copper turnings. If the reagent contains there will be an evolution of brown gas, (nitrogen dioxide):
Cu +
= Cu(NO2)2 + 2NO, ↑ + 21,0
tratej
If it is copper oxide, only copper sulphate is formed on reaction with the sulphuris acid, but there will be no avolution of gạo,
QUESTIONS FOR NEXT WEEK
Alum crystals (KAL(90)2.1K ̧0) were put into a preweighed crucible, reweighed and carefully heated with a small flame. After the mast has expanded and frothed, a greater heat was applied for some time, after which the crucible waa allowed to cool and then weighed once more. The following are resulta of the experiments Crucible empty - 7.780° ga
Crucible with alum crystals - 9.306 gm. Crucible after removal of water 8.611 gm. Find (i) the water of crystallization content in
percentage by weight,
(ii) the number of water of crystallization molecules in the alum
What qualitative teats would you perform to demonstrate that alus does contain potassium aluminium and sulphate?
Describe in detail what you would observe during the following experiments :
(i) addition of chlorine water and carbon
tetrachloride to potassium bromide solution and abaking the mixture;
(ii) heating red lead to melt and then cooling; (iii) heating ferrous sulphate solution with
nitric acid in the presence of dilute sulphuric acid,
f
What chemical explanations can you give for the
observations? Provide equations where p
W
Iou are given samples of sodium nitrate, ammonium aulphate and calcium hydroxide.
Indicate how you could prepare four different ganes, Water may be used where needad, but no other reagents.
Give distinguishing tests for the gases prepared.
Write an accent of the extraction of sulphur by the Frasch Process.
Describe briefly two ways by which sulphur is obtained as a by-product in industry.
It was a strange ceremony. A pit-tailed twelve year-old girl standing at the top of a hill formed a cup of her hands. Then, aiming her words to the vast open space between herself and the peaks in the dis- tance, she yelled out in German: "Orphans of the world, wherever you are, come. Welcome you here!
She had been facing East as she spoke. Now she turned South, repeating the words in Italian, then West and Worth in French and English,"
Around her stood 185 brightly-dressed, children ranging in age from 4 to 18. Their cheeks were flush- ed and they were obviously enthralled by the simple ceremony. To them it had great significance for they were celebrating the founding of a Children's village in Switzerland.
There was good reason for the ceremony. Only a short time before, these happy, healthy youngsters had been half-staryed and emotionally upset. Innocent victims of World War II, rescued from burning ruins and crumbling houses throughout Europe, their families dead or among the countless missing, they were suddenly transplanted into a world which must have seemed as fantastic and unreal to them as Wonderland appeared to Alice.
⠀⠀ These miserable little creatures had never lived a normal life. To them, houses with roofs and windows with glass were unreal; and it was strange indeed to the inhabitants of this village to spend their nights sleeping instead of running from shelter to cave and cave to shelter, to protect themselves from bomba snipers and thieves,
Now, eight years afterwards, with their war scars healed and their basic education completed, the first growing generation of the village graduates has already taken its place as useful citizens of the countries to which they belong. Having been cared for with love and understanding, these former victims of hatred and pre-
judice are returning to their respective homelands to spread, the message of tolerance and they sow the seeds of a better future.
(1) For each of the following words give another word
which might be used to replace it
(a) flushed
(b) enthralled
(d)
significance
founding
e) youngsters
(2)
8
(c)
(g) fantastio
(h) basic
(1) prejudice.
(j) tolerance.
What was the reason for ceremony?
What kind of children feel they were chosen to live in the village?
Why did the children feel they had entered Wonderland? DA
(d) In what way was the education of the Village
children meant to fit them for life after they had left the village?
ANSWERS TOEXERCISES 24, 25, 26 and 27 will be given in next LESSON.