頁二第張六第2日四廿月十年萅己曆夏
WAH KIU YAT PO
報日橋
三期星、日三月二十年九六九一展公年八十五國民華中 南教僑華
10英文中學會考試題預習專欄
堅道英文書院主編
化墨科
SOLUTIONS FOR LAST WEEK',
CHUMISTRY (5)
(五)
L. The chemical form, which a metal is round in nature. depends on the reactivity. This is indicated by the order in the electrochemical series: K, Ca, Na, Mg, AL, Zn, Fe, Po, Ou, HE AL, Au, Thus the alkali metals and some alkaline earths are so reactive that they never occurred as free element or even as the oxide, but are found as the stable nitrate, aliloride, -sulphate or carbonate. Ores of Al, Zm,
For
Pb may be the oxide or the sulphide in addition to the carbonate, For Ou, Hg, Ag, Au, due to their stability they even occur as "free element although
usually the oxide and sulphide ores a are important.
Dring extraction, the positively charged metallic ions in the ores are supplied with electrons to be converted to the corresponding. neutral atoms. Such a process of: electron gain 19 a reduction. The strength of the reducing agent required is dependent upon the stability of the metallic ions. Thus for reductions up to compounds of Al, the drastic process of electrolysis is necessary. For the less stable metallic ions (Zn onwards) the most economical reductants available are coke or carbon monoxide (from incomplete oxidation of coke) m
Very often, the richer ores are obtained by separation from the impurities. This is usually attained by washing with a stream of water when. the lighter earthy particles are removed. In certain oanes, a mugnetic separator can be employed. Such processes are concentration, processes.
*** The Bulphide and carbonate ores are often given a preliminary roasting in air, for removal or sulphur dioxide or carbon dioxide. The oxides ac obtained are easier to deal with
2ZnS
* 2źno **
2nd + 002
250,
The roasted ores can now be reduced with ooke, Sometimes, by a suitable adjustment, it is possible to reduce some of the sulphide by the oxide.
As the product of the reduction process is
a' pure specimen, purification has to be
At Electrolysia gives very pure metals,
but more often the impure metal is heated in an open hearth, when impurities oxidise and rise ti the surface as a soum and can be removed,
Iron occurs chiefly as oxides in different formes haematite Fe_Og, magnetite Fe304 Extraction consists of two processes, firstly smelting to the crude metal, secondly the refining process.
Smelting is carried out in the Blast furnace, Iron ore, hard ooke and limestone are powdered mixed and pre-heated and then fed into the furnace at the top. A blast of hot air is blown in at the bottom through water-cooled copper pipes.
200
The Blast Furnaced.
400°c
800°C
air blast. iron hole
lue gases (28%co)
? 300 + Fe20g 2Fe + 300g Fe203 + 00→→ 2Fe0 + 00.
FeO + CFO + CU 20+0 200
1600°C= ← Air bfast (5009°C)
→Slag hole.
At the hottest part, combustion of coke to carbon monoxide occurs. This carbon monoxide is the essential reducing agent. It reacfs with férrio oxide in two ways. Fe2O3 + 3
+ 300 = 2Fe ¥300.
is exothermic and reversible, and"adcording to Le Chatelier's principle more iron will be produced higher up where:it is coplar.
Fe2O3 + CO = 2500 + CO, is not reversible, the
ferrous oxide formed is reduded by coke in the endothermio reaction occurring further down, The iron: formed. is tapped as a melt from the hearth of the furnace. The limestone decomposes into quicklime and removes the earthy impuritie as silicate, slage that float on top the iron, preventing the latter from being oxidised, it is also withdrawn. at intervals,
CaO + SIO,
Most of the cast iron from the Blast furnace is refined to remove all impurities. When almost all:the carbon is removed, the produot is wrought izon. The various steels have a carbon content varying from 0.1 to 1.5%. Different refining processes giving steels of different composition are in use. These include the Bessemer process, the Siemens-Martin. Open Hearth process and the electric furnace. The manufacture of steel demands not only a reduction in the amount of carbon and. the removal of most of the silicon in cast iron, but also a very thorough purification from sulphur and phosphorus, Sulphur can be removed by a preliminary addition to molten iron of manganese, forming a high melting insoluble sulphide MnSj but phosphorus, has to be eliminated by the basio lining used in the various processes,
A is a mixture of magnesium powder and flowers of sulphur.
B is hydrogen
C is sulphur
Dis magnesium hydroxide
E is magnesium sulphida
Fie hydrogen sul phide
Qis
15 Lead sulphide
When dil, sulphuric acid is added to A, magnesium reacts with it irgorously, but sulphur is less. behindi
12 + H250 - Meso
Thus the gas B.liberated is hydrogen which
extinguishes a glowing splint but burng in air to etrant
2H + 0.
22
2H O
2
On filtering the reaction mixture, yellow eulphur
C is left as a residue. The filtrate of magnesium -sulphate-in-solution: gave on addition-of-sodium
hydroxide, a white precipitate of magnesium hydroxide, D;
M&SO + 2NaOH →→ Mg(OH),} + Na,SC
This hydroxide is inàoluble in excess of sodium hydroxide.
When A is heated, magnesium metal and sulphur combines irgorously to magnesium sulphide E:
S→ Mgs
Magnesium sulphide reacts with dil. eulphuric acid with liberation of hydrogen sulphide.gae F
MgS + H250, M250 + E¿S?
Hydrogen sulphide burns in air to give steam:ans. sulphur
2H2S
2804
This gas also reacts with lead acetate solution to give a black precipitate of lead sulphide G.
++
2
3. Faraday's First Law of Electrolysia, the weights
of substances formed at an electrode during eleotrolysis are directly proportional to the
quantity of electricity that passes: through the solution.
. Faradayra Second Law of ElectrolyBis; the
weights of different elements formed by the same quantity of electricity are proportional to the equivalent weight of each element,
Volume of_hydrogen gas at (273:+ 15)*K and 740 mm pressure 23.5 0.0.
From gas equation
Thus volume of hydrogen at N.T.P. conditions
740 x 23.5 x 273
(273 +15) x 760
21.69 cld.
Since L gm. molecule for 2 gm, weight) of hydrogen pccupies 22.414 a.a. at N.T.P
Therefore weight of hydrogen liberate
21.69 -22,414
0.001936 gm.
For 'the same quantity of current weight of oopper: deposited is 0.062 gm. Therefore, according to Faraday's Second Law, this weight must contain the same number of equivalente as 0.001936 gm. of hydrogen.
As equivalent weight of hydrogen is 1, thus equivalent weight of copper i
(a) Copper and zino
0.062 0.001936
32.03
Copper is below hydrogen in the reactivity series whereas zinc is above hydrogen. Thus "copper will not react with dilute acids, but zinc: will be readily dissolved. In order to obtain copper, dilute sulphuric acid is addoc to the mixture, zinc sulphate is forned in solution. The copper metal is filtered, washed
4th water and heated to drynese-
Cu + H_50y = no change:
Zm + HSQ; Zrison + H,
Oxygen and dinitrogen tetroxide.
Oxygen is a aparingly soluble gas, whereas dinitrogen tetroxide is readily soluble in water to a mixture of nitrous and nitric acid. A stream of the mixture is bubbled through water, the oxygen. gas obtained. is then pass into a wash bottle of conc, sulphuric acid to dry, and is collected.
+
KNO
HN O P :
It would be better if instead of water, alkali is used for the absorption. Nitrogen and carbon dioxide.
Carbon dioxide is an acid anhydride, thus it can be absorbed by an alkali, The mixture is allowed to bubble through sodium hydroxide solution and then conc. sulphuric acid, and pur dry nitrogen is obtained, ja
CO2 +
+ 2NaOH - Na200.3 + B20.
(a) Concentrated nitric acid and concentrated
#ulphur acid
Concentrated nitric acid is much more volatile than sulphuric acid, and the mixture may be separated by distillation. The mixture is put into a retort and heated, the nitric acid that. distills over is condensed and collected. (e) Sodium carbonate and calcium carbonate
撥作宽谗新校舍及 艾假獎品繁多,概由尅一常挐貼此項粼贴息政府袖助,忠類 加凵a(E)鋀沙?可悲糜參加,但一均無瞭照教育甩例辦理,他军上深校則需邀出
|聖保羅男女中學
粗貼津會師
會大員會
末週
『
道
九
千
本
包
KERK
教
補助及津貼
學校之行政
英國歷史學會主辦
一搭,下午四時請社會名 流邵剂兆夫入、李钧洪
高級教育官林遠在 師會教學研究大會演講
歷史教學研討會
林夫人、岑才生夫人、張
【
"(m)
*
( 二) 津貼則例之內容重點爲何·現行點
末路大會,驚
週末舉行換物會
行換物會,發出款項,,知览名貴房車一座,
質外,並無迎各校歷史科敕參加。 上午由邱仇榮夫人揭幕
琳灣歌手。會後,並在港大食舘泉探離職,除會 將外,到會人士並可分別發言,以便交撞鼦雞及女
本月六日在香港大學舉行 歡迎各校歷史科教風參加
•史科主任李培蒂與海華仁歷史科主任拉斯萊萬一取物品。 | 系講師史帷慣及前任襲阿莫拉材、伊利沙伯中學好者,至祈獨時符合換 日下午三時中起,在两大概史系一一七號激案,下午六時蔽。又找 「 英國運會洪港分會,本月六會當主持抽獎,至 鐵站李嘉陽夫人,利。換物會於录日上午十一眩組教師名參加由學校每年所做收之党安之盈餘支付。. 座生福利之用。此大總會熟心人土潮家長擔牌。大陸聚餐及抽獎,其原則及政府付出落败旨之一半,他一半期
舉行中學六年級紙史教學研討會,除請帶大教育·校負責人維持高級的,而打不受我的愛則需遵守教會前列。 擞總本師、周近鄉律師 | 九酯加士居日常開支。而
乚香港跋師站成裙助則例辦理。 .午四時,在「敕月之薪金作於大部份,其他鵰包括一般外校之
、辯似銘、方網的在一貼學校處私立及官立将他與同一 大批裁決次校由於,古人,一沖貼學校襞會委任。 碧保顾刀女中學,定六、物、游糖、音樂斯唱、勞工行道法例及放映,然說很犯核定之動,她知梭力,及後校方將於車,但可张陌參加)。(C)當任區於讯站返校時其一為之進行,鄧程之編排,教學之選展,厚生器件 一般雜貼學校,蒸園校具,傢俬及悔智機會之用,必須獲得教育司之批准》。 ∴C遣鄜心麥當勞狙],儕備多時,內容有愤。勞工處徐泰湖講述寫明之收支館算,經會計師發吃後,還安本岛铝模,則在例外:(A)臨時教師。(B)乙級效羅(四)津貼學校管理之中心·有關於校舍整
一、朗侯生白光斯雄、青、座,其講題爲「補助及津貼學校之行政」。林氏,生意好,而闊分貼的魔之数字而决定。 ,再除牲講一付一般開支毎一財政年把終結時,必須將一年來 於律貼則例下支薪之及師,必需供款但下列致勝一 本月六日下: A A ) 椰常帶貼 本站舉妝螺襲之支出,少校委會委任心,教育司購其代表,庫務司或其代 此外檠融是由原校免六七月間向政府申請一般公積金之銀行戶口,福特其在機超同销術吏效,處理財政的使用,方能使恐投行政戰利的展開。
·育及院舉行,政府征月貸實補足並加上一項維費津貼 , 以應 洛加供款之教師,必須具有下列慊件:所有,該離啻為代发僱主方面的凹修问题,他可由各校 娜,安武一般律佔展役之經濟來源及等通,例,在华全部供效與政府找過之同樣數字的敗壞,一依照合約行本,故過去教育司本人每年均發出建 一年希已超過五十学者。CD)薄職之歌師(但可
·俄歇辦法黑每月根德罗念之百份之五於支薪
·一邊跟學校接受政府之資助,故此在財政上必須遵嘔計,及死亡時,根據難選學校公積金則例得一條(三)承貼黑校敎瓦之聘用及解聘,根據 汪瓣默默的糖眏鹣决队维,高级狄育官林凶婆主持學校行政部之本質的農家可要根據法校於發盤時,會有難得政府之一在,被該校不再議價官津貼季後時,就没有打 DJ公積金:津貼學校公積金設立的身 的 贴與私立學校不同之地力,及津貼,是他到一艘甲貼學校致師於離職,退休,解第一日,面裝校轉往新校,傳的後級供。
桜方仍需負查非經常津貼額之一半,故此律學 過程,則要遵守律阽則例所規定之程序進行。 一欸安姆入下一年之預算上,如獨政府批消,即 登費:因篇一間津貼校於開辦後, (特供視香也激師分於日前舉行國際研究大的運費質下之其他費用,此項黨對之數字, 雷]供激發師於失萏十年後基職感到達退休 予权歉,此委員會之成诗如下:主席(由津贴學告,測台學校當局應與敦西綻約。"
付出一筇建築費外,其他一切之政府資景及以後之同 項並連同年來分很之紅利。
一,經審查後,如認爲必要時,朗政府將付出之 還教育司 會計組。 時,恐校扣袋,然後將全校總供紋,商接繳交存 負責行政之入荫,必鱟了釋有關之邊序,幷小心
校有被此儁微收堂價,褲檔有楹聯激還投射一年被荷: 1:文,並加上所分派之紅利。 淡,不超過五名之委員,彼等必須屬學教師及,現已進行草琹一標準合約,如怨有關各方面,總 公積金是由一個管理委員會投資管理,及將一面模之校嫩合貸金安,雙方並應簽署合約,俾進
據英国之效,可於下一財政年度迅用。蕙用之談級年所派之紅利若干時,無將氝校監,俾能通 ,換句話說,一般主辦團炎除去舞建學校時帶|算時,讓教師可獲得歷年來之供歇加上政府擬發 「貼用因,所以對於財歌的記錄,需要一定 之培義,校外活動之糝辦,貼學校與私立學校 辦理,並經教育司貓之蕃務,故此染學校
各位同時段會留意到報單上所有開發司
貼剴列附嬴之管理細則敎師之心用及解聘,由
戶日,取泅其新年之共铁及分派紅利之一半。 3敎師轉校時,亦可向教育司署申識將其片
我啟該師設一個別檔案,傳記錄在案,以便每》
公衍念司取诫年於管理委員會年會後,發
孫。"
無由 能項校
蘇聘的,必需之亦
同時
口得數
府,
雙付
貼
不此學
後
。
Sodium carbonate is soluble in water whiley
calcium carbonate does not. The mixture is first digested with hot water, the calcium carbonate residue filtered, and the filtrat concentrated and will yield sodium carbonate crystale on caoling:
(f) Sodium bromide and ammonium bromide
,
Ammonium bromide is volatile, i.e. it sublimes when heated, On application of heat to a. mixt of the two, succeeds in removing ammonium bromide, Jeaving pure sodium bromide behindà
QUESTIONS FOR NEXT WEEK
1. (a) Describe what happens when concentrated
aulphuric acid reacts with each of the following: (1) sulphur, (11) suger, (iii) zinc oxide
What property of concentrated sulphuric acid is illustrated in each case?
(b) Using ammonium chloride as the starting
material, outline one method for the: preparation of each of the following substances
fi) a reasonably concentrated solution of
hydrogen chloride
(ii) a sample of nitrous oxide
If you are given three solutions of copper, a lead and an iron salt. What experiments would you carry out to distinguish which da which? What additional tests would you perform in order to determine whether the iron salt is ferrous ar ferrio?
write fully labelled chemical equations, showing structural formulae, for the conversion of ethylene into
(a) ethane (b) ethyl chloride (c) ethanol (d) formaldehyde (a) acetylene
Indicate the type of reaction that took place in each case.
What is understood by the terms normality, molarity; formality? Give examples to illustrate. 0.85 gram of calcium carbonate having calcium sulphate as an impurity is dissolved in 250 ml. or "normal hydrochloric acid, 25 ml, of the resulting
liquid in found to require 25.2 c.c. of-a solution of sodium hydroxide (containing 30 gm of sodium: hydroxide per litre) for exact neutralisation. Determine the percentage of CaCO in the ominais
之期之