9) 日二廿月正年未辛慇夏
1991 中學會考預習專欄
明德出版社— MILL & DALE PRESS
Chemistry(23)
Unit 12(Continued)
W. LAM
6. Dry ceil
6.1. It serves as a convenient source of
energy.
6.2.The structure of a dry cell is
shown below.
8:3 Iron rusts Faster in salt water because salt water is a better electrical conducting medium.
8.4 iron rusts faster in acidic solutions because *H* (aq) accelerates the loss of electrons by iron to form iron (II) jons.
8.5 Iron does not rust if it is in contact, with a metals above it in the E.0.5. e.g. Zinc.
8.6 Iron rusts faster. if it is in contact with 3 metal below it in ECS, e.g, copper..
8.7. The diagram below helps explain
what happens during iron rusting,
02 content high
D2 content V2 content
lay
::
- drop of
which
liter
Cathodic
„Pitch seal
areo
(B)
Anod.[c
(A)
Cathodic
Graphite rod las, the ye pale}'':
Mixture of molsted Min02
(to oxidise Hy) and C powder
to reduce internal resistance)
Paste of ZnCl2, and NHC1
tas electrolyte.
Zinc Cas the "wo pale)
6.3 The cell reactions in a dry cell in
use are:
At anode Xn dissolves in the
electrolyte paste.
Zn(s) Zn2+(aq) + 2e ̄
At cathode:
2NH (aq) + 2Mn02 + 26"
black
·2NH3(aq) + MnzOy(S).
H2O()
6.4 Differences in structures of a.new
and a used fry cell
New dry cell
Used dry cell
(a) Zn case is
thicker.
(a) Zn case is
(b) The powder
mixture.
is black.
A
corroded and. becomes thinner.
(b) The powder
mixture
becomes grey .
(c) The paste is (c) The paste may
wet.
1. Corrosion of Metals
dry cup due to
loss water.
7.1 Corrosion IS the gradual
destruction of any metals
due to their reactions with substances in their surroundings, e.g. substances, Cin, ainuta «form oxides or other
compounds.
7-2 Corrosion of a metal is primarity an oxidation of the metal to its The oxide in most cases is oxide:
air and powdery, permeable to moisture, and readily flakes off. e.grusting of Iron.
7.3 In some cases, the oxide layer 15 tough and adheres strongly onto the metal, thus forming a protective layer.
8. Rusting of Iron
3.1 The
corrosion of iron is dre commonly known as rusting.
The must. js reddish-brown
chemically
Fe203*XH20.
represented
and
8.2 Iron rusts only in the presence of
both air and water.
華僑日報
(a) The primary reaction in iron rusting is an electrochemical process.
(b) The part of iron far, inside the water drop acts as the anodic) area while the part of iron near the edge of the water drop acts as the cathodic area
because water near the " edge: contains relatively
dissolved air.
(c) First stage reactions
At the anodic area::
----
Fe(s) Fe(aq) + 2e
At the cathodic area:
more
(oxidation).
用
報日僑等
(a) Which
901
Then will NUT displace hydrogen from dilute acids?
iron nell
(b) Which of them will form the most.
stable hydroxide?
(c) Which of them is most likely to
form Lhe inast stable oxidè?
(d) which of them is most likely. Iound
fres in nature?
(e) Which of them could have its oxide reduced by carbon buti not by hydrogen?
五期星日八月三(一九九一年十八國民藜中
egel plato
-petri dish
(Zn2+). inside the pot which thus
attract the negatively-charged
sulphate ions (502) into the pot.
(e) Yes. The blue colour fodes off
because there is a decrease in the concentration of copper(II) ions due to its deposition on the copper plate.
The overall reaction is:
Zn(s) + Cu2+(aq) ---Zn2+(aq) + Cu(s)
After some time, the following results were obtained.
Iran nall-matal
strips Iron-magnos fum
Observation
{f} Yes,
Gel near magnesium stripi | turns pink.
Cand of
14
Iron-zinc
Gal near zlat strin
-1:
turns pink.
(g) M(Zn) = 65.4 g mol
Iron-lead
Gel. near from all tip
turns blue,
Iron-copper
| Geinear Iron nail tip
turns blue..
M(Cu) = 53.5 g mol n(Cu) deposited =
1
(a) What is the
purpose of adding phenolphthalein indicator into the
equations
-gel?
the
(f) [f mixtures of aluminium
iron(II) oxide
and aluminium(II) oxide and iron are heated separately, in which mixture will. there be a reaction and Why? Give an equation of the reaction. (g) What would you expect to happen if a little powdered zinc. is slowly added into an aqueous solution of silver nitrate and the mixture is well shaken? Given an ionic cequation of the reaction. (h) Name a metal in the above series - which is usually extracted from its
molten chloride by electrolysis. (i):Ordinary aluminium: metal showa little chemical reactivity towards many of the reagents such as water, dilute acids, etc., although it has a rather high position. 下你 Che Reactivity Series.
"Explain briefly why this is $0.
Question 13.2
In the experiment below, a zinc rod is placed in 1 M. zinc sulphate solution inside a porous put: The pot with its
then:placed; cinia Content 15
beaker containing a copper plate in copper(11) sulphate solution. When the key is closed, a current is registered by the ammeter.
Zinc rod
purpose of adding 7. tb) WBatis.
potassium M hexacyanoferrate(11) solution into the gel?.
(c) Referring to the result in I,
explain why the gel turns pink..
(d) Referring to the result in IV, explain why the gel turns blue.
(e) In which case would the iron.
corrode most readily?
Write the ionic equations, showing the changes of iron during its corrosion..
(f) Describe how the zinc coated on iron (galvanized iron) protects it from corrosion even when the zinc coat is broken.
Solution to 0.13.1
(a) Cu or Ag; because it is less
reactive than, hydrogen.
(b) K; because it is the most reactive.
one of the elements listed.
(c) Ag: because. it is the least reactive one. of the elements listed.
02(g) + 2H20(2) +
46 401 (aq)
(reduction)
Copper plate
A X Copper(1) Sulphate
sulphate solution
Beuker Porous pof
(d) Ag. (e) Zn.
to
The reactions above will be increased if. there dissolved ions in water increase its conductivity.
(d) Electrons flow from the anoili
area
the cathodic: to inside the iron plate.
(e) 2nd stage neag
(1) Oxidatio
Fe**(aq)
(aq) to
{aq) + O2(g) +2H20
4Fe3+(aq) + 40H(aq)
Portacion
hydroxide
of
Fe3+(aq) + 30H-(aq)
Fe(OH)(S)
叫
笑
iron("It)
on standing
Fe2*xH20
hydrated
iron(111) oxide. (rust)-
8.8 Methods Preventing from Rusting
(a) Gose/o11
(b) Pain Panel/Plastic coating (c) in latinğ
(d) Galvanising igon (Zinc-plating) (e) Sacrificial rosion
(f) Staiolesser containing a
high perceque
Question 13.1
ONG
K. Mg, Al, Zn, Fe, i, Cu, Ag are the symbols for the elements which appear in this order in the Reactivity Series
or Electrochemical Series, potassium being the most reactive
being the least reactive.
聖類斯·地利亞教育機構
聯合主辦
加拿大教育講座
日期:1991年3月17日(星期日)及
1991年3月24日(星期日)
時間:上午10時正
地點:地利亞(加拿大)學校
香港太古城太豐路 講者:MR. ROBERT J. HUNTER
(MR. HUNTER 為前安省教育 部私立學校主管,現任加國高級 教育顧問 )
何鎮源校長
(加拿大聖類斯地利亞中學) 講座內容:
1介紹加拿大學制及升學概況。
【院士
and
silver
求的
聖類斯
夜校
Mastate thasaretion of the el
flow in the litera Explain year answer.
circula
(b) Write, the ionic equations of thep
reactions: at the zinc rod and the copper plate respectively.
(e) Why mist the pot be porous? (d) In
direction would sulphate 100s pass through
the
the
porous pot?' Explain vour answer briefly,
(e) Would there be any change in the
'colour intensity of
sulphate solution?
Explain your answer.briefly
copper(II)
(f) Do you think the reaction above is equivalent to placing alzine rod in copper(IT) sulphate solution?
(g) if the copper plate changes. its Bass by 2 g at the end of the
what experiment,
change in mass of the zinc rod?
(h) Describe . THREE changes you would observe if the zinc- rod and 1 M zinc sulphate solution are replaced respectively by a silver rod and 1. M silver nitrate solution."
hiestion 13.3
Sur places of iron-nails each coupler With different metal str
tere places
UB
apertritiškos conta hingel wil phenolphthalein indicator arid potassium hexacyanoferrate{111} solution. The hown as in the diagram
set-up was
below..
地利亞
夜校
功課督導班
in the
(F) A reaction will occur
: mixture of aluminium and iron(H)
oxide because aluminium, being more reactive than iron, can reduce iron(11) oxide to: iron.. 2A1+3Fe0 ---- A1:
11203
3Fe
(g) Zing past issolves and silvery 19% of silver are
·This is because zinc the less reactive silver from its solution,
Zn(s) + 2Ag*4 (h) K-
Serraq)2Ag(s)
(i) Freshly-prepared reminium metal is very reactive chemically. Ordinary aluminium is usually covered with a layer of transparent, through
aluminium oxide wAYCA" acts as a protective layer on the metal.
According
Zn(s)
to
the
Zn2+(aq)
+ 2e
Cu2+(aq) + 2e--- Cu{s}
following
n(Zn) dissolved = n(Cu) deposited." change in mass of the zinc rod
65.4 x 35
2.0
9
(h) The 3 changes. observed are:
(1) Copper plate is dissolved.
(2) Silver deposited on the silver.
rod.
(3)Electrons: flow from copper
the
plate to the silver rad in the external circuit. ile.. current is reversed..
Solution to Q-13.3
(a). It is used to detect, the presence of the hydroxide ions. (OH-) because phenolphthalein turis pink in the presence of DH" ions.
(b) It is used to detect the presence
of iron(f) ions (Fe2+) because hexacyanoferrate(111) ions. form... deep blue complex with iron(II) fans.
(c): This indicates that hydroxide ions. : are present near the magnesium strip. It is formed when magnesium
reacts with water and the dissolved
oxygen.
- 2Mg(s) + 2H2O(l) + O2(g).
2Mg2+(aq)
+ 40R (aq)
(d). This indicates that iron(11) jons
. are present near the iron nail.
It is formed when iron reacts with
water and.the dissolved oxygen.
2Fe(s) + 2H20(#) + O2(9)
2fg2+(aq) + 40H-(aq)
(e) Iron corrode most readily in
because iron is attached to a metal Tower in ECS, i.e. Copper. The ionic equations of reactions involved are:
IV
the
育體 B
早達成瀬望 - 正如其榖綠黃文世所言,今使不
馬天尼
歌陽應慈 基 亞
好成荼。
,所以馬天尼
最大的收穫了。馬天尼是排在榜末,共賽十三 今仗爆冷機會不大,如能戍低失球數字,已足 陳慶榮 謝 夫
‘《公民〉・將於今年出發赴京海角逐新原 分別參加女子高級組六公里及女子初級組四公 從祂會代表透露 - 四名男將將參加男子高級組 据卤光挑選送六位港隊成員之香港業餘田
.
份。 的上苯琦、但及午中共天、邨理科工性向身
陳志約
梁承傑·吳誌供
六公里除際及個人賽項·而羅曼兒和陳敏則 明日才可作前日下午十二時四十分起進行决勝局,並且遠取七分反敢爲勝,先拿下首
賽事,因此港隊各隊員對我道認識不多,要待 由於今次的亞洲越野長跑錦標賽僅躺首麗 -適應賽道環境。男女子
領先,但克好靠强力反攻,速取四周,追打 排名十一的小卡,先三比零,再五比二. 因姬緣以六比四,六比三薪打敗。
· 週三唯一受挫種子爲澳洲寶勒絲,讓英
杜姿雅、姬恩絲、胡芭等亦晋级。
仗,一勝酒和八負,只有七分,護級的機會,
黃國榮
里賽。次比賽參賽國家中以中國,南韓及佔激戰。
中華僑教育
-王
科大美加州大學辦 兼讀工管碩士課程 九月開課逢週末上課名額 60 作」,希望能盡快能滿足協會的部分要求,但至於薪常會報告器的決
期三年,每年有三個事例 百得文,為他的1A (特點一由
人士、經理及主管級人員。 課,逢星期六上午九時至下午五時上課,預算招收學生六十人。的增加宀百分之一點常 芭現存的設施,以配合 飛讓制課程的核心科目,與全日制課程相同。招收的學生對集滿事·四)。道樂也本未能盈教育學院的發泵;白重 作計劃是開辦無諳制工解管理學碩士課程。懲課程將於今年九月正式開 預算開支,卻沒有多大加教育學院的撥款來改的資助。 安德森工商管理學院簽署的(文化學術合作協議》,其中一項主要的合 但就教育學院本身的裱們强烈要求政府:一爭 新檢討政府對妝育學院
文作答,中文
中文譯本委員會
聽-增進學帶。 的工商管理學院均務米到世界最先進水平。
日・夏季只教授一個科目。通常的安排是周六上午教授一科-下午赦罪的漠視。 科及研究課程。在課程設計、招聘牧師、教學及研究等方面,科技大學枚,以改善教育學院的移學校的工藝與 香港科技大學的工商管理學院共有六個學系;計學系、財務學的影响, 故我們不斷里島文法中學的一 果汁 系、經濟學系、蔣業資訊學呆、管理學及市場學系等。各系均開辦本求政府在短期來增加散 般科目和職業號 有意攻撞上述黛雅射媒程者 - 可親臨九龍廣東道七號環球航運中心 然而政府財政預 八十二套中文課 的再家及專業人士前來演講,好予學員有機會更廣泛地没取各方面的厚 教育學院缺乏資源,而之中學中文課本 授一科,中午則安排工作午餐,邀鷸工商界名人、政界幀袖以及各方面 1 向以來,我們就向政府建議推行 |算案中,對教育學院的本。
資財及設施。 下,且然是在減無坩, 九二年高級本員商將舉行 資助,與通脹率相比 配合一
劉缁資增减有著極嚴重|瑍點計畫,先後 實用科目北出版
彎
月派發予各中學
的中文參考書 於高級程度,課 接錄製成小泰 為使中學校
委爾把適用" 一並於去年三
長及教師對上述
五字樓索取詳情- 或致電217912
( 四間教育學院學生會
- 中文蹀 的錢藏
箕,詳情如下:
從以上兩點來看,事行,時間馬:定於本行至下生命
Solution to Q.13.2
more and
(a) The electrons flow framed to P.
It is because electropositive topper herice has a stronger tendency to lose electrons. (b) At the zinc rod:
Zn(s)
At the copPVA
LIBRA
Ze
Cu(s)
The pmust be porous to allow the to make electrical electrons
Contact.
(d). The sulphate ions would pass from the outside to the inside of the porous pot.. This is because there is an excess.
of positively-charged zinc ions
動行師講院學育教
持支會生學國富羅:
【卷訊】四間教育|以下之聲明:
求
黼生協會對政府 學院學生會就立法局首 雖然整個教育部份我們認爲政府對改善教 時;十五日上午九時至下午五時,十六日上午 指政府漠視師資培訓 我們對此表示強烈不考試可以溫用中
的話,態會對此是表示
的甜铗質素和 氣,從而提高教育學院 寶學院講師的工作 升機會,真的能提高教 講師的薪酬或改善其靈 爲 - 若果增加教育學院
的路向和對政府的要
·立場亦貫徹了該會以往 三、最後,該會認
求,深表贊同,而湛些 教育有長違利益的 院的地位]等對社和 質素」、「提高教育年
難以接受的。 育學院資源以提高學 宓曾中有提到「改裝」[ 1、認會對於講師
講師的薪酬及報 理,涵情是表示不滿和
·環因下-對教育學院 次政府——若基於這個 代的一焄的話-那是 是小数的一羣或可被取 象又是一些被政府認爲 「剪」,而「開刀」的對 務貝的程利進行「開 緊縮政策,而對營
帥,有以下之聲明: 一、若政府基於其
支持的。
質
展覽地點爲枯黃洪教育學院过觉,八成)
由經驗敎師指導及督促學生完成學校每日指定家
課,溫習校內所教課程和準備校內及公開考試, 並提供有效讀書方法,培養學生學習興趣,以鞏 固學業基礎。
班級:小學 P.1-P.6
中學 F.1-F.3
上課地點:香港西區第三街179號(聖類斯夜班 )
香港鰂魚涌太古城(地利亞 )
546 0288
568 1134
2 有關在加拿大及香港入讀加國學制中學
342 2289
389 3289
743 9313
( GRADES 10-12)詳情。
歡迎各級同學聯同家長出席 費用全免
預留座位 568 1134
九龍官塘月華街19號(地利亞) 九龍官塘協和街223號(利瑪)
九龍美孚百老匯街80號(地利亞)
上課時間:逢星期一至五 晚上6:00-7:30或7:45 - 9:15 報名時間:星期一至六 上午九時至晚上九時
[中文课本展
驗的投目期
覽展本課文中
行舉四十月本
Stage 1: Fe(s) → Fe2+(aq)
2+
+ 2e.
Stage 2: 4Fe2+(aq)+02(y) +2H20 ( 8 ) -~-~-~-~
4Fe3+(aq)+40H-(aq) Fe3+ (aq)+30H* (aq)--- Fe(OH)(S)
on
standing
Fe2O3"×H2O. rust(hydrated tron(III) oxide)
(f) Hiven the zinc coat is broken Iron will be exposed to air, However, since zinc is more electropositive. than iron and has a stronger tendency to lose electrons to form ions than iron, so, iron remains unchanged while zinc is oxidized to
zinc(I) ions,
作安
Zn2+(aq).
【特訊)香港科技大学工商管理學院與著名的美國洛杉谜加州大學
四月六日至十四日
教育主任(等同副校長)的說位, 理化與教育主任間的比例,以及有否可能生班耿求多的學校增設高极 ,讓會長蔡染髮指出,教育敕早前函説衡,表示會考点現時明
定,則屬中央政府之事,教器也無能傷力。
如計劃般採捽做非教學性工作的初步工業行動 í特跟)官立中學學位人的協會今日舉行特別商科大 - 決定是否
他說,教育署署長李越捉在日前與他們會議,送踞斁署已「進行了
官中學位人員大會決定 是否採取初步工業行動
李越挺謂教署已『進行工作』
粉足球場
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