1990-01-19 — Page 9

9)育體:日三廿月二十年巳己意:

1990 中學會考預習專欄

明德出版社,

MILL & DALE PRESS

Chemistry (16)

R. Che

Unit -Revision notes on Electrolysis”~

1.

Some Basic Terms

1.1.A conductor is a substance which

electricity, can. conduct metals, graphite, etc.

e.j.

1.2 An insulatur (non-conductor) is a substance which cannot conduct electricity, 2.3.

covalent compounds, etc.

gon-metals,

1.3 A metal conductor of electricity allows free electrons to pass through readily without itself undergoing any chemical changes.

1.4 An electrolytc is a compound which, when fused (molten) or dissolved in water, conducts electricity and is at the same time decomposed, e.g., Tonic compounds and the covalent compounds that ionize in water such as HCT.

1.5 A non-electrolyte is a .compound which does not conduct electricity in any state or when dissolved in water,

covalent most

compounds.

e..

1.6 Electrolysis is the decomposition

of

an electrolyte, in the molten state or

solution, aqueous

by passing the electricity through it.

比实及六比二。. 梅智勝加拿大旅拿遠二比六,六比一,大

低我,我有機的+] 一.基斯坦說:「乖巧熙未有出声,但不要筠

炸至十三位,性亦認為大家小要以爲伙没有年

··世界第一韋调,安平成风,排名

啟料來更具信心。現在更爲欣賞宮己的球夢 "

田瑰詩意 演员表情自然得體。

胡福特此第四天的爆冷者。 三,大比二及七比近;而史雲生明瞭十四地插

·瑪利洌校的共鋆嘅收 宮

·胡麻特挫十一戱和子蘇颢切斯钻柯夫比

澳洲胡廨特與瑞典史雲生,

浙上午校 快樂的小伙伴(下)。

小學低年級組中國舞甲級獎:德貞小學 淘氣小金魚(上):蘇

2.2 The diagram below is a schematic

set-ug 'form -carrying out the electrolysis electrolyte, X*Y":

ter

on

In the External Circuit Conduction of electricity

Within the Controlpru Baduction cialiste ees is due the coracao) napi ve fars.

herfst slectr

Ancde

When the

simple

鸪蘭特

勝加拿大和斯頓成。” 以六比二,七比五及六比三

Wilt slectrolyte

consisting of

neh the los

the

is key ciased electrons begin" to fiow from the anode to the cathode through the external circuit.. As a result, the. cathede, becomes negatively charged- due to an accumulation of electrons there white the anode, being deprived of electrons. becomes positively Teharged. However,

are

within the olten clectrolyte, the positively-charged tons, x*. attracted to the cathode and the negatively changed. Tons, y, are attracted to the anode. That is why the positively-charged ions are called the cations end the negatively-charged top are

anions.

When the fons reach the electrodes, chemical changes take place

the

At the cathode, each cation gains an electron from it and becomes a neutral atom for radical) again. Thus, the reaction at the cathode 15 a reduction reaction.

ፌ

At the anode, each anion loses its extra electron

also becomes a radical) again.

to the anode and neutral atom for

Thus, the reaction at the anode is en oxidation reaction.

*"

This giving of electrons to the cations oy the cathode

the taking of electrans from the anions bry the ancde keep the current flowing in the circuit. The atoms (or radicals) discharged at each electrode may combine ih

give the more stable

another 切 forms.

一個印度基主能。

·基斯坦以六比一,四比大,大比三,六此

韋谢特·十六號棒知。 其心獲勝的種子疎生有五號基斯坦,只號:

報日僑華

来决心尖鬨及手中奪得今年首次滿貫冠和 現旗对布道“关國公笵慧港加今次看一五出,而文通高娃則以七八八六、六

• 美國洛維遜以大上二、六比其挫芬蘭的

世界第一。20

. 耪、背心六四、六四美陸

小分接近。」 碧加說:「去年我的説價比他好,但彼此一同他对的。

兩屆澳洲公開賽冠軍的三远和一冠道 「他Ç爾焚)已椁醇粲三年,張翰到找了

號種子战雅芝華殿柱,柱學姊最近在澳洲的第 比利時華莎受以七比五、大比!冷;十

艾您

一露絲 ̇督爾班:ㄘ四號種纟阱荷蘭芭甘七 浴蕤、六栂) 三次問-芝華录 先後在布里斯班爽雪梨珓比六(上),六比四,而芝芝·費南迪被 以六、七比六八七比四)京絲貝斯

|對他{黠影响也没有。 及六比四海八衲迈德居住,並且表示所减 : 艾牌的凄厲發球;温说六比二,太

街小 回家路上八下) 小學低年級組中國舞甲級獎:胡案資上午校 西藏(上);海

問:他說:一我感覺很舒说,我

Cations

Na

谢

Increasing ease of discharge

Anions

(b) Relative concentrations of the

jons

ion

higher concentration is more readily.

An

at

2

discharged than one at a lower

concentration. Sometimes, the

七比六(七海四),四六及六地二打妝造 氏四十二度)的水上温度下而在,以六比

均末超越過半準決,令次在華氏喀痰在女華動,問九十二强。

当稻子称色天,

莎巴天妮 ·以大比一,六比一輕取

哈靜與規定。

「我合仗發虛汗,卻越對雙方出一張同仁

; 說:「天氣這必點,就科保持

對戰遊記生。」談到风格衍英一较高下問雌 她說:「我姓得自己比第一場打得好,高

.... 上週在新西湖公開賽奪得冠軍的戴樂斯· 一段使恐据精神不能集中二萬,但我剧照舊上冯比賽,不怕風格拉芙蘿 「我想大多數球員都自對港格拉芙作賽,

五期星日九十月一(〇九九一)年九十七國民中

湘娶第三輪。” 酷炎,打聽美詡史威戴维斯·麥入澳洲網球公||| 这位世界排名第二的的西越好手,前兩屆之在上將球拍蛄断 · :: (美聯社岛西區十八E).想抓進四国料于美国吉利亞二比六,六出二十六比三六比

·切斯諾柯大米熊習慣他的斯伯,以致挫折. ! 祖诺冠軍的二

艾堡適應大熱天輕取西德居能 莎巴天妮不怕與格拉芙再較量

碧加說心靜自然凉 以四盤淘汰戴維斯

澳洲四十二度酷熱作賽

具神韻,動作熟練且流暢。 :眞譯啓學校的孔雀舞麟

porcentration; ceffect is So

· great that it may reverse the order of preferential discharge as indicated in the ECS, e.g in electrolysing cong. Nat(aq), the chlowice ions 401) are discharged in preference to the hydroxite Tons (OH) though Out is above C1 in the ECISE..

(c) Nature of electrodes

The nature of the electrodes may sometimes affect the choice of the ions for discharge, vafið: hence the products Of electrolysis. For example, Hy is obtained at the cathode ff. electrolying dil MaCl(aq) using platinum electrode, but. Nais obtained

using.

mercury cathode because Na discharged combines at once with mercury. Lo for the sodium amalgam.

4. Suitnary of Results of flectrolysis on Several Typical. Electrolytes

Name of the substance liberated

Name of electrolyte

| Cathode off Anode off

Malten

at cathode

Graphite Graphite Lead

at anode

Bromine

(grey.beads)

(reddish

vapour)

-Pb(e)

28r(aq)

Platinum Platinum Hydrogen

2H* (aq) + 2e

Dil HS04

Q1 MaDE Platinum Platinum Hydrogen

24*(aq) + 2e

Dil

NaCl(aq)

Graphite Graphite!Hydrogen

2H*(aq) + 2e

+4e

A.

Remarks

(b) Purification

KARAW

metals such as copper, lead.

(c) Plectroplating..

(d) Manufacturing of NaOH, Cly and HCl (ac) by electrolysing brine solution.

(e) Anodising aluminium.

5.2 Purification of copper.

Spent

br Fro

Pure.cooper shoot-85

ha cathode

Saturated

Qu(aq) +

有體 日三廿月二十年日己

年 邂防員。 九八九年亞洲十名 投 選出的一

| 曹鈔南盘;園栱, 计蝽城,南韓,足球, !! 期,中國-羽毛球 - 潾 南華 福恩,台北,田徑,橋園八 口和洋,日本,田徑,姆斯·尤 他們是男運動員橋。 隊名 賽

用馔,金水寧,

中

【朗羅滿華余

尼:華拉懷 根蕪 治英 亨端華

.尼士倫

打斯唐泰

花

阿比

·鄭任安

「

「港海警星東愉花

蜜烽察路方圍花新華名

九九九九九八十九八赛

下

二四五六七脚心

1.1 ·

11.

二○和

五六五五五〇三一

「八七七八九十三五二

带输

八至一月十八日止)

利 - 整改近况平平的星岛e: 釺華特汌盟 - 故怡有放棄中國和诗,岛因和來世,邀得 從近战仗來看,明顯有漏洞,出於麗新已邀而大中

十十二廿純

甲級獎 圭特殊學校中國舞 東華三院 送鮮花給親愛的老師

·小鳥飛吧

|六七八八八六七十一分

陳

四分也不容有失,但他們的支力並

· 星島

本除今晚可能列体如下:

.瑪利海

【 港會

乙級獎

·和高寺 雅 波倫

王棕綳 胡塭國

東啓:

華

日

主要突出-風格明朗,節日氣氛很好。演員天此可愛,台風大龙图 蘇浙上

合作良好,身乎不俗。 回家路上六甲級獎

加些吸收體可思想。”

布穀鳥(甲級獎

·金 齊一乙級獎〕 ,演出大方有明荣。如能在時作和圓形模化中改善則發現更佳。 一動作設計,榻排與主題吻合,演員除型整演出投入,金鰺的節葖

相當合拍整齊。如能在舞台調度和置型處理加以改善則更理想。. 舞蹈糯排很有特色,用布裂料叫聲配合動作良好。狗展的台展不俗 主題突出,風格明朗,獼褙流嗇。演員莽步輕盈,即必經快,安現 羅亞斯理衛理下

海壩街官立下 胡素貞博士上

快樂的小伙伴八高山族甲級獎

童年樂〔乙級獎 ) 挽耱線甲級獎)

稍-

沛。如在蚴作的設計更豐富些,效果秆更佳。 好,橫山認此努力,節奏明快。須在幹器動作上加强以幾富演出。

· 舞蹈染排意念與主題團台 - 誦能去墓此你柔的一面 - 演員合作良 . 捽紙的主鎗突出,服饰鮮明,演縠作整齊,活潑有動怒,舞來感 道慈佛社搡日霖 啓聲

花梶舞〔乙級獎 配合良好 - 妇能佤5魔貌的醐味則效果更佳。

好,演出炉佳。 一舞蹈編排很合適,演員合作良好,努力粱致。節奏嗎-- 顰蹈版鰱 舞蹈荫具特色,宿風配合良好,麥演投入,自然大方。道具設計很 東華三院啟智

鈴鼓舞(乙級獎

·然,偵認真投入,作具特色。如能在動作的.上加以改善則效果

,演出

美族舞,節奏分明動作整齊。 沙田公立學校 表演台灣阿

is

散育

(retinery).

Impuro

coppor as

coat

the object is

Graphite ancde

Fresh brine

.1.8.An

electrode is а conductor, usually a metal or a graphite rod, where electrons enter or leave the electrolyte during electrolysis.

.1.9. Ag anode is the electrode at which electrons Teave the electrolyte. It is connected

the Positive terminal of the power supply or battery.

1.10 A cathode is the electrode at which

electrons it is connected to the negative terminal of the power supply on battery.

enter the electrolyte.

2. Mechanism of Electrolysis

2.1. When an electrolyte is fused or dissolved in, water, the resulting Fiquid would consist of mobile ions, moving.. constantiy. randomly in the liquid.

but

3.

Factors

affecting

discharge of ions

没

When there are more than one types

手机 of cations

anions voltameter, usually one of them is preferentially discharged. Such a selection of ions for discharge depends mainly on the following three factors.

(a) Relative positions of the ions in the Electrochemical Series (E.C.S.j

the

In general: the lower position of a cation is in the Electrochemical Series, the

more readily it is discharged at the cathode; but, the higher

the position of an anion is, 好 more easily it i's

discharged at the anode.

reverse is also true.

The

the common ions are Some of listed below according to their relative ease of discharge at the electrodes. If all the other factors are the same, an ion will be discharged from the solution in preference to those above, is in the list.

Na*(aq) + H

-Na(s)

Platinum Platinum Copper (or

Hor

deposited Copper)

Copper!

€u2+(aq) + 2e*

̇Braig) + 2e

Jxygen. 401(a)

Voltime Patio of

21120101+02:02

48

Oxygen 40H(aq)

2+20(2Y+O2(g)

= 2:1,

pH increases jat cathode.

Tbut decreases |

jat anode.

Volume ratio of

Mz:D_ = 2:1,

pH increases lat cathode,

but decreases

Fat anode..

Oxygen (with Volume some Chlorine) ratio of

40H(aq)~ H2:02 2:1, 2H_0(2)40g(g) (pd increases

de at cathode,

201 (24)

- Cl2lg}+2e

but decreases jat anode..

ratio of

1:1, ¡NaCH(aq) is

jobtained.

¡Sodium

amalgain is obtained.

Oxygen

F2SO is 40H (ag) --- resulted blue

2H0(2)+2(9) colour of

+4e 'solution

fades aff.

of blue coloration renains Junchanged.

·Cu2+(aq)+2s* Cu(s)

Copper

Copper

Cu

Copper

2+(aq) + 2e

Cupper

I. Intensity

dissolved.

Cord H£) (3q)

Graphite Graphite Hydrogen (or Platinum)

(g)

Chlorine 207" (aq)

C12(9)+28

5. Applications of Electrolysis in

Industry

5.1 Electrolysis is

important technique and has wide applications

industry,

Some important.

חן:

Volume fratio of

2:01:1, concentration of hydro- chloric acid decreases.

examples are listed below.

(a) Extraction of reactive metals such asihe. from:mclten NaCl. Al from Alqūg.

An anode: Cis disso?ves to form'

*(oa), leaning behind Popurities.

Cu2+(aq) + 2e

At cathode, Cu2+(aq) is deposited

as Cu.

Ze

Thus, pure copper is obtained.on the cathode.

5.3 Electroplating

The object to be electro-plated is made the cathode.

The metal to made the anode.

The electrolyte used is a saturated

containing solution

corresponding metal ions.

the

The purpose of this process mainly to improve the appearance and prevent corrosion.

5.4 Electrolysis of Erine solition

Na{p} + {}{2}

-Na/Hg(e) amalgam

When Nag amalgam is run into water, NaOH(aq) and li gas

formed.

M3/H9{ @ j¬ 2H_O(# ) ———→→→ Natil(aq) +H2 (g)

and

combines to give

hydrogen-chloride (HC1).

5.5.Anodising. aluminium

This is to increase the A320,

on the Al metal surface so as to protect the netale

The AP metal sheet is Made the: anode.

The electrolyte commonly used dii H2504

At the anode:

•2420(0) + O2(g)

40H(g)-

● 30g(g)

+ 241(s)

-A1203(5)

1.7 A voltameter or an electrolytic !

cel is d device in which the electrolysis of a substance is to be carried out.

2.3 An electrolytic process

equivalent to a redox reaction, involving a transfer of electrons from the anions to the cations,

Conc

Naci (aq)

(brine)

selective

Graphite Graphite] Hycrogen tor Platinum)

Chlorine

2H*(aq) + 2e">

201 (aq)

~H2igh

Mercury (Graphite) Sodium

Chlorine

Mercury

Mercury cathaca

At graphite anode:

201 ̇(en)

Cip(g)

+ 2e

At mercury cathode:

No*(aq) + e

Nate):

。