・
27 MAY 1970
ITV
1*6* *=*^# D=DAOFLER, WAH KIU-YAT PO
&#
僑.
434
英中會考化學科答案
堅道英文書院撰答
#$%$#$%$#$%$#$%$#$%$#$%$#$%$#$%$# 5%$#$%$#$%$## $¥£#£££%$#J
Suggested Anaveza
of
n.k. Certificate of squcation Examination (English,
CHEMISTRI (CONVENTIONAL QUESTION).
•(a) EXPERIMENT I
When concentrated nitric acid (HNO, was added
to copper (Cu) a pungent brown gas was evolván. Bad the metal dissolved to form a grear Y aolution. Copper was oxidized to the cuprio state yielding cupric nitrate solution (Cu(NO3) whilst a portion of nitric acid was reduced to nitrogen dioxide gas (NO2)))))
Upon initial addition of sodium bicarbonate
solution (NaHCO), 8 colourless, odourless gas of carbon dioxide (CO2) was evolved and the
small excess of nitric acid was neutralized to give some sodium nitrate (NaNO,)
Further addition of the bicarbonate solution slee produced carbon dioxide, but the reaction was with copper nitrate. Thus the formerly green solution became colourless with formation of a thick blus-green precipitate of oopper carbonate (CuCO2). At the same time more sodium nitrate is formed.
After evaporation, a greenish powder of copper carbonate and a crystalline mass of sodium nitrate remained.
When these contents were-strongly neated, coppe carbonate decomposed to carbon dioxide gas and a black powder of cupric oxide (Guo). If beating is strong enough, sodium nitrate will pelt and decompose to oxygen (0) and sodium iitrite (NaNO).
EXPERIMENT II-
d
When Iron (Fe) was heated with dilute sulphur acid (8,504),
It dissolved with evolution of colourless bāğurless hydrogen gas (8,) and formed a green solution of ferrous sulphate- (Feso). This is also a reder reaction.
When
small excess of ammonia solution (NH OH) wam „dded, -the medium became alkaline so that 'errous hydroxide (Fe(OH),) was precipated and ihe solution lost its colour.
Pure ferrous hydroxide is "oolourless, but rapidly turns green and then brown as it is sasily oxidized to ferric hydroxide (Fe(OH)3) The solution thus contained ammonium sulphate. ((NH),30,).
Upon filtration, ferrio hydroxide was soparated from the ammonium sulphate solution.
(b) Notallis copper from cupric oxider
The residue from Experiment I is washed With water and filtered to remove any sodium nitrate or sodius nitrite. The wat cuprio oride is dried by heating and then placed combustion tube in the rrangement abowni
Hydrogen
wakh bottle
Conc.
cupric oxide
stean.
combustion tuba fishtail burner
Fairly para nyarogen gas is generated from aluminium and sodium hydroxide, passed through cond. sulphuric acid and them into the combustion tube. The cupric oxide is strongly heated, and is reduced by hydrogen to metallic copper, whilst the water formed escapes as steam. excess bydrogen may be burned.
Any
Teat for the presence of sulphate sons's To the filtrate obtained from Experiment II. dilute hydrochloric acid is added till the Bolution is soidio. Barium chloride solution (BaCl,) is now added. A white precipitate of barium sulphate (Ba50) will be formed,
indicating that sulphate ions are present.
報日橋
2.(a) (1) Relative speed of decomposition oz nyarogez
peroxides
Landolt
tube
water solution of pure hydrogen peroxide decomposes very alowly at room temperatures but even traces of many substances markedly increase the speed of decomposition.
21202
2020 + 02 1
To study the catalytic effect of mangannas dioxide in this case, a simple experiment may be done as follows, A Landolt tube which is usually used in the laboratory for illustration of the Law of Conservation of Mass may be successfully utilized here.. The tube contains two limbs and is shaped like a inverted.
To one limb, some manganese dioxide in u. small tube is carefully introduced.
other limb, a commercial 3% solution fo tho
of
hydrogen peroxide is placed till half full. The mouth of the Landolt tube is fitted with a delivery tube leading to a trough water, so that any gas evolved may be collected over water.
retort stand
Delivery
asuri
cylinder
E shive shelf
lindar snutend of an ordinary
order 40 k-.* an idea
Bjøre used here
of the volume of gas evolved. At first the Landolt tube is positioned so that the contents in the two lams cannot mix and allowed to and for Boms time (1 hr.). in elmost negligible amount of gas may be evolved and collected.
Next, the tubs is rotated 90 degrees so that mixing occurs. All at once, far is observed to evolve rapidly and collected is the measuring oglindar. The volume of ga collected ovar suitable time interval may thus be recorded. The gas evolved is testad for oxen, by meani of a glowing
splinter.
(11 Change in wight
Bo show that there is a doorease in weight due to loss of oxygen in the reaction, the similar Landolt tuka may be used. However ca weight changea are small, fairly!! Locurate meza urements must be parformed with an analytical balance,
To a Landolt tubs, hydrogen perioride Lolution and manganese dioxide are placed in separate limbs as before, This. in carefully weighed, and counterpoised by a ciniler tube (but no content) for the other side of the balance to eliminate eror due. to buoyancy effect of the air. Both tube aca not corked, so that any gas may escape. The solution and catalyst are mixed by tilting the tubs, After reaction slackene, the tube is again weighed, and will be found to be lighter.
(b) Singa FV - 22
Therefore normality of the resulting alkaline solution used for titration
0,3 x 5.10
50
fherstore number of 8. equivalents 250 ml of alkaline solution
5.10 50 0,00204
250 1000
the
Total number of ga. equivalents in 25 ml molar NaOH soln,
1000
0.025
Thus number or gn. equivalente reacted wi ajonium chloride.
0.025 - 0.0020. -0.02296
This is the same as tae ga, equaVALON UD. ammonium chloride, and thus weight of pure. ammonium chloride -
0.02296 x Eq. wt. of NH Cl 0.02296 x 53.5.
Thus percentage purity of the given sample
0.02296 x 53.5 ± 100
1.40
87.02
P七十月节年〇七九一曆公年九十五颜民華中
英中會考化學科試題
CHEMISTRY:
CONVENTIONAL QUESTIONS
Time allowed. One hour and fifteen movies
Answer inKEE questions only
Give labelled diagrams, chemical equations and structural formulae where appropriate (Atomic weights: H÷1 ̧N=14, Cl»35-5, C=12, 0=16, Si-28, Ca=40, Fe=56)
A student, conducted the following experiments:-
EXPERIMENT I He placed a small piece of copper inetal in a beaker. To this he added a small excess of concentrated nitric acid. When the resulting reaction was complete he added a small excess of sodium bicarbonate solution. He then transferred the contents of the beaker to an evaporating basin and evaporated to dryness. The basin and its contents were then heated strongly
EXPERIMENT IT He placed some iron and dilute sulphuric acid in a beaker which he heated until the metal was dissloved. He then cooled this solution and added a small excess of ammonia solution. The contents of the beaker were then exposed to the air for a long. time and finally filtered.
In each experiment give a brief account of the reactions which occurred, naming the chemicals: formed and stating any colour changes.
(b) Describe briefly what steps you would take
()to convert the final product in Expertment I to pure metallic copper;
(ii)
to show the presence of sulphate ions in the filtrate in Experiment II (NO EQUATIONS ARE REQUIRED IN THIS QUESTION)
(3) A student sets out to investigate experimentally the catalytic action of manganese dioxide on hydrogen peroxide. Outline experiments he could conduct in his school laboratory to investigate the following:
(0)
The relative speed t which hydrogen peroxide is de composed with and without manganese dioxide added (There is a change of weight when manganese dioxide
and hydrogen peroxide are mixed.
250 ml of a 10 molar (1:0 nomal) solution of sodium hydroxide was_placed in a flask. 1-40 gm of an impure specimen of ammonium chloride was added. The flask and its contents were then carefully heated until no more ammonia gas was evolved. The resulting solution was found to be alkaline and was diluted to exactly 250 ml, 50 ml of this solution required 5-10 ml of 01 molar (0-1 normal) hydrochlar acid for neutralisation: Calculate the percentage purity of Lie original impure ammonium chloride.
Starung from pure ethanol describe how a small quantity of fairly pure water may be obtained in the laboratory. Name one chemical test and two physical tests to indicate that the substance formed is indeed water.
In the form of a table state the conditions, observations and relative rates of reaction when the following metals react with water
(1) calcium
(ill) scanum
· (1) magnesiua, Based on these observations arrange the three metals in the order of activi***
(c) Describe briefly the reaction between sodium and pure ethanol
Compare this reaction with that of sodium on water
Many metals are prepared on a large scale in industry by the chemical reduction of their ores. An important example is the preparation of iron from haematite (FeO3) in the blast furnace Describe briefly the chemical reactions which lead to the formation of iron and a fusible slag from this ore. Draw and label a sketch of the blast furnace
A specimen or tron ore was found to contain 36% of haematite and 20% of silica weight. If 1,000 kg of this ore are placed In a blast furnace and reacted, calculate
the weight of fron which will be produceds
the weight of limestone needed to turn all the silica into
slag.
Two volumes of hy drogen were mixed with one volume of at unknown gaseous element X in suitable apparatus. When exposed bright sunlight, vic.. it reaction occurred After cooling, the mixture was placed over niercury and no change in volume was seen. When placed over water, two-this of the mixture dissolved. The residual gas was found to be nydrogen (All volumes were measured at the same temperature and pressure.)
Show clearly how this formation can be used to deduce the formula of the product of the violent reaction. State any additional information needed to obtain, u formula
(U). The gaseous mixture formed after the violent reaction
had no effect on dry litmus paper Wer aus paper was, however, tarned from blueto red. Give an explanation of these facts:
Describe how a mixture of carbon monoxide and carbon dioxide may
separated by a chemical process in order to reasonably pure specimen of each gas. Diagrams
obtam
of any apparatus used are not requned
者 第準尙
注頁四息有
意請張刊教
讀第在育
一加 叙,用十五
殺,緻理各同穈坫曾參
GENEVORDE
ES-SEVICES
四〇八八中幣購,六
杰·新界··0四〇三五
<<BBEH - RK
啟事: 生一马英中會考生上,七零年廿五日。」 否算盘正荷,更希儘速公假。此險育司簡娜先 會,ㄓ希敦育豐育正視此事。至於德五年一任是
ERKSEUN..
|專上學聯會舉辦 市政局問題講座
RETER-NAMEUR - ZENS.
·凡者,應注台所指定之日期,前往學校調鼠,並 迎於本星期六(日)卽可接獬,凡攤得安面道 HERE-TEKRY CHERTECE - » 「工作,現出各區官小校務加案工作,根据年度
[十一日至廿三日,接受辦理中湖手崱,初步院随
投考官小學校學生
·初步入選者將指定日期約見
本週內接通知書
<新翠西凵素九及新界之官立小學,於本月
八一直寫,勿析高,8一類崗两面, (11)FUCKUSTUXER (FOR),
·公社舉行
第一次定本月底假大專學生
HAKKER. TIKERNERE 破时之活動,包括两次一鈞大律師。 鄉镪一連串在陽市政局 民之關係:講員! 一直如將堅,及一次爲期) 東 東
一上區坐對市政局織之| 鴻烈大律師 認識及現况之瞭解,特:四、民選議與市 席一事,爲喚起 港團一其選舉之方法,讓! 生之市政局民跟蹤勛退三,市放過成风及 | 衆生聯合就三月三日 關係,將負小馬超阱, 一時舞,香港傳上一面及其與港府各部門之
‘局改革之意凡。
學同範師莞東
餐聚慶校行舉
師東常
◎函來者卖(
洛興