頁二第張六第日三十月正年戌庚曆夏 WAH KIU YAT PO
179英文中學會考試題預習專欄
化龍科
CHEITSTRY (16)
· SOLUTIONS FOR LET, NESK
(十六)
Dalton had tried to explain the sinnie che mi FOTE accupied by the ultizate partioles of gasen (mtode) are all equal, so that a giyon veltas of oxygen gen would contain the nose number of particles QE ** aqual volɛse of hydrogen gas, and so forth. However, be found that tão behaviour of gazet daring resetiens are not always explanable by thane assumption. Tas diffulty was removed vhan Avogadro suggested that the molecules of up slomentazy gas need not be composed of single atoma, but might consissor groupe of piniler atens, corresponding to groupe of disshkilar atoms which for the moisonies of a ocapsund ges. Furthermore Avogadro's hypothesis states that #qual volumes of different gases at the samo temparature and pressure contaža oqual numbers molecules.
To Properties of gason by supposing that the apacak.
In moesgaanço wish Avogadro's hypothesia, one can thus substitute mclocuida tez. volumes is all chemical changes where gaseous elemento and... conpomada arò tavolred. The following reaction hed bean studied
1 volvo 1 vel. (1 mol.)
- Agavegan chlarida
12 vol.
(1 Rol)
[2 RO1.)
Hydrogen é Özygen « steas
2 vol.
(2 nol.)
1 vol. 2 val.
(1 Rol.) (2 mol.}
Kåtragen + Oxygen » Nitrio ozido
1 vol.
(1 mola)
1 vol. 2 vols
(1 mol.) (2 mj.)
Fitrogen + Kydrogen = ÁSZOKÁS ·
1 volo 3 vol.
(1 861.) - 43 mǝl.).
2 vol. (2:01.)
From The above equations it appears that no subdivision of the solesnien of hydragon taken place whas the gas combined with ozygen to fera an equal member of nolecules of water vapour howavez, ško solscules pra obviously halved when one moleculo ef hydregün yields two molecules of hydrogen chloride, or when thrga molecules of hydrogen are dietzfluted squally amongst two malaoules ef ammonia. As no further subdivision new been observed in any reaction in which gaseoUN hydrogen is involved, we conclude that the molecule of hydzegon contains two steze und auslom to it the foxazla Hje
Similarly, it is observed that the molecules Or 027808 and nitrogas azo halved when they 2 coabing with one another to form two molecules of nitric oxide, again as so further subdivision has been observed in other changes involving gaseo oxygen, nitrogsa, žú ža concluded that the molecules of these gases are also fiatosio. "ema
The senplexity or these guBOOKS Bolecules has mino:"been established by a purely physical methodi by sossuring the ratio of the specifin beate at constant pressure and at constant volume, The ratios for hydrogen, oxygen," nitrogen are 1.41, 1.40, 1.49, whilst the xinetio theory of gasen gives 1.66 for a monstasio gas and 1.40 for a distonio gas. These pageous elemente are therefore diatomic.
In the caso or raze gROOM, 0.6. ngon, they do not take part in chemical reactions, and have to be depezdont on physicsl zathods to determÅ NO their atomicity. Their specific heste C /C, is very close to 1.667, the value for a monostorio fas. Hence all the noble gases ozies in the foza of separate atoms -- a unique property for gason at ordinary temperature.
When the molecular weight and the atomicity of an elensatory goe have been deduced by means of Avogadro's hypothesis, is in only necessary to divide the molecular weight by the atomicity in order to get the atomic weight of the element. Thus the ratio of the weights of single molecules of ganes is givon by the ratio or thair densities; and the following zolutiönships are obtained taká, min
O2 = 32, P = 124, 5 - 200
their atomic weights can be deduced ay onGGT
N14, 16. P-31, Bg- 200
chloriza
pozt
- 13 O CĂ, UNG.
mercury cathode
KELLMER SOLVAY CELIA
Saturata.
brina
Jodien hydroxide is manufactured o1uctroly→ tically from aqueoua sodium chloride, oblorino bring an equally important product. To obtain modium hydroxide, anode and cathode must either ow separated by a diaphrage, to prevent mixing of the products (diaphragm call),
), or the osthode may be of mazourg (marowy oell) giving sodium amalgama the Atlas--Belvay cell, saturated brine in elbstsalysed using a carbon anode and merouży pathode. At the cathoda. sodium is liberated and
報日橋等
三期星
dissolves to form sodium amalgan which is with-
·drave from the call and treated with water to give; caustic soda and hydrogen. Two faoters determine that sodium is liberated instead of hydrogen (which in the usual electrolytic product) at the ezthode. Firstly, the very high over-potential of hydrogen at a mercuzy cathode raises its discharge potential considerably, so that it is difficult to be liberatod. Secondly, sodium dissolves in the morowy to give a dilute solution, the electrode potential of such a dilute amalgam is no low that, sodium ions can be discharged. The reaction are:
at anoda
at catande. Ha
201
– NaOH + 13, ↑
(2) Alumisiima is a weakly elsotroposis
it dissolves in sodium hydrogen and forming sodium alv
(3)
241 + 27805 + 620-
element,
-evolving
+382 f
phosphorum dissolves in sodium hydroxide.
• 34805 + 35,0 - PH2+ 35a, P02
PARA Ago phosphine and sodium hypophosphites
(0) Chlorina# 6188cives 15 aqueous sodium hydroxide.
the proizota deponding upon conditions.
In the presence of cold exonsz. alkali. chlorida
andam are forzsás
208*
-014:C200-
+ 5.0
In het solution, chloride and ohlori
kce forasds
608 4
3012
- 501 + C103 + 3020
aba latter may be considered as a dispropor- tionation proosas of kypoohlerito at the higher temperaturas.
3020 ➡ 201 + 0103
(d) Sulpaer Kingoltes slowly, in strong alkali
tive a mixture of sulphite and sulphide Anitially 1.
EZ - - 309 + SE
HOBOVER, TEo svapaide ion can attaon to itself. further stoma of sulphur to give polya«ul phide and so these are found 1055, 908- 2 -→ 3
in solution also. The sulphite ion can add on a sulphur atom to give the thiesulphate iên,
3. Chemical FROCONS, BB for example reassion,
conbusting, nolution, dilution, neutralization, asomieities and bydrogenation are invariably associated with a corresponding energy change. foun a study of reactions should not only include the transformation of zezatants late products, but
But aláb involva a consideration of the energy changes during the processes. A study of thin energy okange oes allusinate tas detail neskaniom of the presoss involved.
In the simplest form, a study or the energy changes REEsolated with reactions is concerned mainly with the evolution er absorption of heat, and is generally known as thormoohemistry. Howaver it should be noted that other form of energy changor To alza important in specific cases, Taus in sa secumulator, chemical reactions relsane Blectrical onsrgy in chemiluminescent reactions, light energy is emitted; and in reactions involving an increase in võlund (ə.g. gas evolution work may be acae in expanzion.
A reaction giving out heat to the surroundings in maid to be exothermic; one absorbing heat from the surroundings is endothermic. The heat change is expressed in calories or kilocalories, and it is constant for a given reaction under a fized set of conditions.
Heats of ramotion are classifiable into many different types, the following examples are the more insortsat ones i
1. Esat at esmbustion, this is the heat change when 1 mo24 of a substance is completely burnt in oxygen. Thus the heat of combustion of methane is 212-798 aal per mole,
4(8) * 2o2(8)
21120(1)
+212.798kcal.
2. Heat or neutraligation, this is the heat change whez 1 gan-equivalent of acid in neutralised by a base, the reaction being carried out in diluta aqueous solution. The heat of neutralization of hydrochloric acid by sodium- hydroxide
2013.7 koul per gran-equivalent,
HC1+ NaOH - NaCl + 1,0 + 13.7 koal
3. Heat of formation, this is the heat, onanga when 1 mole of a compound is formed from åte elements endër stated conditions. The heat of": formation of water is 68.32 koal per mole at 25°0 and 1 atmosphere pressure.
-
102(E) ¤ ̧0 + 68.32 rasi
4. Eoat of atomication, the heat required to convert 1 gras-atom or 1 mole of an element from its normal estate at 25°C and 1 atasemhere into free atoszJAS
B2(8)
103.4 koal. 20
5. Beat or hydrogenation, the heat öhange when. 1 mola, of an unsaturated compound is sompletely. converted into the corresponding saturated compouna. by reaction with gaseour hydrogen.
©234(8) * *2(8) ** C246(2) + 32.8 koal
6. Other specific types of heats or reaction include dissociation, oryetallication, ionisation. The heat changes associated with chemical changes
日八十月二年〇七九一庭公年九十五國民中育数倭蒩
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提出多項建議
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CHEME (YER) THE
THEORYBAERZOETEOR !
對份
other than, PEROTIONS,
mublimation.......
個直是否可能在彼等之商會內設立界, 人性誰經位,以便協助下之會員號個別
(一)與彼等膈下之各商躞共同考妣對
CREE
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動越似在其中。 之電碗,把已在一九六九年九月開辦一項有關 近年制上游操作科普雷文强飓程之新,其:
一盤仔街坊會學校 定期舉行開幕禮
指利會,爲當納區內 《霸燈社》阿仔街
·岸沿動系起見在利臣
ATS-MONE!
«.g. dilution, solution,
(notes there ATO KING ZURt changes zavolvang unly physical shanges of stater latent heat of fusion latent haat af vaporination).
Les the tribasio organio acid to be denoted
the formula R(COOH), • Thus the silver salt
be represented by the formula poriado
"Veight of silver salt u
in the
17.854 8. 16.520 = 1,334
During ignition, the acid radical part was completely oxidinadı
R(000′′)3(48*
20
Carbon dioxide + Stean + 34g
Meigat of silver remaining in ormelnie in
- 16.520 BM.
0.841 17.361 ge Therefore weight of acid radical part that moskinen with 0.841 ga. silver
1.334
0,841 gm. - 0.493
atomic weight of silver is 107.9 and each. ga-móle of the silver salt contains 3 gn-atomE Z Therefore as-ion weight of the tzibesio noid radical
9.493 + (0.841/3 x 107,9)
0.493 x 3 x 107.9
189.1
0.841
Thus moldeular weight of the tribasio soid
189.7+3 192.T
QUESTIONS FOR NEXT WEEK
1. 2 gas, of oxalio mold which crystallised with
two moleonles of water are heated with oona. B230. What volume of gas is formed at 13°C and 570 mm.2
If this gas were allowed to stand over potaski what volume of ram would remain at X-TAP,?
2. What are tas chief physical and chemical ⠀
properties by which motala are distinguished? Illustrate your answer by contrasting a typical metal with a typical non-metal.
Describe WANT IS ODServed and the reactions which occur when the following substances are heatad separately in test tubens (a) load nitrate. (b) prystalline ferrous sulphate, (e) samÓNÍUM nitrate, (4) washing soda, (●) orystalline copper
sulphate.
How is methyl alcohol obtained industrially? Kantion and of its uses. How would you identity a liquid reported to be methyl alcohol? Kow would you detect the presence of ethyl alcohol, in a apecimen of mothyl alcohol?
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