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The alkali metals may be prepared from
the molten their compounds by electrolysis in etate or by reduction by carbon at high temperatures or even by reduction by less
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1770英文中學會考試題預習專欄
化學科
人書院主編
CHEMISTRY (10)
SOLUTIONS FOR LAST WEEK
(+)
1. From experimental determination 1 gm. of lead
yielded 1.077 gm. lead oxide and 1.154 gm. lead eulphide respectively.
Thus for 1 go. of lead sulphide, amount of sulphur
0.154
16 1 X
1.154 m. 0.1334 gm.
amount of load oxide that contain the same quantity of lead as in 1 gai, lead sulphids
X
1.077 1.154
g. - 0.9332 gm.
aasuming that the lead sulphate obtained by nitric acid oxidation of lead sulphide is the same as that would be produced for a reaction of lead oxide with Bulphuric acid anhydride, then
The amount of sulphuric acid anhydride in 1.268 gm. of lead sulphate
(1.268 0.9332) gm、
-0.3348.ga,
Since to 0.1348 gm. of the anhydride 0.1334 gm. of Sulphur 18 present
Therefore percentage compositions
LA the anhydride
are
0.334
for eulphur •
0 3348
* .00% 39.85%
60.15%
ror oxygen • (100 · 19.85) %.
Ao has been pointed out above, the assumption taken in the calculation 18 that there 19 00 change in valency of lead in the sulphide, oxide or sulphate. This may be affirmed by taking sons lead oxide, dissolving it in hydrochloric acid, allowing the resulting solution to react with Bulphuric acid The lead sulphate obtained in this case 18 to de compared with that obtained through oxidation of the Bulphide.
2, in each of tere three states Ot matter--gaseous,
liquid and solid--there is some distance between the molecules or atose that comprise a given Bubstance. Consequently the molecules or atoma of one subatanoo may be able to fit themselves into the spaces between the atome oc molecules of another substance that 18, one e ubstance may be dispersed throughout another substance. The system that results from this dispersion of aube tancer is called a solution of the two Bube tanoGS.
Furthermore, A Grus 80 Lution must be one in which the components ara ia a state of homogenous molecular dispersion, but without chemical binding for otherwise the combination would produce a compound rather than a solution.
If a solute is added to a polvent and the mixture stirred, the crystale first disappeare, 1.8. dissolves. However, if additional amounts of solute is continuously added, there will eventually be a situation when the added crystals simply fall to the bottom and fail to dissolve. Apparently the solute in solution has reached its maximum possible concentration for the particular temperature. The solution is now saturated with respect to the aolute, and the solid solute in contact with the solution in in equilibrium with the solute in solution.
Thus in defining the term 'saturated solution' the key word is equilibrium. A saturated solution la one in which an equilibrium exists between the solid solute and the solute in solution. Or, the process of dissolution occurs at the same rate the procese of crystallization.
ag
If the adding of solute is stopped before the maximum (equlibrian) concentration was reached, the resulting solution is unsaturated. The amount of solute present may vary from mare trace to a concentration just less than that of a saturated Bolution. As there is no excess supply of1solid Dolute in contact with the solution, equilibrium cannot be established.
A solution that contains more solute than 18 present in an equilibrium solution under similar experimental conditions is called a supersaturated solution. Buch a solution cannot exist if any undissolved solute is present. Consequently, supersaturated solutions are not in equilibrium with any excess solid. A supersaturated solution
electropositive metals such as Ca, Al, and Mg. Thus sodium metal may be prepared by electrol- ysis of fused sodium hydroxide:
at cathode Na
at anodo он - OH - e: 40H -
中文中學會考試題預専裸
王淑方・
7-1-69
英文科 (十)
2H20.021
(B)
THE ARTICLES
iron bath
The sodium hydroxide 10 melted in an by gas burners, the cathode 18 made of steel, and the anode made of nickel to resist
· oxidation,
(b) Sodium nitrate
trested
A solution of sodium hydroxide 18 with sufficient nitric acid, boiled to evaporate a majority of water and allowed to cool, sodium nitrate will crystallize out. As sodium nitrate is very soluble in water, the starting solutions must be of a fairly high concentration.
NaOH +
HNO2 = NaNO3
(c) Sodium carbonate
sciution
Sodium hydroxide 18 added to a or ammonium carbonate and boiled. Ammonia is displaced by the sodium and is driven off. Evaporation of the solution to saturation and cooling yields sodium carbonate
2NaOH +
+
(NH4)2CO3 - Na2CO3 2NH3
(d) Sodium bicarbonate
2H20
To a cold concentrated solution of sodium carbonate prepared by the method in (c), carbon dioxide is bubbled. Since sodiun bicarbonate is not particularly soluble in water, it separates out as white crystals:
Na2CO3 + CO2 + H2O - 2NaнCO2↓
(e) Sodium bisulphate
This salt can be prepared in the laboratory by mixing solutions of sodium hydroxide end dilute sulphuric acid, and evaporating to crystallizing point. With two equivalente of acid to one of base. bisulphate 18 obtained:
NaOH +
= NaUSO
4
the
4-(a) Chlorine reacte with ammonia by replacement of
the hydrogens:
Thus in presence of excess chlorine, hydroger chloride and nitrogen trichloride are formed:
+
3018
=
NCI 3
+
H20
NH408
3HC1 +
However, in the presence of excess ammonia, the nitrogen trichloride le decomposed:
NHOF NO3 - N2
3H01 -
So that the over all reaction 191
૬
301, + 8NH OH - N2
+ NHC1
BH2O
(b) Chlorine combines directly with tin to form
stannic chloride, however the reaction 18 catalysed by a trace of water.
Sn + 2012
=
SnCl4
3 Tim
(c) Aluminium is a strongly reducing metal,
combines very vigorously with chlorine yielding the chloride?:
2A 1 7
3012
24101
a) if chlorias is passed into an aqueous solution
of subphur dioxide, 1.6. sulphurous acid, Bulphuric and hydrochloric acids are formed:
C12
乖
28,0 - 8,504 2HC1
(e) Carbon monocide will unite with chlorine, in Bunlight ar ሳ presence of heated animal cbercoal to fora sarbonyl chloride, cocl2 19100 kDown sa phosgene). This may be considered ME D addition reaction •
CC
Cl2
COOL 2
QUESTIONS FOR NEXT WEEK
4.
is similar to an unsaturated solution, in that neither is at equilibrium.
The solubility of potassium nitrate in water at 15°C may be determined as follows: A saturated, solution of the solid is first prepared, either by stirring an excess of the solid with the solvent for about an hour in a thermostat, or by heating to obtain a nearly saturated solution at a higher temperature and then cooling down in the presence of excess of solid. A given weight of the saturated solution is then taken, and the quantity of solute determined by evaporating to drynase on a water bath. The solubility may be expressed in grams of dissolved solute per 100 grams of water.
3. (a) Metallic sodium
of
Wrɔta op account of the preparation, properties andreactione the oxides of aitrogen.
write down and namə the structural isomers of
DolBowl OT formule Cla Write the chemical
A compound
equation for much of INGSA when they react with bolling aquaque sodium hydroxide solution
Name the type of companad produced in egob reaction
moleculo! formula C decoldwizes
bromine solution and CL10 permanganate solution and dissolves in concentrated sulphuric
treatment wat byar ogso platinum ostalyst, 11 1 Deduce the fordule of 196 reactione Involved In the proceduræð mentioned
When a mixture of
(1)
LESSON TEN
CHAPTER THQ
GENERAL ENGLISH.
The Demonstrative Adjectives a* ('an') and
'the' are usually called Articles.
Indefinite Article
'A' ('An') .s called the Indefinite Article because if leaves indefinite the person or thing
spoken of.
2.2. a boy
a boat
a book
f
any boy
any boat
any book
lat is used before a word beginning with a consonant sound. e.g. a girl, a man,
NOTE:
a snip,
a book
When words begin with a consonant sound of "yu*, we also use the Article 'a'
a university. a European,
a union,
a useful article.
*An' is used before word beginning with
a vowel sound,
e.a
NOTE:
with
eig.
An orange,
an apple;
an island, an hour.
an honest man,
an enemy
an herr,
an umbrella.
The words 'hour, 'honest ' and 'heir'i
begin with a vowel sound,
as the inftial
consonant、 "h" is not pronounced.
"An' is also used before words beginning "h' and not accented on the first syllabl
An hotel, an historical novel
(11) Definite Article
The is called the Definite Article for
It points out some particular person or thing spoken of.
c.e
She sent for the doctor.
Lee.
He put
some particular doctor a pencil on the table, f.e. some particular table.
THE USE OF THE INDEFINITE ARTICLE
The Indefinite article is used only before singulaḥ countable nouns.
e.g. a book, 2 year & child.
(a)
·e.gi
With the meaning of one, 'any'
He gave me a for
(b)
(C)
I have a brother
In certain expressions of measurement;
E.2.
He likes to drive his car at sixty miles
an hour?
sne goes to school three times a week. He sells the butter at 5s. a pound.
Before dozen, hundred, thousand, million: e.2. She gave me a dozen eggs.
A hundred goats were in the plain.
Before singular predicative nouns denoting profession, trade, religion, class, etc.
My brother wants to be a teacher
John's sister
is an accountant
If the noun denotes a title or office that can only be held by ope person at a time The indefinite article is not used.
They elected him President of the
Geography Society
(not _'a president"}
(d)
2.2.
NOTE;
(e)
The Indefinite Article 15 also used to refer to a person known only as a name. 2.2.
"A Mr. Smith rang you up this morning.
When you were out," Jack told Jim,
(The 'A' gives the meaning:
Jack has no idea who he is, but he just told Jack that his name dr. Smith.)
was
(f) With the meaning 'same" in certain expressJONSI 4.2. The two dresses wore much of a size.
(1.0. The two dresses were of tử
same size.}
(g)
Before a noun in apposition when the thing or person is assumed not to be familiar.
Jill Smith, a housefe in Lancashire
it yesterday.
was hurt in an aco
(h)
In exclamatory sentences
routed 0. What
there the noun as singular and countable
*. £. What a pretty girl vo
What a clever boy ne
ANSWERS TO EXERCISE 10
On
Ine presence of a convertoa to 1-butane
compound and exploit
i he
(1)
asked my brother
luberner) Y
4. Nh
20
with him,
(2)
The hunter asked someone seed a wounded hare
(3)
He asked if (whether) Kelly England
da 20142 Yo
121
Inorganic Bobetances,
with+
B
was
。
B was heated together
concentrated output e acid, a greenish-yellow gas wab evolved. black power, ansoluble AD water or dilute acids It dissolved an not, concentrated sulphuric acid, giving off a colourless gas which supported combustion; and in hot concentrated hydrochloric acid; evolving the 6ame 38 as when heated together with B and concentrated sulphuric pola. B was
in the form of a whate deliquescent solid, which turn to a white muca on heating. A solution of B in hydrochloric acid did not react with hydrogen sulphide; however it gives a white precipitate with ammonium hydroxide which dissolves in exceso, if hydrogen sulphide is again passed, a whatish precipitate is formed.
Deduce the natures of A and B, and explain the above observations.
wherner i
ndo
lach fakeo JORD + twhether i 1par nad (ed The
dogs before Sunser
(S)
HE (Sné, etc I said wit
that
me
101
channer. etc.) ne could goe ing ha ДЕП
and asked (whether) 1 could tend him sae. Edward asked his mother . (whether) frut Tha( Eday was Teavana Hong Kon tor Americo.
was
(81
Me (She, etc.) asked me it (whether) they had all gone Co The party last night.
Jill asked me (him, her, etc.) where ann had 39f haar cut..
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