1970-01-21 — Page 14

真二第張四第日四十月二十年己

WAH 'KIU YAT PO

郭日僑罩

三期星

日一廿月一年〇七九一靨公年九十五國民耀中 霧教備

K#L/S/128%/$#$#@%$# %%$#*%

#*#*#$

(ë) Solubility of ohiokide a6: 70°C = ́48.3 gm./100gm.

罗僑

water

Fofth $#/4

Solubility, of chloride né 10′′0 - 31.0 gm./100ga.

water

中學入學試試題預習專欄

英文科

智慧出版社出牗

*#$%

#$%$#$%$#$%$#$%$#$%$#8%$#$%$#B%$# %%$#$%$#$%$##$%8#$%$#$%8#G

10英文中學會考試題預習專欄

堅道英文書院主編

化學科

(+3)

OHE ISTAY "(12

SOLUTIONS FOR LAST WEEK.

1. Since percentages of composition by volume of

methane and hydrogen in the mixture ars 30 and 70 rospectively.

22.5 0.0.

Therefore for 75 0.0. or the mixtures Volume of methane (75 x 0.3),0.0. Volume of hydrogen – (15x 0.7) 0.0. – 52.5 0.0. When the mixture is exploded, with oxygen, the following reactions take place:

*

4CH3 + 702-4002 + 620

282 +02- 25,0

According to Avogadro's Xypothesis, equal number of molecules of different gaads oooupy the same volume under the same physical conditions. Thus it should be expaoted that 4 volumes of methane combine with 7 volumes of oxygen to give 4 volumes of osrbon dioxide and 6 volumes of steam; also 2 volumes of hydrogen combine with 1 volume of oxygen goʻ give 2 volumes of a team. However, under the given conditions, the steam would be condensed as wazof, and hence occupying negligible volume,

22.5 6.0. of methane would combine with of oxygen i.s. 39.38 c... and forming of carbon dioxide, i.e. 22.5 c... 52.5 0.0. of hydrogen would combine with

x 22.5 0.0 22.5 c.c,

≈ 52.5 0.0, of oxygen i... 26.25.0.0.

Thus Teslakai volume arter cooling the reaction mixture

(200 39.38 -26.25) + 22.5 0.0. * 156.87 0.0

2. a graph of solubilities of KC1 and KNOT in water!

at different temperatures in construotidi

(*) Temperatura at which both Ka and KFC, posse23,.

the same solubility is 24°ci

(b) Range of temperature at which the chloride is

more soluble than the nitrate is fxam 0′′0 to just bolow 24°C.

(c) Solubility of nitrate at 25°C is 37.5 gm. par 100 gm of water; and at 55°0 is 97.5 g. per 100 ga. of water.

(a) Solubility of nitrats et 70°c

- 138 gm./100 gn.

water

Solability ̋of nitrate at 10°C = 20.9g07/100gm.)

water

Thús if tkara is 100 m. water, weight of, orystals = 117.1 g#.

Actually the saturated solution contains only 30 gm. water, therefore weight of orystal fərmÚČE − 0.3 x 117.1 gm.;= 35.1 gm.

% of this to the total salt originally dissolved.

≈ 100 - 84.8

Thus if there is 100 ga. water, weight of crystals » 17.3 gm.

Actually the saturated solution contains only

30 g, water, therefore weight of coryatal formed -0.3 x 17.3 gm. - 5.2 gm.

f of this to the total salt originally dissolved

17.3

273 x 100 = 36

48.3

Since the percentage yield'of oxystals is much greater in the case of the nitrate, the nitrate is the more suitable salt for this type of crystallization,

(r) At 18°c, the ohloride is more soluble then the nitrate by 5 gm./100 g of water. At 28°C the sitrate is more soluble than the chlorids by 5 gm./100 gm. of water."

(a) In the process of förning a solution of the

salto, i.s, dispersing the particles of a solid,” energy ohanges take place, and heat is usually absorbed. It is for such a reason that the solubilities of most solide increase with ! temperature, as a consequence of Le Chatelier's' principle. is the increase in solubility of potassium chloride with temperature is much less than that of the nitrata, it may be concluded that the heat of solution for the former is mucn Yess than that for the latter.

3. Initially, when carbon dioxide is passed through

limo water, a white precipitate will form owing to the reketion to give the insoluble calcium casbonates

Ca(OH)2 + CO2 = CaCO3 + H2O

However, on prolonged bubbling of carbon dioxide, the insoluble calcium carbonate is furinar converted into the solublə qalòium bicarbonate, so that a clear solution resultat

CaCO3 + CO2 + H2O = Ca(HCO3)2

(a) The resultant mixture of calotum bicarbonate when

treated with soup solution will produce a lather only with difficulty, because there is the eristemos of temporary hardness. The presence of caldina ions in solution, convert soluble ordinary Soaps (sodium palmitate) into an insoluble curd (calcium palmitate) i

2015431.00,ONa + Ca (1003)2 = (C15×31• CD+0}¿C#

++ 2NaHCO2

(b) Whex salcium bicarbonate solution is boiled, it quickly loses carbon dioxide and is coverted back into the insoluble oatsium carbone-ts i

Ca(XG03)2 = CaCO3 + E2O + CO2 ·

(o) When salcium bicarbonate solution is treated

with an equivalent amount of sodium carbonate solution, all the calcium will be precipitated as the insoluble carbonater

Ca(H003), + N82CD3TM- CaCO3 + 2NaHCO3

4. Pyrolusite is a natural ́ore of manganese in the

form of the dioxide. The reactions involved in the fróbles are as followED

Ku2 + 48C1 = MnCl2 + 2H2O + 01,

280 + 3012 - 2FeCl3

The weight of chlorine gas required'in yielding 10 gm, of anhydrous ferric chloride,is ;,

23 x 35.5

{ x 10 gm.1-[6.55°œm)

(55.85 + 3 x 35.5) ||

However, since 10% of chlorine gas generated for the purpose is wasted, originally the sufficient amount of chlorine gad to be generated must basi

10

6.55 x gm.*= 7.28 gm»,

From the first equation, (54193 + 2 x 16) gm. of? pare manganese dioxide would yield (2x35.5) gm. of chlorine gas.

Hence the amount of pure Mno2 required for 7.28 gm.

chlorine

- £85.93

x7.28°gm.

8.91 gm.

As the pyrolusite actually"contains"onlyTM 60% of pure manganese dioxide, the amount of the ore to; be used at the start

SE

10

8.91 x 8.

~ 14.85 gm.

QUESTIONS FOR NEXT WEEK)

1. 50 c.c. of vinegar at 15°C." were put into a 250 ml.

volume trio flask and diluted with de-ionised water to the mark. 50 c.o. of this diluted solution were pipetted for complete neutralization with 0.5M NaOH. 16.9 .o. of the alkali were used.

Assuming that the acidity in vinegar is only'. due to acetic acid, calculate the percentage by weight of this acid in the original vinegar. (Density of vinegar at 15°C is 1.02 gm. per c.c.)

In order to get a correct value for this titration, what indicator is particularly suitable, and why?.

2. What different methods are available for the

preparation of ethylene? Cive reasons for the atructural formula you assign to it,

(+)

SECTION : I 2. E 3. 2

Answers to Frezigun Azazelses

4. G 5. 1

SECTION : II

#

I.

1. that he was going to tea with them that

afternoon.

2. that his horse had won the race the previous

Saturday.

3. if he was hungry.

4. 12 he might go out..

5. if she could go to his house that night.

6. that they had to finish their work before

dinnar.

7. that she had not seen Lucy since the previous

8. not to play on the grasi.

9. to forgive her.

10. to run to the thier.

11. what he could do for her that day. 12. let them go.

13. that it was a lovely puppy.

44. that their but was burat down.

15. that a little boy had been knocked down by

the bus.

SKOTTON A

(multiple choice)

Choose the correct answer by drawing a fimm line

same as the right box.

A. in B. at

A B C D

Example: He is looking C. to

the

D. fox E. on

loat sheep.

A. with B. of

1. I do not agree C. to what they said.

D. on 2. at

A B C D E 1.00000

B. to

A B C D E

2. Leo was playing tricks

people,

C. at D. with E. for

2.

A. by B. to

3. His excuse G. at. being lato was not,

D. about 1. for

ascepted.

ABCDE

A. oz B. about

A B C D E

the 4. ПР

A. The inappeter apaks to us G. in

D. ta E. at

subject of olsaniless-

A. about B. at

5. DDDDD

D. for E. with

a large number of people.

25

5. This poor EAN OWES ROMey C. to

II. Choose the correct word to complete the following

men toneos. Draw a firm line soross the right box.

P. Oh!

4. Husht

Example: 2. Hello? That are you doing

B. Alas!

f. Chi

7. Hurrah!

{there?

Q. Hasily

1. R. Hello? Pon

5. Alka? T. Harrahi

F. Ohi

Q. Hush?

2. R. Halle!

5. Alast

T. Hurraht

{We ̈kave reached the top of

{the mountains)

3. R. Ab!

P Q R S T

RODDE

PQRST

PQ R S T 2. 000E

P. Qă!

Q. Hollo!

PQRST

I had a terrible dram

3. Donan

3. Ales! 7. Good-bye!

last nighte

(未完隸 入第四張第二頁)

3. Describe how you would obtain in the laboratory

pure dry specimenu of

(a) lead monoxide from a mixture of lead monoxide

and cupr10 ox100,

(b) magnesium sulphate crystals from a mixture of

sodium and magnesium sulphates

(c) nitrous oxide from a moiët mixture of nitrous,

and nitric oxides?

Explain, with essential details of experimental procedure, how you would prepars from (a) samonium ohloride, (b) concentrated sulphuric acid, reasonably pura specimens of the elemente contrined in each of these compounds. Three elements are to be` isolated from each compound and the methoår employed are to be auch that the element indubitably come from the starting compound,