RETOREN
5 APR 1969
WAH KIU YAT PO 報日僑莘
CITY
育教低華頁三第張六第日七十月二年西己屬夏
196999
英文中學會考試題預習
化學科 (廿一)
王錦釗 ®
CHEMISTRY (21)
Consider the following statements ·
I
Air is liquefied by first compressing it, then cooling, and finally expanding it when still
11 Liquid oxygun 19 auricult to solid107 III. Nitrogen obtained from liquid air has a lower
density than that obtained from nitrogenous compounds, owing to the presence of argon in 1 IV Liquid nitrogen boils at a higher temperature
than liquid oxygen, thus making it possible to separate nitrogen from liquid air by fractions】⠀⠀ distillation.
Which of the following alternatives 18 correct? A1 and I only
B
C
II and III only
II and IV only
D I, II and IV only
All four statement i
It is required to prepare a sample of sodium bicarbonate, starting with sodium, Which of the following methods would you use?
Dissolve some sodium in dilute nyarocnsoric acid; then pass carbon dioxide into the solution until it is in excess. Filter off the pracipitate obtained and dry.
Dissolve some sodium in water, and pasa în carovi dioxide into the solution until it is in excess, Filter off the precipitate obtained and dry Dissolve some sodium in dilute hydrochloric acıo then to the resulting solution add a solution of calcium bicarbɔnate. Filter off the precipitate. formed and dry
Dissolve some sodium in water, and pass in carbon dioxide to form the carbonate. Heat the solution to form the bicarbonate. Filter off the precipitate obtained and dry.
Put the metal in a combustion tune, neat and pass carbon dioxide over it.
What impurities are there în carbon dioxide when it
is prepared from marble chips and dilute hydrochlori acid?
A
carbon monoxide, calcium chloride
B hydrogen, water vapour
C hydrogen chloride, water vapour
hydrogen chloride, calcium chloride, water vapour chlorine, calcium chloride
In the fermentation of glucose to alcohol, what percentage of the food value can be considered be 'lost' by conversion into carbon dioxide.
C6H1206 →→→→ 202HOR
B 48.9
5.3 51.1
B 25.6%
200
The most appropriate method of preparing a sampio of anhydrous ferrio chloride, starting with the metal, is tó
A dissolve the metal in dilute hydrochloric acio filter, concentrate by heating, and finally crystallise the salt.
dissolve the metal in dilute hydrochloric acid, pasa in chlorine to oxidise the solution, and the evaporate to dryness.
dissolve the metal in conc. hydrochloric acid, and evaporate to dryness.
dissolve the metal in dilute sulphuric acid, then add sodium chloride solution to precipitate the salt.
pass dry chlorine gas over rea noc Kun wire
30 c.c. of a solution or sulphuric acid can neutralise 15 c.c. of a solution of N NaOH or u of a solution of Na2CO3. The normality of the carbonate solution is
a white precipitate, which dissolves when ther mixture is boiled
E a white precipitate, soluble in dilute nitric
acid
[10, Cupric nitrate crystals may be prepared by
A adding concentrated nitric acid to copper oxide
and heating to red-heat
B adding excess copper to nitric acid, filteri
and crystallising
C adding excess nitric acid to copper, evaporating
to dryness and heating strongly
D neutralising nitric acid with copper sulphate
solution
E double decomposition between copper sulphate and
sodium nitrate
·SOLUTION
I gives in outline the processes involved in the liquefaction of air, Liquid oxygen will be frozen to a pale bluish white solid at -219
B Sodium dissolves in water with a vigorous
reaction. It would not be advisable to dissolv. sodium in hydrochloric acid for the action would be rather violent
2N
20 2No2OH
When carbon dioxide is passed into the resultin solution until it is in execus, sodium bicarbonate will be formed
Sodium bicarbonate is only sparingly soluble in water (100 grams or water will dissolve 9 gms. at 15°C) and will crystallise out of the solutio in the form of small, white crystals.
Both water vapour and hydrochloric acid vapour are collected in the gas jars together with the carbon dioxide,
CHOH
C2H1206
180
of food valus lost
40. X. 180
100%
-100%
180
48.9%
The weight of alcohol obtained is only about half the weight of sugar used to produce it.
Anhydrous ferric chloride cannot be obtained by evaporation of a solution of the compound
3H20 — Fe(OH), 3 HOI
Hydrolysis occurs when the chloride is dissolver in water, and evaporation to dryness will only produce ferric mida,
27(OH)3 Pe203
The anhydrous salt is produced by direct combination of the two elemente
2F 3012
30 d.c. of H2SO solution 15
Mortality of H-501
5.
30
-N2OH
10
solution = 30 cse, ör
HASOL
ties
3C
Normality of Na,CO, solution
20
va pour Pensity
va pour Density of
· ក
20
四期星日三月四年九六九一醫公年八十五國民華中
(揲第六張第二頁)
文中學會考試題預習
物理科 (廿二 )
·陸永熾
x.6
1otal external resistance R
ohms.
Current in circuit I
12
5
amp.
But only of the total current passes through the 9-ohm resistance, of it shurts through the 6-ohm resistor,
Therefore the current in 9-ohm resistance is
2x 20 amp.
7
The voltmeter reading:
9- 10
volta.
The current in the 9-ohm resistance is 1 amp., the voltmeter reading is then 102 volts.
(2 ahms
(1) The resistance between B
BC
4 x 12 +12
- 3 chis
11 The current at C is the same as at A which
is 48mp.
(111) Voltage drop between A and B
4 x 2 - 8 volts'
B-3N/2L
CM/S
D 20/5 KN/2
7. & gas mixture contains 5 ml. 1, 5 ml. CH, and
5 ml. Co. Its vapour density
A 2.6
B. 5.2
07.67
D. 13.0
E 15.34
ViLute sulphuric acid may be distinguished from dilute hydrochloric acid by adding
A sugar, which turns black in sulphuric acid :
B barium chloride solution, which causes only.
sulphuric acid to form a white precipitate lead nitrate solution, which causes only sulphuric acid to form a white precipitats sodium sulphite, which causes only sulphuric acid to produce a choking gas a
manganese dioxide, which causes only hydrochloric acid to produce a gas, which bleaches red litmus
A white pander r dissolves in water and produces a blue solution. After acidifying the solution with hydrochloric acid, barium chloride is added and a white precipitate appears in the blue solution. I lead nitrate solution is added to a solution of P in water, there is
·A a brown gas given off
a white precipitate
Ga white precipitate, insoluble when the mixture
is boile
10:
Papour Dry of 00
<5: 8x5 14x5
Vapour Versity
tre Mixturė
23
7.6%
8 Dilute sulphuric has no action on sugar
Dilute hydrochloric acid is not reacted upon by manganese dioxid
Both dilute acids react with lead nitrate to form white precipitates and with sodium sulphite to yield sulphur dioxide
L2SO, BaCl," BaSO⚫ 2801
P is apparently anhydrous copper sulphate. Anhydrous copper sulphate (a white solid) dissolv
in water to give a blue solution.
BaCl, Baso + CuCl
white ppt.
Lead nitrate solution added to a solution of:) in water will produce a white precipitate, Insoluble even when the mixture is boiled.
CuSOP
Pu(NO3)2 Pos • Cu(NO
Copper nitrate crystals are obtained by crystallisation from copper nitrate solution
30u • 8HNO, - 30u(NO3)2 • 2ND LH2O Cu(NO3)2 + 380 • Cu(NO3)2 $3,0
+
(iv) The current in the main circuit branches out
into 1 and I passing through the - and 12- ont resistors respectively,
12124 - 3:1
Therefore, the current in the 4-ohm resistof is 3 amperes
Questions for next week
43. (a) What is:
(1) the positive pole;
(ii) the negative pole;
(iii) the electrolyte; and
(iv) the source of energy, in a simple call?
(b) When a simple call ia connected to a small light
bulb, the light goes out in a short time.
(1) What element causes this?
(11) On what pole is it formed?
(111) Draw a diagram of the simple cell while
it is working, showing what happens inside, and give two reasons why it stops working. Draw a diagram, suitably labelled, of a dry cell, and briefly describe the action inside the cell when it is working. What advantage has a dry cell over the wet type? What are the factors which affect the internal resistance of the dry cell?
44. (a) Name two advantages of an accumulator over a
primary cell,
(b) What 19:
(1) The positive pole;
(11) The negative polo;
(111) The electrolyte,
in an acid-type accumulator? in an alkaline-type accumulator?:)
(c) What happens to the em, and to the acid when
lead acid accumulator
(1) used;
(ii) re-charged?
(d) Praw a circuit showing now two accumlators are re-charged from a main supply, and explain why: (1)a D.C. supply is needed
(11) a resistor must be included.
(e) What harmful effect is produced when a lead-acid
accumulator continues to be used without continual re-charging?
Explain how t
(1) a hydrometer; (ii) grease, (iii) a voltmeter; (iv) distilled water are all useful. in the care of an accumulator.
(f) Six accumulators, each of auf. 19 volts, are
placed in series and recharged from a D.C. supply of 100 volts. The charging current needed] 18 4 amp, Neglecting the internal resistance of the accumulatora, calculate the extrą resistance needed.