1975-11-13 — Page 19

刊特節朗青溆 旟三第張五第 日一十月十年卯乙歷 WAH KIU YAT PO

報日僑華

0903 中學會考試題預習專欄

化學科 (-) 李國榮。

四期星

1) Glucose and common salt.

(5 points) (2) Ethane and ethene. (5 points) Question 5

日三十月一十年五七九一歷公年四十六國民春中

CHEMISTRY (1)

zu mol gês at S.T.P. occupies

22.4 liters.

Mg 24

C135.5:

Na = 23

Ag = 108

Answer 3 questions only

Question 1

a. When a ribbon of magnesium metal

was added to a colourless liquid W, a gas was evolved. Some of this liquid W was reacted with phosphor- us pentachloride, and hydrogen chloride vapour was observed. The liquid W was found to have a mole- cular formula C2H402. Using the above informations, try to answer the following questions.

(1) What is the probable structural

formula for W? Explain your answer. (9 points)

(2) What would be its reaction with

sodium hydroxide? (Equation is required) (4 points)

(3) Give one reaction from which W

can be produced in the laboratory? (Equation is required) (4 points) b. What isomers are probably existing

in pentane (CH2)? Write their structural formulae and name them.

(8 points)

Question 2

An unknown I was a colourless Orystal. A student obtained some. solid of Y and he prepared a solutior fof it. When he added calcium chlor

ide solution to the solution of Y he obtained a white precipitate.

He collected some of this precipi- tate and heated it. He observed the evolution of a colourless gas,

and white residue was left behind.

a

When he heated the solid of Y he Liid not observe any changes at all.

But when he added dilute hydrochloric Facid to Y, he obtained the same

colourless gas, and a colourless solution resulted.

He found the gas to be faintly acidic, and was unable to turn litmus-paper to become completely

red.

Now try to answer these questions. (1) Which of the following catione

may be contained in Y?

(1) Na11 (ii) K11 (iii) Cu+2 (iv) NH4-**

+1 (v) He+

Explain your answer (5 points) 2) Which of the following anions.

may be convained in Y?

(1) 01 (ii) Br1 (iii) S)

-1

(iv) HCO3 (v) CO3-

Explain your answer (5 points)

How could he further identify the navure of the probable anion? (Equations are required.)

(5 points)

(4) What probably was the white

precipitate he obtained?

Give an

Ionic equation for the possible reaction.

(5 points)

(5) What probably was the gas?

Explain your answer. (5 points) Question 3

a-Gas jar A was connected to the tap, and all of the gas jars were of the Same volume, Relatively pure nitric oxide was contained in jar B and oxygen was contained in jar C. connection between jar B and C was controlled by a clip S, which was put in place before the experiment atarted.

The

All volumes measured in this experiment were at the same temper- ature and pressure.

connected to

tap

Water

rubber tubing

brothen

JAK AN

JAR B JAR C DIAGRAM FOR QUESTION

(1) What could be observed in jar 0

if the tap was turned on and the clip S was removed at the same time? Give an equation for the possible reaction. (5 points)

(2) After a while, would water enter jar C? If so, what would be the approximate volume remaining un- filled by the entering water? Explain.

(5 points).

(3) Would the water entering jar C

react with anything at all? Give an equation for the possible reaction if your answer is yes.

(5 points)

b. Explain the following observat-

ions by giving an equation for each case.

(1) When chlorine gas is bubbled

through acidified sodium bromide solution, the solution turns to a red colour. (5 points) (2) When a fresh solution of chlorine

was placed under sunlight, a colourless gas can be collected.

(5 points)

Question 4

a. Explain the following statements.

Equations are required unless otherwise specified.

(1) Sulfuric acid is added to hydro-

gen peroxide solution. (No equat→ ions required.) (2 points) (2) Sulfuric acid is used in the

esterification of an alkanoic acid and an alcohol. (No equations required)

(3 points)

(3) Sulfuric acid is used instead of water in Contact Process to disso- lve sulfur trioxide, (4 points) (4) Sulfuric acid is used in the

production of carbon monoxide. from formic acid.

(4 points)

(5) Sulfuric acid is seldom weighed out by means of a beam balance. (No equations required) (2 points).

b. In each case give he chemical

method by which you can distinguish between the pair of compounds. Equations are required.

500 ml of hydrochloric acid was used to dissolve 12 gm of magnesium metal. The resultant solution re- quired 100 ml of a one molar sodium hydroxide solution to exactly neutr- alise it.

(1) What was the amount of hydrochl

oric acid (in gm mol) reacted with sodium hydroxide? (5 points) (2) What was the amount of hydrochl- oric acid (in gm mol) reacted with magnesium?

(5 points) (3) What was the molarity of the

original hydrochloric solution?

(5 points) (4) What was the molarity of the

final sodium chloride solution?

(5 points) (5) If a 0.05 Molar solution of

silver nitrate was added to the final solution. What would be the weight of silver chloride obtain-c ed? (Assuming complete reaction)

(5 points)

物理科

PHYSICS

(---)

·(1)

何輝明

This column is carefully

designed to suit the Physics

syllabus of H.K.C.E.E. but it is not intended to be an instant miraculous help for lazy students, it aims to encourage them in their over-all revision and to develop the ability of solving various type of problems.

A series of conventional test- papers are set up for rehearsal purpose, with answers given in the following weeks. We hope that students can reinforce their under standing through these papers.

18.

The ship A is steaming due sast at 30 km/hr. and the other ship B due south 40 km/hr. Find the velocity of B when observed by a observer standing on A. b..(1) Find the

centre of gravity of the thin uniform plate and state its "position as perpen-

dicular distance from AB and BC.

B

8cm-

(ii) If the mass per unit area of the plate is 1.5 g/cm2, and the plate is suspended freely from B, what. is the magnitude of the horizontal force F, which, when applied at pt. F, will keep the side AB vertically?

(iii) If the plate is suspended freely at B, find the angle of the side AB makes with a plumb-line also hung from 3.

c. The following observations were

made with a simple pendulum con-

sisting of a length of string andi

a spherical hob.

Length of pendulum (m) Time for 50

oscillations.

(8)

0.2 0.4 0.6 0.8 1.0

45 63.5 77.5 90 100

(1) Draw a diagram to show the set-up of the apparatus and indi- cate the effective length of the pendulum.

(ii) Using diagram to show what is meant by one completer oscilla- tion.

(iii) How would the period of the pendulum be affected if the masa of the bob were doubled,

(iv) Plot a graph of T2(period) against the length of pendulum 1.

(v) Calculate the value of g in this experiment.

2a. Two pieces of clean capillary

tube are placed uprihgt, one in a beaker of mercury and the other in a beaker of water: Each tube is pushed well down, raised a little. and then clamped.

(i) Draw sketches to show the liquid surfaces inside and outside the tubes.

(ii) Give a short explanation of these effects in terms of the forces between molecules.

b. (1) Using simple diagrams, show

how you would set up a simple barometer and indicate how to: measure the atmospheric pressure. (ii) What are the objections to the use of water as the barometric liquid?

c. A faulty barometer contains a little air and the tube standa 900 mm above the mercury in the reservoir. On a certain day it reads 650 mm Hg. On being tilted the vertical height of the mercury becomes 625 mm while the space above it is now 200 mm long.

(i) Calculate the pressure p1 in mm of Hg, of the air in the space of figure 1.

(ii) What is the atmospheric pressure, F.2 in mm Hg, when the above observations were made?

figure

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