1975-12-25 — Page 22

真二第張六第 日三廿月一十年卯乙

1976中學會考試題預習專欄

堅道書院主編

化學科

(七)

李國榮

CHEMISTRY (7)

G RAM MOLECULAR VOLUME = 22.4 liters

at S.T.P.

K=

1A.

39, 0 = 16, H = 1

Hent

Hear

water

chips

iron filing

·Water

Water is boiled in test tube A and steam passes through glass tube B which contains a porcelain boat filled with iron filing. A colorless gas X is then collected in gas jar Cover water.

報日僑華

WAH KIU YAT PO

B. How can the following preparat-

ions be achieved? Give equations.

(i) sodium hydroxide from sodium.

carbonate.

(ii) sodium sulfide from sodium

hydroxide.

(iii) ferrous chloride from iron.

C. How can you prove the presence

of the mentioned element(s) in each of the following compounds. Give appropriate equations.

(i) Bromine in sodium bromide. (ii) Hydrogen and chlorine in hy-

drogen chloride.

(iii) Nitrogen in nitrous oxide.

(iv):Oxygen in nitric acid.

3A. With the help of equations,

explain the following:-

(9)

(i) When ammonium nitrate is heated no solid residue or product can be obtained.

(ii) When sodium hydroxide solution

is added to a solution of zinc nitrate, a white precipitate is

四期星

日五廿月二十年五七九一靨公年四十六國民輋中目播育教

the wt. of water having the same

(ii) Potassium chlorate is heated to

produce oxygen, which is then

verified by applying a glowing

I splinter. into the test-tube.

formed first, but it redissolves of on further addition of the alkali,

(6).

B. Tell, with the help of equations. how the following preparations be achieved:-

(i) Metallic sodium from sodium

hydroxide.

(ii) Bthene from ethyl alcohol.

(8) C. Whén a dark colored solid is. treated with dilute hydrochloric acid a colorless gas of pungent smell is evolved. When this gas is passed into a solution of potassium dichromate solution, the solution tums green and a yellow precipitate is formed. When a solution of lead nitrate is used instead, a black. precipitate is observed. (1) Give an equation to show the

reaciton of the gas evolved with. lead nitrate.

(ii) Draw a diagram to show the mole

cular structure of this gas..

(i) What is gas X? Explain with

an equation. (ii) The product in the porcelain

boat is taken out and is gently: heated in a stream of gas X. What F happens? Write an equation. (iii) When X is combusted in air,

colorless liquid can be seen to condense on a cold surface. What is this liquid? Explain。 (7) B. Explain the following observat- cions with the help of equations.

(i) Bleaching powder when exposed

in air smells of chlorine. (ii) When a small piece of sodium

metal is added to ethyl alcohol al colorless gas is evolved. (iii) When a buming piece of mag nesium metal is lowered into a gas jar of carbon dioxide, the metal continues to bum and black specks are form on sides of the (8) jar.. C. 24m or a monobasic acid requir- -1% of wa

ed 26ml of a solution of potassium | 44. hydroxide for exact neutralization The strength of the potassium hyt droxide solution was found to be 14gm/liter. 100ml af the acid was then used to produce hydrogen gas by reacting it with. zinc metal. Assuming all acid was completely used up, what would be the volume: of hydrogen evolved at 750mm and

(10) 17902

2A.

Copper Strip

Colorless yus

Ancele

platnum

"Sopper (-4). sulfate Selation

The figure shows the apparatus. used in an experiment for the effects brought about by an elec- tric current on a solution of. copper (TI) sulfate, A colorless

gas was seen to be collected in the test-tube over the anode. The cathode was later found to have increased in mass. (i) What kind of ions are in the solution? How did they migrate when the circuit was closed? (ii) What happened at the cathode?

Write an ionic equation... (iii) What happened at the anode?

Write an ionic equation. (iv) A the beginning of the experi- ment, the copper (II) sulfate was a Molar solution, how would you expect its concentration to be at the end of the experiment? (8)

(3)

D. How can the following mixtures be separuted -

(1)a mixture of oxygen and nitro-

gen dioxide.

(ii) a sample of 10c.c. ethyl

alcohol containing approximately

tex...

Concentratat

heat

Caterwin

(((3)

Sedivin formats

Wheri code entrated sulfuric acid was added to a flask containing sodium formate a colorless gas was evolved. This gas. passed through. a heated hardglass tube contain- ing a porcelain boat filled with: copper (II) oxide. At the other end of the glass tube a delivery- tube was fitted so that the gas eoming out of the glass-tube would pass through a solution of calcium hydroxide.

(i) Write an equation for the

reaction happened in the flask, Name the products. (ii) After a while, what changes would be observed in the hard glasstube? Give equations. (iii) What changes could be obser

ved in the calcium hydroxide. solution? Give equations. (iv) If calcium oxide had been used

instead of copper (II) oxide, what would have been the obser

vations in (ii) and (iii)? (13)

B. Comment on the following labor~

atory procedures. Give the equat- ions for the reactions.

(i) Zinc powder and dilute hydro-

chloric acid were used to produce hydrogen gas.

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·(4).

C. When nitric oxide is mixed with oxygen the following reaction. happens:-

2NO

+ 02 (5) (g) 02(g)

AH =

2NO.

02(g)

- 27.0 Kcal.

Predict the effect of the following changes in reaction condition on the formation of the gas NO 2

(i) increase in temperature of the.

·reacting mixture.

(ii) increase in pressure of the

reacting mixture.

(iii) increase in the concentration.

of nitric oxide in the reacting mixing without raising the temp- erature.

(8)

a)

f)

物理科

(七)

何輝明

(7)

Physics

and

Saving force or saving time, making the operation convenient are the main purposes to use machines.

Fixed pulley is used to change. the direction of the effort while a movable pulley is used to increase the mechanical advantage.

Method (I) should be chosen since the pulley used is movable, therefore the

volume as that of copper.

upthrust 50 gf

(specific) =

gravity

the spe

of

mass of the substance

mass of water having the

gatelume

50

v) Volume of that piece of copper

400 8

50 cm-

Volume of paraffin displaced when the piece of copper is totally

submerged = 50. co-

(Wt. of paraffin)

displaced

盟

(50) (0.8)

= 40 gf

Apply Archimedes' Principle, the upthrust experienced by copper in paraffin = wt. of paraffin displaced

= 40 sf.

vi) The wt. of that piece of copper in

paraffin 400 - 40 = 360 gr

·vii) Tension in the spring = 360 gf

Apply Hocke's law, the extension produced in the spring =

K

360

= 3.6 cm

the new length)

100

= 50 + 3.6

= 53.6cm

of the spring

Questions for next week

The following data are recorded from an experiment done by a student who aims at finding the specific latent heat of vaporization of water, The heat

the rate of heat supplied is unknown.

Wechanical advantage is improved. source is an electric heater of which.

V.RA of the inclined

(Distance moved by efforty (Distance moved by load)

plane.

AB

1

AC

sin 30

LOAD

A

(i)

The V.R. of the pulley system

is equal to 2.

(A)=(pulley system)

VIR. of the

2 X 24

electric heater

- 50 8

mass of empty glass beaker mass of beaker filled with water= 15g At t=0, temp, of water At-t=231sec, temp. of water At t-557sec,

| The species of the beaker

= 35

65°C

and. with water. = 149 8 Wheat capacity of glasg and v.R.of that of water are 0.84 and 4.2 3/g°C the in- respectively." X

clined plane

a) Suggest one way to minimize the heat

transfer to the surroundings.

(ii) The V.R. of the pulley system b) What is the best starting temperatue

in method (II) is equal to 1.

V.R. of the pulley

(v)=(pia

11tea

1. X 2 2

V.R. of

the in- clined

plane

Since the efficeency for both

n methods is equal to 80%

For method (I), the totalV.R.

*MEA. Efficiency =

VR.

the M.A.Efficiency X (V.R.)

=(80/100) x 4

3.2

For methoa (II), the total V.R.

the M. A. for method (11)

=(80/100) X 2.

1.6

2.1) Apply Hooke's law

Applied force on the spring = 400 gf Extension produced in the spring.

=54 - 50 = 4 co

the spring constant

K =

400 4

=

100 gf/cm

When the piece of copper is totally immersed in water, extension pro- duced in the spring = 53.5 - 50

= 3.5 cm ∴the wt.of that piece of copper

in water = tension in the spring

= (100) (3.5)

350 gf ii) The upthrust exerted by water on

copper = 400 - 350 = 50 gf

.

L

iii) Apply Archimede's Principle,

(weight of the upthrust

\fluid displaced/

完天分分氣分一,短實氣界 辣 0分

so that the rate of heat suplliexi by the electric heater is more accurately measured ?

c) Neglecting the heat transfer to the.

surrounding, calculate the rate

of heat supplied by the electric heater.

d) Determine the mass of water Vaporized

atto557 sec:

e) Find the latent. heat required to

cause such a mass of water to vaporize.

f) Find the specific Tatent heat of. vaporization of water.

g) Sketch. roughly the temp.- time graph

for this experiment,

a)

苏及任一樂氣淨樂卅運、

b)

Distinguish between real expan- sion and apparent expansion of Liquids.

The compensated dilatometer shown in the figure below is used. to measure the real expansion of liquids. Prove that the volume of mercury used is approximately equal to one-seventh of the volume of the bulb.

Coefficient of linear exp. of glass

is 0.000009/°C

Coefficient of expansion of mercury

is 0.00018/°c

故

分

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