1973-03-15 — Page 27

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1973英文中學會考試題預習專欄

EXAMS MPG 4 AM

化學科(廿一)

Ammonium nitrate NH NO

White deliquescent crystals, soluble in water with absorpt-

ion of heat. Used in manufast- ure of explosives,

Ammonium carbonate (NH) CU

It is unstable and smells strongly of ammonia. This accounts for its use as a contituent of smelling salts.

operties of ammonium salts

When a strong base is added to an ammonium salt and heat is applied, ammonia is produced- 2NaOH

Na2SO + 2H.0 + 2NH

4+

This is good test for ammoni- um salts.

A11 ammonium salts decomposes on heating. Some yield ammopia,

(NU), Co

2NH

and other yield nitrogen or an oxide of nitrogen,

NU NO

Exero1

Part I

10+ 250

1. A mixture of air and ammonia is ignited. Which of the following is. most likely to occur?

A. An explosion forming nitrogen

and water.

A slow burning to farm nitro- gen and water.

An explosion forming an evido of nitrogen and water,

a slow burning forming an oxide of nitrogen and water. Little action unless a catalyst is present.

2. Nitrogen and phosphonous show distinct similarities as non- metals because they both have the

same number of

A. neclear chargea

B. allotropes.

C. oxides

D. hydrides.

E. outer valency electrons

·+3=

2NH+ Heati

In the above reaction, which- or the following sets of condit long will produce the highest percentage yield of ammonia?

A. Low pressure, high temperat-

ure.

B. High pressure, high temperat-

ure.

C. High pressure. low temperat-

ure.

D. Low pressure, low temperature E. Norma" pressure and temperat-

ure.

4. The equation for the catalytic oxidation of ammonia is

A. 4NH2 +502

R. 2NH2

4NH

NH3

20

302

4NO + 6H20 N20+ 3H20

2N

202- >HNO + H2O

E. 2NH. +302

5. The equation

N2+ 3H2

2NH

4H-22 Kcal

NO+3H0

respresents an endothermic reaction.

indicates that a high yield of ammonia can only be obtained if a high temp, is used.

C. indicates that a high yield

of ammonia is only obtain- able if the pressure is low. indicates that a catalyst must be used because of 4,

WAH KIU YAT PO

報6橋

四期星

1913英文中學會考試題預習專欄

volumes of reactants yield only two volumes of products indicates that 11,000 calori es of heat are evolved for. overy mole of ammonia formed,

6. Which of the following 23 847 incorrect statement?

Nitrogen

P. is less soluble than oxygen

in water.

0. has a boiling point higner

than that of oxygen at 1

atmosphere pressure.

R. combines with magnesium to

form magnesium nitride, wher magnesium is burnt in air.

S. 1s a consituent of all living

matter.

is not involved in photosyn thesis.

Ammonia

P. is heavier than air

Q. is an acidic gas

R. is a basic gas

S. is useful in making fertiliz-

er.

can be dried by come.

-ic acid.

When ammonium hydroxide solut- ion is added drop by drop to a solution of zinc sulphate until there is no further reaction, w

an bee that:

P. there is nothing changed. 2. a gelatinous substance is

left.

R. a white precipitate is left. a gelatinous substance is formed and then it disappear a white precipitate is form ed and then it disappears,

One of the following methods shows ammonia containing hydroger

P. It gives white fumes with.

hydrogen chloride.

Q, it is very soluble in water. R. it turns red litmus to blue. S. it reacts with chlorine form

hydrogen chloride.

it reacts with magies.

form mamecium nitride.

10. When ammonium nitrate is heated, the products are:

1. metal

2. metallic oxide

3. oxygen

4. salt

5. nitrogen peroxide

P. 3 and 5

Q.4 and 5.

.R. 2 and 3

S. 3, 4 and 5

I

none of the above

The Tountain experimen often used with ammonia,

A. can not be used with any

other gas.

B. depends upon the alkal nature of the gas..

C. depends upon the increasing solubility of the gas under pressure.

D. depends upon one greav

solubility of the gas in

water.

E. must be carricu vub in

very thin-walled glass fl

و قد حددت بنسبة 11 120

heated cupric oxide. the gases produced are.

1. nitrogen and water A.nitrous oxide and water.

vapour.

C. nitric oxide and water

vapour.

D. nitric oxide and hydrogen. E. nitrous oxide and hydrogen.

13, which compound can be used toI drying the ammonia gas?

4. silica

B. quicklime,

C concentrated sulphuric acid D. calcium chloride

E. phosphorus pentoxide.

14. 40 cm, of dry ammonia gas is passed form a gas syring through a heated tuble and the volume of gas measured in a second gas syr- ing. If the equation for the reactions

2NH

+ 3Н2

Which of the following could be the new volume of gas?

20

B., 40 cm3

C. 60 cm3

cm3

D. 90 cm

E. 160 cm

WAMZAMU

物理科 (廿一)

Physics (21)

Electrostatic generator

Electrophorus

日五十月三年三七九一曆公年二十六国民華中

This is the first simple elect rostatic generator. It consists of an ebonite diso A and a metal plate with an insulating handle H

insulating handla H.

metal plate

ebonite plate

The disc" A 18 rubbed with rur go that it becomes negatively charged The metal plate B is placed of A and its upper face is momentarily touched with a finger

Leaks

Finally the plate B 18 removed by means of the handle H and ite charge is tested with an elect. scope. It will be found that B is positively charged. The charge. on B can be transferred to another conductor C by allowing B to touch 3. B can be brought to touch A again and recharged in the same way. In this way a large charge can be built up on Ca Remarks: (1) In charging the

electrophorus the finger musT. be removed before B is taken away.

(11) Sparas uan ve seen when 18 removed from A. This is due to the work done against the force. of attraction between the opposite charges.

2) Van de Graaff generator

0,000 alts

Shape of E

rubber belt;

pulley driven by motor

The lower pulley is driven by a notor. The rubber belt B runs over the pulleys and near bottom and top of its run, the belt passes lose to the electrodes E which are sharpely pointed combs. Eq is maintained at a potential about. 10,000 volts or more positive with respect to earth so that by the

action at points, the lower par

of the belt receives positive

charge which is then carried uj

into the sphere. By induc

is negatively charged and the

sphere becomes positively charged. The very high negative charge

density at the points of repels electrons in the surrounding air molecules to the belt, thereby discharging the upper part of the belt. The sphere gradually charges up positively until its potential reaches a desirable, value, which depends on the size of the sphere, the potential of E, above earth etc:

Electric field and electric] potential

Consider the situation were a positive charge is moving towards a second charged body which is also positively charged. Suppose the two charges are very far away Then the repulsive force on the moving charge due to the second one is negligibly small. As the first one is approaching the second charged body, the repulsive force on the first one will - becom greater and greater. This repul- sive force is due to the teract

ion of the two charges and ts. called the electric force. Ar electric fold is defined as the region where an electric force. can be detected. An electric fiel can be mapped out by electric field lines. Field lines are always going out from a positive charge and terminate on a negative charge. Field lines never inter- sect with one another. They have the tendency to repel each other. Some simple field line pattems are shown in fig 4.

electric

Lines of forcej

Each point in an elevulle 11ela of a charge is characterized by a quantity called the electric potential. Different points in the same electric field may have. different electric potentials. If they have the same electric potential, they are called equi-◄ potential points. If they lie on a certain surface, then the surface is called an equipotential surface Now consider two points of differ

ent electric potentials, The potential difference (p.d.) be- tween these 2 points is defined as the work done in moving a unit positive charge from the point or higher electric potential to the point of lower electric potential. Thus potential difference may be thought of as being the electric condition which governs the dir ection of flow of electricity from one place to another. It should be remarked that the electric potential of a positively charged body is regarded as posit- ive while that of a negativelv

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