1968-12-04 — Page 22

實二第張六第 日五十月十年申戊

WAH KIU YAT PO

育僑華

敎

7969

文中學會考試題預習

物理科

(五)

陸永熾、

PHYSICS (5)

The State of Patter

SOLID STATE. A substance in the gassona stata hɛ its molecules relatively far apart. The molecules are moving at randon and the average speed is high. They collide one another continuously and push their neighbouring molecules so far apart that the existing attraction force is negligible In this state, the substanne has neither definite shape nor a definite volume,

LIQUID STATE. If a substance in the gaseous state is cooled, that is losing energy, and so has its molecules slowed down, the collisions are less violent. The molecules do not then move. in as far towards each other, so they do not experience such large repelling forces, and do bat move out so far apart. They keep within a range by an attraction force. In such a state, A definite volum is maintained but it fails to have a definite shape. A liquid shapes itself as its container:

SOLID STATE. When a liquid has energy taken from it, the vibrations of its molecules becomes less violent until the molecules lock into position ition in a regular arrangement, still vibrating, but in a fixed position. The substance is then in a solid state. Unlike the liquid and gaseous state,

solid has definite shape and volume. The shape of a particular solid in the crystallins form, and its resistance to change of shape, depend un the way in which the molecules lock together.

If the solid is further cooled, the vibracions of molecules become slower and slower.

SURFACE TENSION

The molecules in a liquid rave attracting and repelling forces exerted on than by other molécules from all sides. Those bear the surface have more molecules influencing them from attracting forces would pull then back.

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·本星期日下午請將盧氏主講

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上文中學會考試題預習

1969

化學科

(四)

CHEMISTRY: Zas.

王錦釗

Carbon dioxide is prepared in the laboratory by the action of dilute hydrochloric acid on marble chips. The gas so obtained contains acid spray and water. vapour as impurities. If the gas is required in a purs, dry state, it is first passed through a second Drechsel bottle containing water to remove acid spray and then through a second Drechsel bottle containing concentrated sulphuric acid to remove the water. vapour. The gas is then collected by downward delivery.

Calcium

ZHG1

hydrochlorin salefum Carbon carbonate acid.

chloride dioixde

Pure dry

CO2

When,

carbon dioxide is

passed

for a longer,

period of time, the milky solution becomes clear

again because calcium bicarbonate, which is a soluble substance is formed,

Caço

calcium bicarbonato.

To prepare a sample of sodium bicarbonate in the laboratory,

A solution of sodium hydroxide ja saturated with carbon dioxide, when a solution of sodium bicarbonate will be formed."

NaOH

NaHCO3

The solution is allowed to evaporate as room temperature, when crystals of sodium bicarbonate are formed, These crystals can be filtered off and dried?

Dilute hydrochloric

acid.

(To dry the gas)

(a) When carbon dioxide is passed over red hot coka,

it is reduced to carbon monoxide.

coke (red hot)

200. carbon. monozide

(b) To prepare a simple of sodium bicarbonate in

the laboratory.

A solution of sodium nyuroxide is again Baturated with carbon dioxide until all the alkali is converted into a solution of sodium bicarbonate. An equal volume of the originel Caustic soda solution is added to the bicarbonate solution, forming a solution of sodium carbonate.

N&CH - Na2CO3 • H2O

The solution is evaporated down and allowed, to cool, Crystals of sodium carbonate are formed which can be filtered off and dried.

In the solvay Process, for the manufacture of godium carbonate, the raw materials, salt and lame stone, are indirectly converted into sodium carbonate and calcium chloride. The process deperds upon the fact that sodium bicarbonata is only slightly soluble in water, and may be considered to ha insoluble in brine,

In practice brines

with aqumonia gas

and carbon dioxide is bubbled through the solution.

MC1:+

NH3

• NH 011, ..., (1)

The sodium bicarbonate de precipitated and separated from the mixture by filtration, and sodium carbonate is then obtained by igniting. sodium bicarbonate obtained.

2NaHCO3 • Na2CO3 + H2O

CO2

The limestone is heated in kiina to produce carbon dioxide and quicklime.

water

(To remove

Bold spray)

Cone, H250

Molecule à is in the imverig of the liquid. All the molecules that have an appreciable attraction on A are those contained in a sphere of centre A. Resultant force on A în any direction is saro, Molecules B and C are on the surface. The spheres of the same radius are drawn with B and C a centres, Half of the sphere is above liquid. Tom horizontal resultant is still tero but the vertical resultants on B and C act towards, the imerior of the liquid.

As a result, the liquid surface tamia to contract and the surface acts like a skin covering the liquid tending to have the surface area minimum. This phenomenon is known as surface tension.

(a) DIFFUSION AND OSMOS IS

The spreading of the molecules of an undisturbed substance into a region which it mae not hitherto occupied, or into another substance of less dense is known as diffusion, This can be explained by the Brownian movement of molecules. Diffusion occurs in solid liquid and gaseous states.

If solution is separated from some of the pure solvent by a semi-permeable membrana which permits passage of the solvent but not the solute, and effect call osmosis occurs.

Moment or force

The moment of foras about a point is the turning effect of the færres, it is measured by the product of the force and the perpendicular dis'ance of its line of action from the point. (b) Centre of gravity

The pulls of the Barth exerting on different parts of a body have a resultant whichĮ passes through a point. The resultant force is called the weight. The point of application of the resultant is called the centre of gravity. (c) The wire frans is

erected vertically as

in fig. AN

The forces acting

down the vertical frames are equal, both being 15 lb.wt. Therefore the centre of gravity of whole frame work lies an AAC

(b) When a piece or burning magnesium ribben is

lowered into a gas jar of carbon dioxide, it continues to burn with some difficulty. The products of the reaction are magnesium oxide, a white solid, which will be obtained at the bottom of the gas jar, and specks of carbon,

which will be seen on the sides of the gas

208.

2Mg0 magnesium Carbon oxide

When carbon dioxide is bubbled into a test tube containing lime water, an insoluble suspension of insoluble calcium carbonate is formed, which gives the solution a milky appearance.

∙Ca(CH),

1ime water

Ca CO2 calcium carbonate

The wire frame 18 put se in fig. 8.

As the weights on both sides are in ratio

of 31, the G.G. lies on BB cutting the frame

into ratio 1 to 3, that is ft to 13 ft.

The G.G. is on the intersection of AA and BB. That is 1 ft. from the 3 - 12 era and 13 ft. from the 3 - 6 arm.

Question for this week

9. (a) What is meant by the law of the lever,

Describe the tiree different types of levers and give one example of each kind, showing with the aid of diagrams how the law. ÍR applied and the advantage which it gained. (b) The diagram represents a double-decker ben

CO2

(3)

The carbon dioxide obtained in reactions (2) and (3) is used in reaction (1).

The quicklime is slaked to form slake I ime;

Ca O

•[Ca(OH)2.

which is heated together with the ammonium chloride obtained from reaction (1) to produce. ammonia,

2NH, C1 • Ca(OH)2 CaCl2 23 -2H-0

Thus, after the original change of ammonia, no other materials are needed, except for salt and lineatone.

Questions for next week (6)

Next Wednesday, we will attempt a number of multiple choice questions on Hardness of water, sosp and detergents, carbon monoxide and gaseous fuels.

under test for stability. The distance between the outside edges of its wheel is 2.45 metres and the angle of tilt when it begins to topple is 30° from the vertical. Find (1) tre height of G.G. of the bus, (11) the horizontal force which, applied through C,G. weźll Just bold the bus in position when leaning at an angle or 45°. (weight of bus - 8000 kr.t.)

10. (a) Under what condition will

(1) three forces (not parallel). (11) three forces (parallel)

be in equilibrium?

(h) Describe an experiment to verify the law you}

use in (a/i).

(c) A rectangular picture frame 16 in. vide ia suspended from a nail by a cord 3 ft. long wbose two ends are attached to the two top corners of the frame. Calculate the tension in the cord if the mäss of the frame is 5 lb.