1973-04-24 — Page 19

育教偶華 莫三第張五第日二十月三年丑発展夏

1913英文中學會考試題預習專欄

堅道英文問生输

化學科

Solution for last week

Part

2. D

8. R

3

E.

9 R

4. B.

10. S

5. E

11700

12.0.

HADADW

6. S

Metals (2)

(廿七)

Extraction of iron by the blast furnace.

Raw materials: The chief ones are

(1) Haematite Fe 03

(2) Spathic iron ore, Fe00,

(3) Magnetic iron ore Fe204-

The manufacture of pig (or cast) iron

(1) Roasting: The ore is burnt

with a little coal in heaps, or in shallow kilns. Water, carbon dioxide, sulphur, and arsenic are driven off. Spathic ore reacts as follows:

→ 2Fen03 + 4C02↑

4FeCO, + O2

WAH KIU YAT PO

Pig-iron or cast iron:

報日僑事

Pig-iron expands on solidificat -ion. It is very brittle and, is very difficult to weld.. It has low tensile strength because it is impure, contain- ing 3-5 per cent of carbon and 2 per cent of phosphorus, sul- phur, silicon and manganese. These impurities lower its melting-point to about 1200°C; pure iron metals at 1535°0.

Wrought ironi,

This is the purest form of commercial iron. It is 99 per. cent iron and contains less than 0.25 per c

cent of carbon. It is made by removing most of the impurities from pig-iron.

Wrought iron is strong and malleable. It can be shaped by hammering it at about 1000°C.

Steel:

This is an alloy of iron with 015-1.5 per cent. of carbon, mainly as iron carbide and other metals such as nickel, cobalt manganese etc.

Production:

The Bessemer process:

The molten crude iron is in- troduced into the Bessemer convert -er, air or oxygen under pressure is then blown through the grid at the base of the converter. The oxygen then reacts with the impuri -ties and converts them to oxides,

Hydrated Fe20 becomes anhydrous

Fe by the loss of water.

Si

02

Ferrous oxide, if any is present is converted to the ferric state

20

50

(2) Reduction in the Blast Fumace

Iron is then produced in the blast furnace. The furnace is charged through the top with weigh -ed amount of coke, ferric oxide and limestone. The buyeres are fed with a blast of dried air, preheated by waste gases leaving · the furnace. Immediately above the tuyeres, where air is still plentiful, coke burns to carbon dioxide, a strongly exothermic process giving a temperature 1) excess of 1,50000.

+ 02

94,000 cals

liberated.

Higher in the furnace, carpon dioxide is reduced to monoxide by white hot coke.

200

Towards the top of the furnace, at about 600°C., ferric oxide is reduced to iron mainly by carbon monoxide but, to some extent, by coke.

Fe20 + 300

Be20 + 30

→→→¿Fe + 3002

2Fe + 300

Iron is produced as a spongy grey solid which melts as it descend's and finally trickles into the well of the furnace.

The action of limestone is as follows. Most ore contains earthy matter or clays which are essenti- ally silicates. The iron ore if heated alone with these would form ferrous silicate and be lost. But the more active lime, produced by the calcination of the lime- stone in the fumace, effectively removes siliceous matter, forming a fusible! slag of calcium sili- collects at the bottom of the fumace on top of the molten iron, and is periodically tapped off.

cate which

Caco

Cao + 00 1

cao + SiO2 2 Casio,

It must be noted that the whole process is continuous, raw materi als being fed in at top, and iron and slag being removed at the bottom.

Iron ore, cake, I mustone

ware Basse

Jaco

Can 15.02. CoSiDz.

Cost Craco

Thverd

· for the ostane

Forheated air

pig-re

) 520,

502

200

P4010

They are acidic oxides. These oxides can be absorbed by the lining of the converter which is made of a mixture of calcium and magnesium oxides:

Cao + Sio, Mgo + S102

60a0

6Mg0+ P

Cas103 MgSiO3

20a3(PO4)2

2M83(PO4)2

Carbon monoxide bums to give carbon dioxide.

The calculated quantity of carbon and metal (e.g. Nickel, Manganese) is added, so that a steel with the correct carbon content is produced.

Carvester

لعنوان الابه

The composition and uses of the alloys:

Steel: Very hard and tough; its

properties vary with:

the carbon content heat treatment and

other metala present.

a) Hard steel. (0.5

1.5% C),

made hard and tough by quench- ing and tempering, for tools. Stainless steel (18% Cr, 8% Ni), resist corrosion and oxidation better than ordin ary steels, for cutlery and surgical instruments. Manganese steel, very hard and tough, for helmets and machinery for grinding. Tungsten steel, hard even wher hot, for high speed cutting tools.

Brass; (Zn 30% Cu 70%), more

malleable and stronger than copper and superior to steel in workability and resistance to corrosion, for scientific instruments, ornaments etc. Solder; (Pb 60% Sn 40%), it has

low melting point (about 200°C) withstands bending without fracture and solidifies slowly- so that is used for electrical connections and fuse wire.

二期星

Type-metals: (Pb 75% Sb 20% Sn 5%

it melts and flows easily,

日四廿月四年三七九一层公年二十六國民華中

expands on solidification and hard enough to make good caste. It is used for printing.

uralumin: (A1 94% Cu 4.5% Mg

0.95% Mn 0.8%), it is a light alloy, combines high tensile strength with low density, and is valuable in the construct- ion of aircraft,

Exercise Part I:

The extraction of iron in blast furnace is a

A. oxidation

B. reduction Cliquation

D. displacement

E. thermal decomposite

Which of the following state- ments is true concerning the operation of a blast furnace? A. The only function of lime- stone is to help in the production of carbon dioxide. The hot waste gases are usually used for preheating the incoming gases.

C. coke is responsible for the

reduction of the iron oxide. D. Iron pyrites is suitable for

the production of fron.

E. The waste gas is carbon

dioxide only

Pig iron

A. contains many impurities like

carbon, sulphur, silicon,

and phosphorus.

B. has a high hensile strength. C. is very ductile but not

malleable.

D. has a higher melting point

than wrought iron.

E. is produced in an open-

hearth process.

B

lungsten steel is really

a solid solution

. a simple mixture

a chemical compound

D. a stainless steel hard steel

Duralumin. contains.

A. aluminium and magnesium

B. aluminium and tin: 0. aluminium and copper D. aluminium, copper and

magnesium

aluminium, copper, magnesium and manganese.

Steel is superior to pig iro

because

P. it is hard

Q. it can be cast into shape in

moulds.

it can be turned into swords. it is less brittle than pig iron.

it will burn in air.

The molten pig iron is put into a Bessemer converter and air ie blown through the air. P. oxidises all the iron. Q. reduces the iron.

removes a small part of the carbon in the pig iron. removes all of the carbon in the pig iron. hardens the iron.

Stainless steel contains. P. Nickel

Q. Chromium

R. Nickel and chromium S. Tungsten

T. Manganese

Solder

P. has a low melting point Q. has a high melting point R. is a hard alloy

5. is a light alloy

T. contains lead and magnesium

10. In the Bessemer converter, the

basic lining is a mixture of P. calcium oxide and zinc oxide Q. calcium oxide and aluminium

oxide

R. calcium oxide and lead oxide S. calcium oxide and magnesium

oxide

T. calcium oxide, magnesium oxide and lead oxide.

Part II.

1. Distinguish between:

cast iron (b. wrought iron

)` steel

接第五張第二页

(i) The blood conveys oxygen

from the lungs to the

tissues and carbon

dioxide from the tissues to the lungs.

(ii) The blood carries nutri-

ts, after absorption ents, from the small intestine, first to the liver and then to the tissues. (iii) The blood conveys the

excreta (Urea and other nitrogenous wastes) to the kidneys for excretion in the urinë. (2) Chemical co-ordination --

Hormones secreted from the endocrine glands are distributed by the blood to the tissue-cells so as to co-ordinate the work- ing and functioning of the body.

(3) prevention

of infection

The leucocytes possess

phagocytic action. That is the bacteria invading into the body are ingest- ed by the leucocytes.

In addition, the blood can fulfill the function. of the antibody which combats the bacteria and neutralizes their toxins. (4) Regulation of body temperature

The blood absorbs the body heat and carries it to the skin and lungs for dissipation into the air. This is the way to keep the body from being overheated.

(5) Coagulation of blood for

healing process

The blood platelets in the blood form a clot to stop bleeding by the conversion of fibrinogen into fibrin in the pre- sence of calcium ions. and other factors.

(6) Support ---

3. Ans.

The constant pressure in the arteries causes the blood to support the tissues and to maintain the turgidity of the body

(a) When the de-oxygenated bloog passes through the lung; the sodium bicarbonate in the plasma of the blood decomposes releas- ing carbon dioxide which is diffused into the air sace and is expelled. At the same time the haemoglobin in the red blood cells combines with oxygen to form oxy-haemo-globin making the blood oxygenated.

(b) The oxygenated blood con- taining dissolved food reaches the active tissues of the limbs- where the oxygen and dissolved food are given up to the organs* to supply them with energy for activity while carbon dioxide and dissolved wastes are diffus ed into the blood to be carried away.

Ans.

1

A drop of blood from the right ventricle passes through the pulmonary arteries to the lungs and comes out, from the lungs, through the pulmonary veins to the left auricle. In the m auricle the blood passes throug the mitral valve to the left ventricle. Then the blood is pumped out via the systemic arch (aortic arch) and the dorsal aorta to all parts of the body. Finally the blood comes back to the right auricle by the ways of venae cavae. By passing through the tricuspid valve this drop of blood event- ually gets back to the right ventricle.

5. Ans.

Oxygen inhaled passes through the trachea, the bronchus and bronchioles into the lung. Gaseous exchange takes place in the alveoli where oxygen diffuses into the blood of the capillames and combines with the haemoglobin of R.B.C. Blood with oxyhaemoglobin is carried to through the pulmonar vein to the left auricle then to the left ventricle. This blood; is pumped out through the aorta and is distributed by means of arteries to all living tissues of the body for oxidation of food.

Questions for next week

A multiple choice exercise will DE,

given.