1973-04-23 — Page 21

T-BAR D-TA=FIABI WAH KIU YAT PO

報日僑華

育教信

大橋

30

1973英文中學會考試題預習專欄 |

化學科

(廿六)

Chemistry (26)

Solution for

H2SO

98.

week

SO

Part II

1. (a) Each ml. of acid solution weighs 1.198 gm. and contains

0.27 x 1,198 em H2SO4

The weight of H250 in 1 âm is

100 x 0.27 x 1.198 - 324 gm.

molecular weight of H

In 1 dm of solution

MH

One dm

324 gm.

98.1 gm/mole

3.30 moles HSO

of solution contains.

3.30 moles HSO

is 3.30M

(b) The weight of water in 1am

of solution (1198 324)

874 gm.

moles of solute

Kg of solvent 3.3 moles HSO

Molarity

hence the.

0.874 Kg H20

378 M

From the equation for th reaction.

2HC1

2003

2NaCl + H20

CO

We can see that 2 moles of acid

react with 1 mole of the base.

20.om of 0.1 M HCl contains.

20

0.002 mole of HC1

x 0.1

15 cm

on of aqueous Na,00 must

contain half this number of moles,

.e. 0.001 mole Na,CO2•

dm must contain

of

Na2CO

solution

1000

x 0.001 0.066 mole

The sodium carbonate solution

is 0.066 molar.

15. Metals (1)

The general properties on metals and their differences from non- metals:

The following table shows the essential physical and chemical differences between metals and

non-metals.

non-malleable

how density

Bad conductors of heat and electricity.

Are not

IodineTM has a density of 49. sodium and potassium: are lighter than water.

graphite) and iodine Carbon (in form of

plastic sulphur is malleable

are lustrous.

of electricity. Graphite is a good conductor

Lead, sodium and potassium

non-metals

Important Exception

Do not possess this lustre

srooμos 400 BIB

snoIoUos

Low melting and

boiling points

Metals

characteristic

possess a

Are malleable

High density

Good conductors of heat and

electricity

Are sonorous.

High melting

and boiling

points

1481T

set1cedoxa Tebisiya

by water

They frequently dis-'

is exceptional). Their normal oxides are solve in dilute acids with displacement of hydrogen (nitric acid

They are electro- Metals

positive

true salts, and are not Their chlorides are decomposed by water. basic

They seldom form hydride when they do so, these decomposed by water e.gu compounds are readily

Call + 2H 0

Ca (OF) + 2H

Non-metals

They are electronegative Are not acted upon by dilute acids

form hydrides (e.g. SH2, OH2, NH2, CH), which Their chlorides are not decomposed by water true salts and are

They

Their normal oxides are acidic N

are not

decomposed

insoluble in dilute sulphuric Copper and lead practically. and hydrochloric acid

Important Exceptiona

carbon is scarcely either one or the other

Carbon tetrachloride CC1 is only slowly decomposed by water..

The reactions of the metals toward air, water and dilute acids:

This work will be based firmly on the metal activity series.

The activity series is a series of metals arranged in decreasing order of reactivity, which is:

1. potassium

7. Tron 8. Till

Sodium Calcium

4. Magnesium

Aluminium

Zinc

Potassium (K)

Magnessium (Mg) burn readily Aluminium (A1) to form oxide

Water on metal

react vigorously in the cold to give hydrogen react to give hydrogen when heated with

reversible: steam:

reaction

Dilute acids

vigorously to.. given hydrogen react very on metal

react to give

hydrogen

Air or oxygen

on metal

Metallic

element

Sodium

Calcium

Zinc

(Fe)

ΠΟΣΤ

9. Lead

10. Hydrogen 11. Copper

12. Silver

no action.

no action

Tin

Lead

(Pb)

form oxides

when heated

Copper

(Cu)]

(us)

Reduction of the oxides of the

metals:

1. Hydrogen or carbon monoxide on i) oxides of potassium, sodium,

calcium, magnesium, Aluminium and zinc are not reduced.. ii) oxides of iron is reversible,

-期星

Fe203

300

2Fe

3002

Fe2O3 + 6H2

2Fe + 3H20

oxides of lead and copper

Pbo + Co

CuO+00

are reduced, e.g.

Pb 400

Cu

Pbo

H2

Pb+ H2O

CuO + H2

2. Carbon on 1) oxideg

calcium, sodium,

and alum-

inium are not reduced. ii) oxides of zinc, iron, lead

and copper are reduced..e.g.

Zno

PbO +

Zn + .00 2Fe + 300

+30

Pb + Co Cu +00

Cuo + 0

The liberation and purification of metals by electrolysis.

1. Liberation of metals..

The reactive metals could be prepared by the electrolysis of fused compounds (usually the chloride).

Electrolysis of molten sodium chloride.

The electrolysis of fused. sodium chloride to give its component elements is not practicable owing to the ease with which molten sodium dis- solves in the molten electro- lysis to give a "metallic fog Electrolysis of this electro- lyte does not give rise to

serious loases of sodium by the formation of metallic fog.

Anode carbon Cathode: steel

Ionisation reaction:

NaCl

Na + CL

At cathode. Na ions are attracted and, since they are the only ones present, they are neutralised. Sodium metal is formed and rises to the surface.

2N+

anode

Na

C1 ions are attracted and chlorine is liberat -ed!

201

201

201 2e

This reaction is used to prepare sodium metal commercially.

2. purification of metals:

In the electrolysis of copper sulphate sodium with an impure copper anode and a pure copper cathode leads to the refining of the anode material. Impure coppei leaves the anode, and pure copper is deposited on the cathode. Similar methods can be used to refine nickel and lead.

The chief uses of metals. Magnesium: light alloys (e.g.

magnalium, electron) in engine -s and aircraft; flares and fireworks (with an oxidising agent)

Aluminium: as domestic cooking utensils; electric cables; light alloys; pint, and thermit process for welding iron:

2AI + Fe203

Al2O3 + 2Fe

Zinc: in galvanising iron or wild steel; alloys (e.g. Brass, German silver, and die-casting alloys); as the cathode of dry batteries, and in the extract- ion of silver and gold. Iron and steel: railings, pipes,

girders, bridges, cars and engines.

Lead: in the building industry (ee as sheet lead for roofing); in chemical industry (e.g. lead chamber process to manufacture of sulphuric acid); alloys (solder, pewter and type,

metal etc.).

Copper: alloys (e.g. brass, bronze

gun-metal, bell-metal and coinage alloys), water pipes, heat and electrical conductors

(e.g. boilers, cable).

Exercise

Part I

1. Alkali metals are usually

extracted by

A. reduction of oxide using

carbon: inonoxide

B. the thermite process C. roasting the sulphide

D. electrolysis of the chloride

solution

日三廿月四年三七九一滕公年二十六國民華中

E. electrolysis of the molten

chloride

Calcium differs from magnesium

in that calcium

A. combines directly with nitrogen on heating

B. has a soluble bicarbonate

has a hydroxide which is only slightly soluble in water D. forms a sparingly soluble

sulphate

A

forms a chloride which under goes partical hydrolysis when its aqueous solutions are heated.

The dustile nature of metals means that

A. they are strong

B. they are hard.

C. they are soft.

D. they can be rolled into thin

sheets

E. they can be drawn into wires

4. The malleable property of metals

means that

A. they can be drawn into wires B. they can be rolled into thin

sheets

C. they are cooled in moulds D. they are hard

E they are strong

5. Chemical activity of the metals

A increases with decreasing electropositive character

B. increases with decreasing electronegative character

C. increases with increasing at

atomic weight.

D. increases with increasing

atomic number

E. decreases as we pass through

the electrochemical series form potassium to gold

Magnesium reacts with dilute acids displacing hydrogen, but lead does not. This indicates that

P. magnesium is less reactive

than copper.

Q. lead is found above magnesium in the electrochemical series

R. Magnesium is more electro-

positive than hydrogen

5. Magnesium is more electro-

positive and lead less electropositive than hydrogen T. Lead is inert.

Common solder contains

P lead and aluminium

Q. Lead and tin

R. lead and antimony S. lead and zinc

T. lead and magnesium

8. Duralumin contains:

P. aluminium and copper Qaluminium and magnesium R. aluminium, copper and

magnesium.

S. aluminium and tin

T. aluminium and antimony

9. If aluminium is burned in air,

P

and excess water is then added:

the products will be

aluminium hydroxide

Q. aluminium oxide solution

R. aluminium hydroxide and

ammonia

S. aluminium nitrate.

To basic aluminium nitrate

10. If potassium burns in ai

produces

12.

P. potassium peroxide and

potassium oxide

Q. potassium peroxide and

potassium nitride

R. potassium oxide and potassium

nitride

S. potassium oxide only

T. potassium hydroxide and

hydrogen

1.32 gm of 'n alloy of alumi nium and zinc when dissolved in excess dilute hydrochloric acid liberated 870 ml. of hydrogen (collected dry at s.t.p.). What was the percent

weight of aluminium

thete?·

A. 15 per cent.

B. 26 per cent. C. 35 per cent. D. 48 per cent E. 60 per cent,

1.00%

gn. of a metal oxide when completely converted gave 2.33 gm. of the corresponding sulphate.. The mass number of the metal was 91. A formula which corresponds to these results is:

A. MO

B. MO

C. MO2

D. M203

E. MO