1968-02-21 — Page 14

IMMU

三期

日 -廿月二季八六九一零公七十艺4房和

Y

17.768

英文中學會試題預習專欄

化學科

(十七)

三錦剑·

(+)

英文中學會試題預習専欄

物理科

(D)

·陸永熾·

(a) Factors affecting the velocity 21

(1) Wind

a note whose frequency of vibration is twice that of another dote is called an octave above the latter note.

souna in air:

hemistry (17)

Physics (17),

1. (a) Sulphur dioxide may be prepared by the action'

of dilute hydrochloric acid on, sodium sulphite.

Some sodium sulphita crystals are placed in

a flat-bottomed flask fitted with a rubber bung through which pass the stem of a dropping funnel and a delivery tube, A fairly strong solution of hydrochloric acid is put into the furmel and is dropped on to the sodium sulphite. Sulphur dioxide is evolvad,

NaO

2301 ❤ NaCl •

So2 H2O

The gas is passed through a drechsel? bottle containing water to remove the tydrochloric acid vapour. Then it is passed through a drechsel bottle containing concentrated sulphuric acid in order to dry th gas. The dry gas is then collected in gas jars by downward delivery.

(b) Add dilute sulphuric acid slowly to some

cupric oxide contained in a beaker and stir the mixture. Repeat the process until the black oxide has completely dissolved and the beaker contains a blue solution of cupric sulphate.

Cuo *

H2SO4

·

CuSO4

+

H2O

Evaporate some water from the solution until one or two small crystals of hydrated, copper sulphate appear at the bottom of the beaker. The solution is then saturated. Allos, the saturated solution to cool. A crop of blue crystals, will crystallise out of the solution.

CuSOL

5H2O CuSO, *Hạ©

The crystals may be separated from the solution by filtration, and dried between two sheets of filter paper,

(e) Titrate the given sulphuric acid solution

against tho. given caustic soda to find out the volume of açád required to neutralise eatly 25 ml. of caustic soda solution.

230 N GÍACH...

•

Na230 21.0

Suppose v al. of the acid solution are frequired to pèutralise, 25 ml. of the given 'naustic soda solution, Take a large beaker and

sixture the two solutions in the ratio, 2 v parte by volum of acid to 25 parts by volumDB of alkali. The resulting mixture will be a solution of sodium hydrogen sulphite.

2NaCh

Na 30 240

31. Solution

(4) 4 transverse wave is one that causes the

particles of a medium to vibrate at right angles to the direction in which the wave ta moving.

A longitudinal wave is one that causes the particles of the medium to vibrate parallel to the direction in which the wave is moving.

(b) When sound wave falls onto a hard surface it

is reflected. Echoes are the results of reflection of these sound waves, Due to the persistence of sound in our ears, a diatirici scho cannot be heard unless the reflecting murface is more than 55 feet from the source of sound.

When the reflecting surface is less than this distance the echo follows so closely with the direct sound wave that they cannot be distinguished as separate sounds. It merely Impresses as a prolonged sound. This effect is known as reverberation.

(e) The ship is approaching the cliffs,

Assuming that the cliffs are a ft. ahmad' and ' the velocity of the ship is v ft./seo The speeds of wind and water current are negligible also,

(32. (a)

Since the echo took 3 sec. to return for the first time, the ship had already sailed 3v ft. towards the cliffs

1.29 3v) - 1100 x 3

(1)

1 min. later the ship was ́then tv. 3v - 60v) from the cliffs, and 2 sec, inter it was (65v) ft, from the cliffs,

63v) - (dam66v) •

126v $125

• 6 m. pah.

Subs, into (1) 2

• 3300

1636.8 ft.

(2)

Wind may alter the velocity of sqund in air. Sound is in direction of the wind, its welocity is greatly increased. If the direction of sound is into the wind, it will be alowed dowEL»

(11) Temperature

If the air temperature increases et constant pressure the air will expand- according to Charle's Law, and therefore becomes less dense,

Since the velocity of sound is proportional to the square root of the ratio of pressure to density an increas in this ratio, therefore, increases the velocity of sound in air.

(111) Pressure

In accordance with Boyla's Law, the pressure of a fixed mes is inversely proportional to its voluma. Thus, at constant temperature the ratio of pressure to density will always remain constant, however mish the pressure is decreased.

(d) Velocity of sound in air 330 m/sec.'

Velocity of sound in water - 1650 m/sec. Velocity of sound in iron 5000 m/sec, Frequency of tuning fork - 512 c.p.5.

Velocity of sound » frequency x wava-length

330

wave-length of sound in air

512

·

velength of sound in water -

wavelength of sound in iron -

64.4 cm

1650 512

5000 512

- 3.22 .

- 9.77 #

ar

H230

J. Mach!

NaHSO

Evaporate the solution until it becomes saturated. On cooling the solution, crystale

note

HUN ON

of sodium hydrogen sulphate will settle to the bottom of the beaker. The crystals are separated from the solution by filtration and are dried between two sheets of filter paper. 2. (8) When heated to a temperature of 300°C, farrous sulphate crystals will lose their green colour as they lose all their water of örystallisationer In the absence of eir, the anhydrous salt is. white.

F#347H20 - Peso green crystals

77

white solid

On further beating, anhydrous ferrous sulphate decomposes to yield sulphur dioxide, sulphur trioxide and a reddish brown solid residus, ferric oxide.

27.50% - F•2032 • 502 ~ • S03

Ferrous sulphate has been used tw centuries in the making of ink. Permanent, la! contains farrous sulphate and gallic acid 10 water. Ferrous sulphate le a constitusot of “law sand in which the sulphate acts as a wand-killər.

(b) two processes of manufacturing sulphuric acid

(1) The Lead Chamber process;

(11) The Contact procesa,

For bötn processes;-sulphur dioxide 18 needed as the raw material. Sulphur dioxide may be obtained in a number of ways, (1) Burning sulphur - Bulphur dioxide is

obtained in large quantities by burzing] sulphur in air.

02 9021)

2) Roasting 'spent oride" or ores containing

sulphur - The gas obtained by roasting ores is immediately converted to sulphuric seid,

4FeS2 • 110. 2020.

1ron

pyrite

8502 ↑

3) Anhydrite process - Calcium sulphate is

rosated with carbon in a rotary kiln,

Sulphur dioxide is obtained by the following! resations),

another by (3) quality.

the cliff

#p.a.

depends on las vibrating Iving a-

#☎ musical

of such sound. tion of them of Kirregular

lity of a musical

istinguish from one Feb (2) intensity and

Questions for next week;

33. (a) How does the frequency of vibration of =

stretched string depends on (1) its length (11) the tension?

(b) A wire of fixed length is correctly tuned to various forks by altering · its tension, with these results:

Iraq, of fork c.p.s. (m) 256 320 362 512

Tension of wire gn.wt.(T)] 1600 2500 3600 | 6400

Using graph paper, plot n against square roat of T, and from the grach find the tension when tha frequency is 480 c.p.8.

(c) A sonometer 1 metre long omits a note or

Frequency 300 per sec. when under a tension of 2 kg.wt. Calculate (1) tha length at whion it will have a fréquency of 600 per sec., the tension being unaltered, (ii) the frequency when the tension is increased to 8 kg. wt., the length remaining 1 qėtra,

LIBRARIES:

Pitch means the lownese and highness of a musical note. Pitch depends on the frequency of vibration of the source; the greater the frequency, the higher will be the pitch of the sound produced.

intensity of a sound or a musical note defined as the rate of flow of energy pr mit area perpendicular to the direction of the wave: It S direcüly préportional to the square of the amplitude of the wave of the sound. Quality

MUDICES Ruta cons2818 of several different frequencies blended together. The strongest audible frequency present is calle the fundamental and gives the note ita characteristiɑ pitch. The others are over tones,

-

and these determine the quality of a sound.

C$90,

糖 Cas

4CO - Cas • 20a9 - 8Ca0 •

(1) The Lead-Chashar Process

4.00 T LCO2 f 85021

P

6 mixture of air, sulphur dioxide and oxidee of nitrogen is passed “into lead chembers, into the top of which watar im sprayed, tea

NOZ

H2Q

·

• NO 902

Haso

The nitric oxide, which serves as a catalyst, is immediately, oxidised to nitrogen peroxide by the air present, ang the cycle is again repeated»,

2N0

nitric oxide

On

2002 nitrogen peroxide

(11) The Contact Process

A mixture of sulphur dioxide and pxygen are made to combine at temperature. between 400°C and 500°C using a catalyst such as platinum or vanadium pentoxida.

2902

G

2903

The sulphur trioxide is passed inte

J

34. (a) What is meant by resonance?

(b) What is the distance between the first eco

second position of resonance of (1) an open tube (11) a tube closed at one end? (c) Describe an experiment to determine the

velocity of sound in air using a resonance tune and a tuning fork of known frequency. (d) A vertical glass tube is filled with water which is allowed to run away slowly at the lower end. At the same time a tuning fork 1. maintained in vibration above the upper end which is open. As the tube is emptied, two positions of resonance of the air colum are observed, the distances between the correspond- ing water surfaces being 27.5 cm. Find the frequency of the fork if, during the experiment, the velocity of sound in air in the tube above is 330, metres per sec. State, with an explanation, how the above distance will alter if the temperature of the zir rises.

98.5% sulphuric acid in cast-iron containers. hater or dilute sulphuric acid is passed into the tanks at the same time, so as to maintain the concentration of the acid at 98.5%/

Questions for next week (18) |

2. Describe the properation of crystals or two

different salts from sulphuric acid and sodium hydroxide.

4.88 gm. of barium chloride crystals (BaCl2*2820) were dissolved in water. To the solution waa added 100 c.c. of a normal solution of sodium sarbonate and the precipitate formed filtered, carefully washed and dried. Calculate (a) the weight of solid obtained, and (b) the volume of 8/5 hydrochloric acid which would be enquired to react with the excess of sodium carbonate in the filtrate.

2. (1) By referring to ita action on the following,

describe the properties of concentrated sulphurde acid:

&

(a) modium chloride, (b) carbon. (a) papar, (d) aopper. oxide.

́(11) Give a list of the important usee of

sulphuric acid,