1974-02-04 — Page 15

REFERENCE LIBRARY

4E01974

WAH KIU YAT PO

would fill the tube and 'suck' back

有教儒華真三第張四第1日三十月正年寅甲歷表

into the flask. An inverted funnel Uses:

橋

is attached to the tube and afrakge

ad so thab ih-fia is just below the surface of water in a beaker.

Ammonium -

:1874中學會考試題預習專欄

化學科(甲) (十三)林景源

CHEMISTRY (13).

Suggested answer for last week:

1. (1) Chlorine combines directly.

with tin to form stannic chloride, however the reaction is catalysed. by a

Morrace of water.

2012

SnCl

(11) Chlorine reacts with ammonia by replacement of the hydrogen.. Thus in presence of excess chlorine hydrogen chloride and nitrogen tri- chloride are formed.

OH + 3012 NHL

3HC1 NC1+0 However, in the presence of excess ammonia, the nitrogen tri- chloride is decomposed:

NH, OH NC

3HC1 + H20 So that the over all reactio 301+8NH, OH ——— 6NH C1+8H2O + N ̧

fa:

(iii) Aluminium is a strongly reducing metal, it combines very. igorously with chlorine yielding the chloride,

2A1 +

(iv) If chlorine is passed into a aqueous solution of sulphur dioxide (sulphrous acid) sulphuric acid and hydrochloric acid are formed.

SO

- C12+ 2,0 → R2SO + 2HC1

(v) Carbon monoxide will unite with chlorine, in sunlight or in presence of heat animal charcoal to form carbonyl chloride COC1. Also known as phosgene...

CO + Cl2

COC1

The simplest laboratory preparatiş of chlorine without heat is by the action of potassium permanganata with concentrated hydrochloric acid

+5012

2KMnO +16HC1 ✈2KC1+2MnCl2+820

As 100 g of the conc. acid ootad 6.5 g HC1, 200 g will contain 73 8

e. 2 moles. According to the quation given above for the prepar- tion of chlorine 4 moles hydrogen hloride will produce one mole of hlorine 1.0. 22.4 litres at N.T.P., 2 moles will therefore produce 11.2 Litres. At the temperature and pressure of the experiment these 11.2 littes will represent

760 290 750

11.2 x

273 12.1 litres, The maximum yield is 12.1 litres.

(1) If a filter-paper soaked with warm turpentine is dropped into a Jar of chlorine, there is a vigorou reaction and clouds of soot are formed. The chlorine has extracted. the hydrogen from the turpertine, leaving the carbon.

8C110C + 16RC1

(11) When chlorine is passed throu a sölution of ferrous chloride, the colour of the solution changes from pale green to yellow, showing that the ferrous chloride has been oxid- 1sed to ferric chloride.

2FeC12

+ C12

→ 2FeC13

Chloride.

Properties:

It is a colourless gas, when breath Sodium

ed, the hydrochloric acid formed

gives it a choking, irritating anell.

It is very soluble in water, however than air.

Chemical:

1. Dry hydrogen chloride is not

acidic and will not affect dry litmus paper.

2. It neither burns nor supports

combustion..

With ammonia, white clouds of ammonium chloride smoke are immediately formed.

NH3 + HCL

With reactive metals on heating to give the anhydrous chloride.

Zn + 2HC1

Fe+ 2HC1

FeCl2

Hydrochloric acid and hydrogen chloride in toluene:

We know that hydrogen chloride is ä covalent compound, but that when it

Potassium

Calcium

Zinc

Silver.

報日僑華

Uses

In dry batteries,

Leclanche cells.

In the manufacture of Caustic soda, chlorine and sodium by electroly

sie.

In the manufacture of

washing soda by the Salm process:

To the manufacture of bleaching powder, and other sodium compounds

As a fertiliser.

As a source of caustic potash and potassium nitrate.

As a drying agent.

As a source of calcium metal.

As a dehydrating agent. Its solution in conc, hy drochloric acid is uses' as a flux in soldering. In making printing-out papers in photography.

dissolves in water it losises, giv- Tests for chlorides, Bromides and ing hydroxonium ions and chloride ions.

HG1 + H2O

solutions of acids. Hydroxonium ions are present in all

Hydrogen chloride does not donize. in dry toluene, and is present as covalent compound. The toluene sol- ution differs from the aqueous aol- ution as follows:

HCI in water

Elect It conducte rical electricity conduct ivity:

[HC1 in dry

toluene.

It does not. conduct electricity

ActionHydrogen liber It does not on Mg,ated

form hydrogen Zn, few

ActionIt turns the on in-colour of dicator indicator

Action Carbon dioxide on car produced. bonate

Action Ammonia

on KH, dissolves

No effact

It does not. react with carbonates

A white Ppt

ferned.

Tast for hydrochloric acid Added a solution of silver nitrate into the hydrochloric acid (or any of its salts). A white ppt. of in- soluble silver chloride is at once. obtained. The ppt dissolves again very easily in a dilute solution of ammonia.

AgCl + HNO3

HC1 + AgNO3

Chloridee: Hydrochloric acid forms only one se ies of salts known as the chlorideï All of these are freely soluble wi the exceptions of lead, silver and mercury(1) chlorides.

Preparation

By neutralisation of an acid with an alkali, e.8. potassium, sodium and ammonium chlorides

' Kaol + HC

2H Ở + Ngà

By the action of the acid on a metal, e.g. zinc and ferrous. chlorides.

Zn + 2HC1

Hol

ZnCl

By the action of the acid on a metallic oxide or carbonate, calcium chloride.

CaCO3 + 2HC1

CaCl

By double decomposition, e.g. lead (111) When chlorine is passed into and silver chlorides.

a solution of potassium bromide',: th

solution turns red as free bromine

is liberated.

2KBr + C1— 2KC1 + Br

Hydrogen chloride

Preparation:

Hydrogen chloride is usually made by the action of conc. sulphuric acid on common salt.

NaCl + H2SO4

or 2Naci +

NaHSOHC1

Na

la 2501

+ 2НС1

It is heavier than air, and so can be collected by downward delivery.

The large quantity is now made. direct synthesis from hydrogen and chlorine. These are both obtained by the electrolysis of bring solution in the manufacture of caustic soda. The hydrogen is then burnt in an atmosphere of chlorine in silica vessels.

2XC1

H

Bolution of hydrogen chloride in Water is called hydrochloric acid, This cannot be made by leading hydrogen chloride directly into water by an ordinary delivery tube. The gas is so sbbuble that water

Iodide:

With silver nitrat solution,

chlorides gives a white ppt.

insoluble in nitric acid but soluble in ammonia.

KC1 → AgNo2-

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S. AB! AB = SB: SB (TANYO ;) L=10h

B'C" : BC = SB' GB $ps 成比例)

KNO2 + ABC) 6 A'B' ? AD = 'B'EM? BC (T

Chlorides give chlorine when

heated with sulphuric acid, and manganese dioxide.

4NaCl+MnO2+ 4H2SOL

4NaHSO+MnCl2+20+ Cl2

7. ABCO'EU AB (DE(R)

8. A'B' TAB = B'C' BL (A))

邊對應邊成比例)

When a miture of a chloride, con sulphuric acid, and potassium: dichromate are warmed, red vapor of chromyl chloride, Cro C1, are formed. This give yellow ppt, or lead chromate when passed into lead acetate solution."

9

2HC1

H.Cro

(CH_COO)¿Pb.

РОСГОН + 2СН-СООН Chronyl chloride also dissolves in caustic soda solution to form yellow sodium chromate...

Bromide with silver nitrate sol ution to form a pale yellow

silver bromide, slightly soluble in ammonium hydroxide.

AgBr

KBr+ AgNO3 KNO

Iodide with silver nitrate solut ion to form a yellow silver lod ide, insoluble in ammonium hydr oxide.

KNO

KI+ ARNO,

Question for this week:

Using ammonium chloride as the material, outline one method for the preparation of a reasonably conc. solution of hydrogen chlor- ide.

Describe what you would observe

and explains what happen when

1) dilute hydrochloric acid 18. added to a solution of lead nitrate and the resultant mixture heated.

11) A jar of hydrogen chloride

placed mouth to mouth with a Jar of annonia.

三項各等分别一比例之 相等三項,則其餘一項

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(12)

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堅道書院主

H2SO

By direct combination of the metal with chlorine 1 ¡e.g. copper and ferri chlorides.

化二科(乙) (十二)主兆交

第十三講

Pbs+ 2HC1 > Pac12

Cu + Cl2

Properties

Most metallic chlorides yield hydrogen chloride with conc. sulj uric acid. Chlorine is evolved or heating a mixture of chloride,

manganese dioxide and sulphuric acid.

2. Some chlorides decompose on heat

ing to give either the elements a lower chloride, e.g.

CuCl

2

Cu C12

Other chlorides form the corres- ponding oxides and chloride when heated in air.

4FeCl2 + 302

F203.

+401

4. When it is heated ammonium chlor dissociates into two simpler gas eous compounds, ammonia and hydr gen chloride, when cooled, these gases recombine to form solid ammonium chloride. This sort of decomposition is called thermal dissociation.

NKCI

NH, + HCl

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