form 4 chem chapter 4

8/13/2019 Form 4 Chem Chapter 4

http://slidepdf.com/reader/full/form-4-chem-chapter-4 1/21

Chemistry – Form 4 Page 56

10 The Chemistry of Characteristic non-metals and theircompounds.

10.1 NITROGEN 10.1 NITROGEN 10.1 NITROGEN 10.1 NITROGEN

See Chemistry for You - Haber process - pg. 240-1, 243- Uses of Nitrogen – pg. 315

See written notes on Nitrogen properties and uses.

o Nitrogen is a Group 5 element.

o Nitrogen makes up about 78% of the atmosphere by volume but

the atmosphere of Mars contains less than 3% nitrogen.

o The element seemed so inert that Lavoisier named it azote,

meaning "without life".o However, its compounds are vital components of foods, fertilizers, and explosives.

o Nitrogen gas is colourless, odourless, and generally inert.

o As a liquid it is also colourless and odourless.

o When nitrogen is heated, it combines directly with magnesium, lithium, or calcium.

o When mixed with oxygen and subjected to electric sparks, it forms nitric oxide (NO) and

then the dioxide (NO2).

o When heated under pressure with hydrogen in the presence of a suitable catalyst ,

ammonia forms (Haber process).

o Nitrogen is "fixed" from the atmosphere by bacteria in the roots of certain plants such as

clover. Hence the usefulness of clover in crop rotation.

Isolation of Nitrogen from Air:

In the lab: There is never any need to make nitrogen in the laboratory, as it is readily availablecommercially or through in-house air liquefaction plants. However the decomposition of sodium

azide is one route to N2 and decomposition is ammonium dichromate is another. Both reactions

must only be carried out under controlled conditions by a professional.

NaN3 (300°C) 2Na + 3N2

(NH4)2Cr2O7 N2 + Cr2O3 + 4H2O

Industrially: Nitrogen is made on massive scale by liquefaction of air and fractional distillation

of the resulting liquid air to separate out oxygen and other gases. Very high purity nitrogen is

available by this route.




Test for Nitrogen

1) Has no colour or smell.

2) Has no effect on moist litmus paper or moist universal indicator paper, it is neutral.

3) Will put out a lit splint.

There is no specific test for nitrogen. It is notable for its inertness (it doesn't do much!).

a. Complete the following:

________ by volume of air is nitrogen. The formula of the nitrogen molecule is ________.

Compared to oxygen, nitrogen is fairly __________________ (reactive, unreactive). But when

there is a spark, nitrogen reacts with ________________ from the air.

b. Nitrogen is obtained from air by ____________________________________________.

c. Give one use of nitrogen _______________________________________________________

d. In the Haber Process, nitrogen is reacted with hydrogen to form __________________ which

has the formula __________.

e. The equation for the Haber process is _____________________________________________

f. Ammonia is used to make ________________________ and _________________________

Ammonia – NH3

Ammonia is prepared in the laboratory by heating a mixture of ammonium chloride (NH4Cl) and

calcium hydroxide (Ca(OH)2). The apparatus for the preparation is shown below.




Uses of ammonia

o Manufacture of nitric acid

o As a refrigerant

o As a source of nitrogen

o Manufacture of nylon, plastic, rayon, dyes

The Haber Process

We have already seen that the reaction in which nitrogen and hydrogen combine to form

ammonia has much industrial importance. This process of preparing ammonia for the

manufacture of chemical manures is known as Haber process. See the following equation.

N2 + 3H2 2NH3 + heat

One mole of nitrogen and 3 moles of hydrogen combine to form 2 moles of ammonia.

The state when the rate of both the forward and backward reaction becomes equal

is called equilibrium. At equilibrium, the rate of forward reaction will be the same

as that of the backward reaction.

The German scientist Fritz Haber developed the method of industrial production of

ammonia. Haber was searching for an abundantly available nitrogen compound that can

be used in the manufacture of explosives and fertilizers. This led him to the invention of

Haber process.

Haber was trying to make ammonia by combining nitrogen and hydrogen. He discoveredthat if pressure, temperature and catalysts are properly regulated, the inactive nitrogenwill react with hydrogen to form ammonia.

NH3 - Ammonia Molecule NH4 -

Ammonium Ion




Le Chatelier principle

In the production of ammonia, both the reactants and the products are gases. So,

pressure has its effect in this reaction. As in the case of concentration, temperature

and pressure can affect the equilibrium.

Henry Le Chatelier put forward a principle regarding the effect of concentration,

temperature and pressure on equilibrium. If a system in equilibrium is subjected to

a change of pressure, temperature or concentration, the equilibrium is shifted in

such a way as to cancel the effect of that change. This is known as Le Chatelier

principle.

The fountain Experiment (See GCSE Chemistry pg. _______)

Add two drops of phenolphthalein into the

water taken in the vessel. When water is

dropped into the flask using a filler, a fountain is seen.

The fountain experimentdemonstrates the violence with

which ammonia is absorbed by water.

The ammonia absorption by water

reduces the pressure in the flask, sothat water escapes from the upper,narrow opening of the tube. Thus,the increased surface of the waterleads to an increase in the speed of

absorption till the water shoots intothe glass flask like a fountain. Duringthe process the colour of theindicator changes due to the alkaline

effect of ammonia




- Chemical properties of NH3:

combustion in oxygen

Ammonia burns in air slightly enriched with oxygen to produce nitrogen and water.

4 NH3 (g) + 3 O2 (g) 2 N2 (g) + 6 H2O (l)

catalytic oxidation (to give NO and H 2O);

In the presence of a catalyst, ammonia reacts with oxygen to form nitrogen monoxide and water.

(Platinum/Rhodium catalyst) 4 NH3 (g) + 5 O2 (g) 4 NO (g) + 6 H2O (l)

reaction with hydrogen chloride

Ammonia reacts with hydrogen chloride to form ammonium chloride (dense white smoke)

______________________________________________________________________________

reducing action on copper (ll) oxide.

Ammonia reduces copper (II) oxide to copper

3 CuO (s) + 2 NH3 (g) 3 Cu (s) + N2 (g) + 3H2O (l)

alkalinity Is alkaline in water: NH3 (g) + H2O (l) NH4OH (aq)

neutralisation of acids - reacts with acids to form ammonium salts.

NH3 (g) + HNO3 (aq) NH4NO3 (aq) (Ammonium nitrate is an important fertilizer)

FERTILIZERS e.g. NH4NO3, (NH4)2SO4

There are 2 kinds of fertilizers:1. Straight N fertilizers contain only nitrogen e.g. ammonium nitrate

2. NPK fertilizers contain nitrogen (N), phosphorus (P) and potassium (K). Usually a

mixture of ammonium nitrate, ammonium phosphate and potassium chloride.

Plants need nitrogen (essential for proteins), potassium (to resist frost and disease) and

phosphorus (root growth and seed formation). Disadvantages of fertilizers:

a) may change soil pHb) may harm plants and animals in the soil

c) get washed out of soil and cause water pollution

d) allow elements not required by plants to accumulate in the soil.

Ammonium salts decompose on heating: NH4Cl (s) NH3 (g) + HCl (g)

(NH4)2CO3 (s) 2 NH3 (g) + CO2 (g) + H2O (l)



Chemistry – Form 4 1

Oxides of nitrogen, NO and NO2

NO

It is a colorless gas. When it meets oxygen, it reacts to form brown nitrogen oxide. Nitrogen monoxide is produced by reacting moderately concentrated nitric acid on

metals.

The manufacture of nitrogen monoxide as the first stage of the Ostwald process.

THE OSTWALD PROCESS

a) Ammonia is oxidized to nitrogen monoxide (NO); Platinum/Rhodium catalyst at 900oC

4 NH3 (g) + 5 O2 (g) 4 NO (g) + 6 H2O (l)

b) Nitrogen monoxide is cooled then oxidized to nitrogen dioxide by mixing with air.

4 NO (g) + 2 O2 (g) 4 NO2 (g)

c) Nitrogen dioxide is reacted with water and oxygen to produce nitric acid.

4 NO2 (g) + O2 (g) + 2 H2O (l) 4 HNO3 (aq)

Revision of the formation of oxides of nitrogen in the internal combustion engine and theirremoval by a catalytic converter. (see Chemistry for You pg. ______)

NO2

Physical properties & test for the gas

o Nitrogen dioxide is a brown poisonous gas.

o Has a pungent irritant smell.

Laboratory preparation of nitrogen dioxide by the thermal decomposition of lead nitrate

It is produced in the laboratory by heating

lead (II) nitrate.

When heated lead (II) nitrate decomposesto lead (II) oxide, nitrogen dioxide andoxygen.

2 Pb(NO3)2 (s) 2 PbO (s) + 4 NO2 (g) + O2 (g)




Chemical properties of nitrogen dioxide:

Action with water (linked to acid rain)

When it dissolves in water, it forms a pale blue solution. This solution is acidic.

2 NO2 (g) + 4 H2O (l)

HNO3 (aq) + HNO2 (aq)Nitrogen dioxide + Water nitric acid + nitrous acid

That’s why nitrogen dioxide when present in the atmosphere, contributes to ACID RAIN .

Action with burning magnesium,

o If magnesium is burnt in it, magnesium oxide and nitrogen are formed.

o The hot flame decomposes the nitrogen dioxide into nitrogen and oxygen.

o The magnesium then reacts with oxygen.

4 Mg (s) + 2 NO2 (g) 4 MgO (s) + N2 (g)

Thermal dissociation of N2O4: When dinitrogen tetroxide is heated, it decomposes into

nitrogen dioxide.

Dinitrogen tetroxide Nitrogen dioxide

Light yellow Dark brown

Decrease pressure

N2O4 (g) 2 NO2 (g) Increase pressure

Pressure affects the rate of the equilibrium. If you increase pressure, more dinitrogen tetroxide is

made. If you decrease pressure, more nitrogen dioxide is made.

• Nitric Acid Manufacture of nitric acid by the Ostwald process (see previous page)

Uses

The majority produced is used in the

manufacture of ammonium nitrate a

nitrogenous fertilizer.

Several explosives are made using nitric

acid, including TNT (trinitrotoluene),

nitroglycerine.

The manufacture of nylon requires hexanedioic (adipic) acid, produced using nitric acid.

It is also used in the manufacture of chemicals, e.g., in making dyes, and in metallurgy, ore

flotation, etching steel, photoengraving, and reprocessing of spent nuclear fuel.




Metallic Nitrates

o General methods of preparation

HNO3 (aq) nitric acid reacts with metals to form the metallic nitrates e.g. Cu(NO3)2 see pg. 63

o solubility – all nitrates are soluble

o action of heat on nitrates see notes pg. 48o test for NO3 see notes pg. 45

10.2 Sulphur and its Compounds

Allotropy of sulphur. – Allotropes are different forms of the same element in the same

physical state.

The most common form of sulphur is S8

3 allotropes: monoclinic, rhombic, plastic

a) Rhombic sulphur – Is

stable below 96oC. The

crystals of rhombic sulphur are

diamond shaped.

b) Monoclinic sulphur –

this is stable above 96oC

.The

crystals of monoclinic sulphur

are needle shaped.

c) Plastic Sulphur – Brown and rubber. Consists of tangled chains of sulphur.

Rhombic sulphur is the stable form at room temperature. The crystal shape is shownabove. When it is heated slowly above 95.5 ºC, it is converted to monoclinic sulphur. Bothof these forms are insoluble in water but soluble in carbon disulfide, CS2.

When sulphur is heated above 113 ºC, it melts to form a pale yellow liquid, which becomesdarker and more viscous as the temperature is increased. If liquid sulphur is heated to itsboiling point of 445 ºC, and poured into cold water, so-called plastic sulphur is formed,consisting mainly of long chains of sulphur atoms, bound together by covalent bonds.




Sources and uses of the element.

• Sulphur has been known since the beginning of history, and is described in the Bible.

• Sulphur has been used by the Greeks and Romans as a fumigant and disinfectant.

Occurrence

• Sulphur is widely distributed as the free element and combined in compounds.• Sulphur is found near volcanoes, where it is formed by the reaction of sulphur dioxide

and hydrogen sulphide which are associated with the volcanoes.

• Sulphur also occurs in many metal ores, including

o gelena, PbS,

o zinc blende, ZnS,

o cinnebar, HgS,

o stibnite, Sb2S3,

o copper pyrites, Cu2S.Fe2S3, and

o iron pyrites, Fe2S.

• The important sulphate ores include

o gypsum, CaSO4, ando heavy spar, BaSO4.

Extraction

• Sulphur is separated from the minerals in its ores by heating, when the liquid sulphur

drains from the ore body. Normally, part of the sulphur in the ore is burned and the heatused to melt the remaining sulphur so that it leaches from the hot mass. This extraction

procedure called the Gill Process, and it is widely used in Sicily.

• Sulphur is extracted from underground ore bodies in the United States using the FraschProcess, where superheated water is pumped underground to melt the sulphur which is

then forces to the surface.

Uses: Sulphur is an important industrial raw material, which is used

• in the manufacture of sulphuric acid,

• in the manufacture of sulphur dioxide and sodium sulphite which are

used for bleaching straw and wood fibers, and for removing lignin

from wood pulp for the paper industry, and

• in the manufacture of organic chemicals which contain sulphur

• is a component of black gunpowder (a mixture of potassium nitrate,

KNO3, carbon, and sulphur)

• It is used in the vulcanisation of natural rubber,• as a fungicide

• as a fumigant.

• its compounds are used in the bleaching of dried fruits and for paper

products.

Reactions: Melts into an amber coloured liquid.

• Burns with a blue flame, forming sulphur dioxide: S(s) + O2(g) SO2 (g)

• Reacts with iron – A mixture of Fe & S is heated, once reaction starts heating is stopped.A red glow spreads throughout the mixture and grey FeS solid is formed: Fe + S FeS




Complete:

Sulphur is a _____________ (colour) solid and melts when heated into an

_____________ coloured liquid. Two allotropes of sulphur are _________________

sulphur which is made of needle shaped crystals and _______________ sulphur which is

made of diamond shaped crystals. When sulphur burns, it does so with a ___________

flame producing _______________________ gas. This is a pollutant gas since it is

___________________ and produces ___________ rain.

Write down the formula of:

a. Sulphur atom __________ f. sulphurous acid __________

b. Sulphur molecule __________ g. sulphuric acid __________

c. A sulfide ion __________ h. sulphur dioxide __________

d. A sulphate ion __________ pi. sulphur trioxide __________

e. A sulfite ion __________

Oxides of Sulphur

SO2 The laboratory preparation of dry sulphur dioxide by the reaction of

a) a dilute acid on a sulfite – Sodium sulfite (Na2SO3) and dilute hydrochloric acid (HCl)

Na2SO3 (s) + 2 HCl (aq) 2 NaCl (aq) + SO2 (g) + H2O (l)

1. The two are heated in a flask.

2. Sulphur dioxide (SO2) is given off

3. It is dried and collected.4. Hydrochloric acid (HCl) is a stronger acid than sulphur dioxide. So Hydrochloric acid

displaces sulphur dioxide from its salt, sodium sulfite Na2SO3

b) concentrated sulphuric acid on copper.

Copper and concentrated sulphuric acid are mixed

together and then heated. Sulphur dioxide is givenoff:

Cu (s) + 2 H2SO4 (l) CuSO4 (s) + 2H2O (l) + SO2 (g)

It is dried by passing through concentrated sulphuric

acid and collected by downward delivery as it is

denser than air.

It cannot be collected over water as sulphur dioxide is

soluble in water. When hot and concentratedsulphuric acid acts as an oxidising agent. So it reacts

with copper and concentrated sulphuric acid is

reduced to sulphur dioxide.




Physical Properties

Colourless

Choking smell

Heavier than air Soluble in water

Poisonous

Chemical properties

Dry gas is neutral to litmus, but in water forms an acidic solution, called sulphurous acid

(pH = 2) and partially dissociated into ions.

Preparation of aqueous sulphur dioxide; acidic nature of the solution (linked to acid rain).

H2O (l) + SO2 (g) H2SO3 (aq) 2 H+ (aq) + SO3-- (aq)

Sulphurous acid Sulphite ion

Test for the gas (linked to reducing action of the gas.)

1. When bubbled through potassium permanganate solution, this turns from purple to

colourless2. When bubbled through potassium dichromate solution, this turns from orange to green.

3. When bubbled through a solution containing iron (III) ions, these change to iron (II) ions.

4. It also reacts with concentrated nitric acid, and this is reduced to brown nitrogen dioxidegas.

5. Some coloured things lose colour when reduced as SO2 acts as a bleach.

Uses of sulphur dioxide.

To bleach paper

In the preparation of jams, dried fruits as it stops the growth of bacteria and moulds To make sulphuric acid.

SO3 - Acidic nature of sulphur trioxide.

Both sulphur dioxide and sulphur trioxide are chemicals that are called acidic oxides. They react

with water to form their corresponding acids- sulphurous acid and sulphuric acid. The increasingconcentration of these molecules in the atmosphere in recent years has caused the environmental

problem we know as acid rain.

SO3 (g) + H2O (l) H2SO4 (aq) sulphuric acid

Complete:

Sulphur dioxide normally acts a/n ________________ agent. But it behaves as such when thepresence of ______________. This happens because in the presence of water, the

_____________ ion is formed. When this ion acts as such, it itself is _____________ to the

_________________ ion. Sulphur dioxide changes acidified potassium dichromate from

_______________ to ________________.




Sulphuric Acid - H2SO4

The manufacture of sulphuric acid by the Contact process

The Contact Process: makes sulphur dioxide SO2; converts the sulphur dioxide into sulphur trioxide SO3 (the reversible reaction at

the heart of the process); converts the sulphur trioxide into concentrated sulphuric acid – H2SO4

Process divided into 3 stages:

1. Preparation and purification of SO2

2. Catalytic oxidation (using Vanadium

oxide catalyst) of SO2 to SO3

3. Conversion of SO2 to H2SO4

Making the sulphur dioxide - This can be made by burning sulphur

in an excess of air:

Converting the sulphur dioxide into sulphur trioxide

This is a reversible reaction, and the formation of the sulphur trioxide

is exothermic.

Converting the sulphur trioxide into sulphuric acid This can't be done by simply adding water to the sulphur trioxide - thereaction is so uncontrollable that it creates a fog of sulphuric acid.

Instead, the sulphur trioxide is first dissolved in concentrated sulphuricacid:

The product is known as fuming sulphuric aci d or oleum. This can then be reacted safely with water

to produce concentrated sulphuric acid.




Uses of sulphuric acid

To make fertilizers such as ammonium sulphate and superphosphates

In the manufacture of paints, pigments, natural and man-made fibres In the manufacture of plastics, detergents, soap, explosives, batteries, insecticides

For cleaning metals.

Properties

a) As a typical dilute acid

When dilute it reacts with metals above hydrogen in the reactivity series giving hydrogen.

Metal + Acid Salt + HydrogenZn (s) + H2SO4 (aq) Na2SO4 (aq) + H2 (g)

It reacts with metal carbonates:

Metal Carbonate + Acid Salt + Carbon dioxide + water

Na2CO3 (s) + H2SO4 (aq) Na2SO4 (aq) + CO2 (g) + H2O (l)

It reacts with bases

Base + Acid Salt + WaterNaOH (aq) + H2SO4 (aq) Na2SO4 (aq) + H2O (l)

b) When concentrated:

Concentrated sulphuric acid is not acidic. This happens as an acid becomes acidic when it isdissolved in water. Pure sulphuric acid is a poor conductor of electricity. It is a non-electrolyte

as it only consists of molecules.

hygroscopic nature;

Concentrated sulphuric acid has a great affinity (desire) for water. If some concentrated

sulphuric acid is left in a beaker, it is found that the volume increases after several days. This

happens because it absorbs water vapour from the atmosphere. Thus concentrated sulphuric acidis called hygroscopic.

dehydrating action - This means that it removes chemically bound water

It removes the chemically bound water present in hydrated copper(II) sulphate. The blue

copper(II) sulphate turns to white anhydrous copper(II) sulphate.

CuSO4.5H2O s) CuSO4 (s) + 5 H2O (l) taken by the acid

It also removes the elements hydrogen and oxygen (2:1) from compounds like sugar.

C12H22O11 (s) 12 C (s) + 11 H2O (l) taken by the acid




oxidising action - (exemplified by the reaction with copper – see notes pg. 66).

Action on chlorides and nitrates.

Many Metallic Chlorides liberate Hydrogen Chloride gas, HCl, when warmedwith concentrated Sulphuric Acid, H2SO4.

reaction of sulphuric acid with potassium nitrate can be used to produce nitricacid

• Sulphates and Hydrogensulphates

General methods of preparing salts as applied to sulphates - covered in Unit 5, Topic 5.4

Reacts with alkalis to form either a normal salt or an acid salt.

a) Acid salt: NaOH (aq) + H2SO3 (aq) NaHSO3 (aq) + H2O (l)

b) Normal salt: NaHSO3 (aq) + NaOH (aq) Na2SO3 (aq) + H2O (l)

Preparation of sodium sulphate by titration method;

See. _________________________________________

Modifying the results of the titration to prepare sodium hydrogensulphate.

Solubility

Action of heat on hydrated copper (ll) sulphate and hydrated iron (ll) sulphate. covered in Topic 9,1

Some important sulphates:

MgSO4.7H2O Epsom salts,

CaSO4.2H2O Gypsum and Plaster of Paris,

(NH4)2SO4 in fertilizers - also mentioned in Unit 5, Topic 5.4, and Unit 7, topic 7.3.

Test for SO32-

and SO42-

- covered in Unit 9, Topic 9.2




10.3 HalogensChlorine

Give the formulas of:

o Hydrochloric acid (with state symbols) _________

o Hydrogen chloride (with state symbols) _________

o Chlorine gas _________

o Chlorine molecule _________

o Chlorine atom _________

o Chloride ion _________

o Hypochlorite ion _________ (acts as a bleach)

Complete

Chlorine is a _____________________ (colour) gas. It is __________________ so it is used to

__________________ drinking water. When chlorine dissolves in water, the solution is called

__________________. This solution is __________________ (colour), is (acidic/alkaline) and

is a __________________.

Laboratory preparation of pure, dry chlorine by the oxidation of hydrochloric acid.

Concentrated hydrochloric acid is added onto solid potassium permanganate.

Hydrochloric acid is oxidized to chlorine.

2 KMnO4 (s) + 16 HCl (aq) 2 KCl (aq) + 2 MnCl2 (aq) + 8 H2O (l) + 5 Cl2 (g)

It is collected over brine, because it does not dissolve in it.If it is required dry, it is passed through water to remove the hydrogen chloride, then through

concentrated sulphuric acid to dry it, then collected, by downward delivery.

Industrial Preparation

a) Electrolysis of molten sodium chlorideb) Electrolysis of sodium chloride solution (brine)

Test for chlorine.

It bleaches damp litmus paper

Physical properties.

Greenish-yellow gas with a choking smell

Denser than air Poisonous




Soluble in water – solution formed is called chlorine water and is greenish in colour

Chemical properties

Chlorine is very reactive and forms compounds with many metals and non-metals

The reaction of chlorine with:

o WATER – chlorine in water is very acidic and a strong bleach

Cl2 (g) + H2S (g) S (s) + 2 HCl (g)

The solution is acidic due to the presence of hydrochloric acid and hypochlorous acid

O METALS E.G. IRON AND COPPER

Reacts with iron to form iron (III) chloride. Pure dry chlorine is passed

over the heated iron. The wire glows and the reaction continues without

heating. Black crystals of iron (III) chloride are formed.

2 Fe (s) + 3 Cl2 (g) 2 FeCl3 (s)

This reaction is called a direct combination reaction.

When a piece of Dutch metal (a very thin sheet of an alloy of copper and zinc) is dropped into a

gas-jar of chlorine, it reacts to from copper (II) chloride and zinc chloride.

Cu (s) + Cl2 (g) CuCl2 (g)Zn (s) + Cl2 (g) ZnCl2 (g)

o HYDROGEN – gas jars placed mouth to mouth. Reaction explosive in sunlight

H2 (g) + Cl2 (g) 2 HCl (g)

Oxidising action of chlorine - on metals and on iron (ll) chloride.

When bubbled through iron (II) chloride solution (pale green), this is oxidized to iron (III)chloride solution (yellow brown).

2 FeCl2 (aq) + Cl2 (g) 2 FeCl3 (aq)

It also oxidizes sulphite ion to the sulphate ion.

Displacement reactions of one halogen by another.

It displaces iodine from potassium iodide solution.

Cl2 (g) + 2 KI (aq) 2 KCl (aq) + I2 (aq)




Uses of chlorine

1. For the manufacture of bleaching powder and liquid bleaches,2. To bleach fabrics (e.g. linen and cotton), wood pulp and paper,

3. In the manufacture of a wide range of chloro-organic solvents, including Chloroform,

CHCl3

4. Or the direct manufacture of Hydrochloric Acid by the direct combination of its elements,

H2 + Cl2 2 HCl

5. For the extraction of Gold from its ores,

6. In the manufacture Sodium Hypochlorite (i.e. domestic bleach), disinfectants,insecticides, plastics and Hydrochloric Acid,

7. As a disinfectant used to kill bacteria in the preparation of drinking water.

8. Chlorine is also important in the manufacture of paints, aerosol propellants and plastics.

Hydrogen chloride

The laboratory preparation of dry hydrogen chloride;

Concentrated sulphuric acid is added onto sodium chloride

NaCl (s) + H2SO4 (aq) NaHSO4 (aq) + HCl (g)

The hydrogen chloride gas is dried by passing through concentrated sulphuric acid and collected

by downward delivery.

Test for the gas

o It is a clear gas (although in damp air it appears misty) and Acid to litmus

o Produces a white precipitate of silver chloride in a drop of solution of silver nitrate and

nitric acid which is help on a glass rod in the gas.

Ag+ (aq) + Cl

- (aq) AgCl (s)

Hydrogen chloride




MOST COMMON TEST

o Produces dense white fumes in the presence of ammonia as ammonium chloride forms.

HCl (g) + NH3 (g) NH4Cl (aq)

Properties.

o Denser than air

o Choking smell, irritates eyes and lungs

o Very soluble in water forming hydrochloric acid

Preparation of aqueous hydrogen chloride - using inverted funnel method

The inverted funnel arrangement if used when the gas is very soluble in water. If

glass tubing is used to dissolve the very soluble gas in water, it may be absorbed

at a greater rate than is being produced, and so water may be sucked back.

But if the inverted funnel arrangement is used, a great volume of water is needed

to fill the funnel. This lowers the level of water in the beaker and since the rim ofthe funnel is only immersed, causes the rim to be exposed. So air enters and the

water drops back from the funnel.

This is also useful when preparing solutions of sulphur dioxide and ammonia.

Reactions of dilute hydrochloric acid as a typical acid.

Metal + Acid Salt + Hydrogen

Zn (s) + 2 HCl (aq) ZnCl2 (aq) + H2 (g)

Metal Carbonate + Acid Salt + Carbon dioxide + Water

Na2CO3 (s) + 2 HCl (aq) 2 NaCl (aq) + CO2 (g) + H2O (l)

Alkali + Acid Salt + Water

NaOH (aq) + HCl (aq) NaCl (aq) + H2O (l)

Inustrial Preparation of Hydrochloric Acid

i) Reacting sodium chloride with sulphuric acid. The hydrogen chloride is then

dissolved in water to form hydrochloric acid.

2 NaCl (s) + H2SO4 (aq) Na2SO4 (s) + 2 HCl (g)

ii) Direct combination of hydrogen with chlorine. The hydrogen chloride is then

dissolved in water to form hydrochloric acid.

water

HCl




H2 (g) + Cl2 (g) 2 HCl (g)Hydrogen chloride in water and in Toluene.

In water breaks up: HCl (g) H+ (aq) + Cl

- (aq) and is acidic.

In toluene it remains covalent and does not act as an acid.

Chlorides of common metals

Preparation of sodium chloride by neutralisation,

When a base e.g. NaOH is reacted with an acid e.g. HCl, sodium chloride is the salt formed.

Magnesium chloride is found in seawater. So seawater is as a source of magnesium metal,

extracted by electrolysis.

The reaction of chlorides with conc. sulphuric acid – e.g reaction with NaCl pg. 74 notes

Revise test for halide ions in solution – see notes pg. 45

All attacked by chlorine to

form a chloride

The equation that takesplace is:

2 Fe (s) + 3Cl2 (g)

2FeCl3 (s)

To make Iron (II) chloride,iron is reacted with HCl (g)

or (aq):

Fe (s) + 2HCl (g) FeCl2 (aq) + H2 (g)

Anhydrous calcium chloride is a

deliquescent substance as it

absorbs water vapour from the

atmosphere and dissolves in it.

General methods of preparing

metallic chlorides.




Revision Questions – answer on your copybook

1. (a) Some of the substances that sulphuric acid reacts with are:

(i) magnesium (ii) copper (II) oxide (iii) potassium chloride

For each reaction, state whether concentrated or dilute acid should be used, what would

be observed and write an equation for the reaction. (12 marks)

(b) Concentrated sulphuric acid acts as an oxidising agent in its reaction with coppermetal. One of the products is sulphur dioxide gas

(i) Give an equation for the reaction and use it to explain why concentratedsulphuric acid acts as an oxidising agent. (3 marks)

(ii) Sulphur dioxide is itself a reducing agent. Briefly describe a test given by

sulphur dioxide which shows that it acts as a reducing agent. (An equation isnot required). (2 marks)

(c) Concentrated sulphuric acid acts as a dehydrating agent in its reaction with

sucrose, C12H22O11. Explain this statement and state what would be seen

during the reaction. (3 marks)

2. Sulphuric acid is manufactured by the Contact Process. In this process sulphur trioxide is

formed by passing sulphur dioxide and oxygen over a heated catalyst.

(a) Give the names of the raw materials which are used as a source of:

(i) sulphur dioxide (ii) oxygen (2 marks)

(b) What is meant by the term ‘catalyst’? (2 marks)

(c) Write an equation for the reaction of sulphur dioxide with oxygen (2 marks)

form 4 chem chapter 4

Documents