AI English Translation, Pages 176-200
Page 15.
47. AIR IS NECESSARY FOR BURNING AND RUSTING.
When some subtances are heated in the air their weights
increase. For example, if we leave a piece of iron for a few
days in a damp place it will rust and increase in weight. In
such cases a certain part of air disappears during rusting or
burning and rusting is accompanied by an increase in weight.
Lavoisier, a French scientist heated some mercury for a
few days in a retort the neck of which extends into an air
jacket converted in a trough containing mercury. He found
that mercury rose to about one-fifth of the jacket and that
the mercury in the retort became covered by a red powder
which differed from mercury in every detail. He then took a
burning piece of wood and introduced it into the jacket and
found that it was extinguished. Therefore he said that only
one fifth of the air is necessary for burning. This one
fifth of air was later called Oxygen. It is the part which
has disappeared from the air jacket and combined with the
mercury in the retort to form the red powder.
⟦line⟧
Page 14.
A I R
WHAT IS AIR ?
Is it a mixture or a compound ?
What are the gases which constitute it ?
What is the importance of each constituent for living bodies ?
⟦line⟧
44. THE CONSTITUENTS OF AIR.
Air is a mixture of different gases and not a compound. It is
a mixture of the following gases:-
1. | Oxygen | 21 %
2. | Nitrogen | 78 %
3. | Carbon Dioxide | 0.04% approximately
4. | Water vapour | variable proportions
5. | Rare gases (Argon, Neon., Krepton & Helium) | 1 % approximately
6. | Dust. |
45. AIR IS A MIXTURE.
Experiments proved that air is a mixture and not a compound
because:-
1. Every gas which is a part of air retains its physical and chemical
properties.
2. The proportions of the constituents of air are variable.
3. Its constituents can be separated easily as when liquid air is
evaporated, nitrogen is liberated first leaving Oxygen.
46. ALL THE CONSTITUENTS OF AIR ARE NECESSARY FOR LIFE.
1. Oxygen: It is necessary for respiration in both plants and animals.
2. Nitrogen: It dilutes oxygen and if only oxygen was found in the air,
the lungs would have been burnt. Nitrogen is also taken
by certain bacteria which live in the roots of some plants
and is changed into proteins, (e.g. beans roots).
3. Carbon dioxide: It is taken through the leaves of plants and changed
into starch or sugar in the presence of sunlight and
chlorophyll.
4. Water vapour: It prevents much evaporation from the bodies of
plants and animals.
5. Rare gases: They are inactive gases and are of no importance
for life.
Page 15.
47. AIR IS NECESSARY FOR BURNING AND RUSTING.
When some subtances are heated in the air their weights
increase. For example, if we leave a piece of iron for a few
days in a damp place it will rust and increase in weight. In
such cases a certain part of air disappears during rusting or
burning and rusting is accompanied by an increase in weight.
Lavoisier, a French scientist heated some mercury for a
few days in a retort the neck of which extends into an air
jacket converted in a trough containing mercury. He found
that mercury rose to about one-fifth of the jacket and that
the mercury in the retort became covered by a red powder
which differed from mercury in every detail. He then took a
burning piece of wood and introduced it into the jacket and
found that it was extinguished. Therefore he said that only
one fifth of the air is necessary for burning. This one
fifth of air was later called Oxygen. It is the part which
has disappeared from the air jacket and combined with the
mercury in the retort to form the red powder.
⟦line⟧
Page 13.
2- Decomposition or "Analysis", is a reaction in which a compound
is broken up into simpler compounds. For example,
(a) 2 H₂O ⟦line⟧> 2 H₂↑ + O₂↑
Water Catalyst hydrogen oxygen
(b) 2K Cl O₃ ⟦line⟧> 2K Cl + 3O₂
potassium Chlorate pot.Chloride oxygen
(c) Ca CO₃ ⟦line⟧> Ca O + CO₂↑
Calcium Carbonate Calcium oxide Carbon dioxide
3- Simple Replacement or "Substitution", is the reaction in which
a free element replaces another element in a compound For
example,
(a) Zn + H₂ SO₄ ⟦line⟧> Zn SO₄ + H₂↑
Zinc Sulphuric acid Zinc sulphate hydrogen
(b) Na + 2 H₂ O ⟦line⟧> 2 Na OH + H₂↑
sodium Water Sod.hydroxide hydrogen
4- Double Replacement or "Metathesis" , is the reaction in which
two compounds exchange metallic and non-metallic components to
form two new compounds. For example,
Ag NO₃ + Na Cl ⟦line⟧> Na NO₃ + Ag Cl↓
silver nitrate sod.chloride sod.nitrate silver Chloride
⟦line⟧
Page 12.
3- Balance the equation by writing Coefficients before the symbols
or formulas, if necessary, so as to give the same number of atoms
of each element on both sides of the arrow.
4- When a gas is evolved it is indicated by an arrow pointing upward
( ↗ ) . When a precipitate is formed it is indicated by an arrow
pointing downward ( ↓ ).
5- When heat is applied in a chemical reaction, it is expressed by
the sign (Θ) or (△) and is written above the arrow. If an
electric current is applied, it is expressed by the sign ( ⌿ )
and is put above the arrow. If any other catalyst is applied an
indication of it should appear with the arrow also.
N.B. 1- Subscripts in the formulas should never be changed because
that would mean an alteration in the composition of the
substance.
2- Most gaseous elements such as hydrogen, oxygen, nitrogen
and Chlorine, exist in the free (uncombined) state as
diatomic molecules. Viz : H₂, O₂, N₂, Cl₂.
43. TYPES OF CHEMICAL REACTIONS:- In general, there are four types of
chemical reactions:-
1- Direct Combination or "Synthesis" which is a chemical union of
two or more elements or compounds forming a more complex substance.
For example,
(a) H₂ + Cl₂ ⟶ sun light ⟶ 2 H Cl
hydrogen Chlorine hydrochloric acid
(b) C + O₂ ⟶ Θ ⟶ CO₂
Carbon Oxygen Carbon dioxide
(c) Ca O + H₂O ⟶ Ca (OH)₂
Calcium oxide Water Calcium hydroxide
Page 11.
40. WRITING FORMULAS: A knowledge of the valencies of the different
elements & radicals is an essential requirement for writing the formulas
of the different compounds correctly. If we know that two elements or
radicals combine to form a compound we proceed to build up its formula
according to the following steps:-
1. Represent by symbols, first the metallic part, and then the
non-metallic part, of the compound as follows:-
Na Cl, Na SO₄, Ca CO₃, Ca PO₄ .
2. Write a subscript number for each element or radical equal to
the valence of the other element or radical in the compound, enclosing
radicals in parentheses as follows:
Na₁ Cl₁, Na₂ (SO₄)₁, Ca₂ (CO₃)₂, Ca₃ (PO₄)₂
3. The subscript 1 is omitted, as are also the parentheses of
radicals whose subscript is 1. Subscripts are omitted also when the
two parts of the compound have similar subscript numbers; i.e., when
they are of the same valency. The completed formulas of the above
compounds are therefore:
NaCl, Na₂SO₄, CaCO₃, Ca₃(PO₄)₂
41. CHEMICAL EQUATIONS: A chemical equation consists of symbols and
formulas representing a complete chemical reaction. For example,
the following equation represents the reaction between Zinc and
hydrochloric acid:
⟦illegible⟧ ⟦line⟧ ⟦illegible⟧
A chemical equation tells in shorthand language what the sub-
stances which react are, and what products are formed. The two sides
of an equation are separated by an arrow. When reading a chemical
equation, the words "Yields" or "Forms" are substituted for the arrow.
42. WRITING EQUATIONS: If we are given two or more substances which will
react with each other and yield certain products under given conditions,
we may represent this chemical action by an equation as follows:
1- On the left of the arrow express by means of a symbol or a formula
each substance involved in the chemical reaction.
2- On the right of the arrow express in a similar way each product
formed.
Page 10
⟦line⟧
37. RADICALS AND THEIR VALENCE.
A radical is a group of elements which behave as a unit in chemical reactions, and which has an individual valence just like any other element. For example, (NH₄) is a radical called ammonium and is univalent. Again, in Sulphuric acid which has the formula H₂SO₄, the group (SO₄) is the sulphate radical which is divalent because it combines with two atoms of hydrogen to form (H₂SO₄). It is important to note that radicals do not exist in a free state as other compounds do.
Below is a list of different radicals with their symbols and valencies:
Radical | Symbol | Valency | Radical | Symbol | Valency
Nitrate | NO₃ | 1 | Acetate | CH₃COO | 1
Chlorate | ClO₃ | 1 | Sulphate | SO₄ | 2
Ammonium | NH₄ | 1 | Carbonate | CO₃ | 2
Hydroxide | OH | 1 | Silicate | SiO₃ | 2
Bicarbonate | HCO₃ | 1 | Phosphate | PO₄ | 3
38. CHEMICAL AFFINITY: Is the tendency of a certain element to combine with another element. For example, Oxygen has a Chemical affinity towards most elements, that is, it unites with most elements forming their Oxides.
39. CHEMICAL FORMULAS: A chemical formula represents the composition of a molecule. It is made up of one or more symbols with a Subscript which denotes the number of atoms which compose the molecule. The subscript 1 is never written. For example, the formula for the hydrogen molecule is H₂, which shows that a molecule of hydrogen contains two atoms of hydrogen. The formula for water is H₂O, which shows that a molecule of water contains or consists of two atoms of hydrogen and one atom of Oxygen. Again, the formula for sulphuric acid is H₂ SO₄, i.e. one molecule of sulphuric acid is composed of two atoms of hydrogen, one atom of sulphur and four atoms of oxygen.
N.B.1. The formula of a compound must not be changed at all.
2. A number written before the formula indicates the number of molecules of that element or compound, and if multiplied by the number of atoms, it gives the total atoms of each element. For example,
2 H₂SO₄ means 2 molecules of sulphuric acid; i.e. four atoms of hydrogen, two atoms of sulphur and eight atoms of oxygen.
Page 22
4- Amphoteric oxides:- Are those oxides which possess the proper-
ties of both acidic and basic Oxides. They combine with both
acids and bases to form salts.
Al2 O3 + 6H Cl ⟦line⟧→ 2 Al Cl3 + 3H2 O
Aluminium oxide hydrochloric Aluminium chloride
amphoteric oxide acid salt water
Al2 O3 + 2 Na OH ⟦line⟧→ 2 Na Al O2 + H2 O
Aluminium oxide Sod.hydroxide Sod. Aluminate
base salt water
Examples:- Zinc oxide (Zn O), Aluminium oxide (Al2O3), Lead
Monoxide (Pb O), Stannous oxide (Sn O).
5- Peroxides:- These are usually the oxides of metals containing
a greater percentage of oxygen than their basic oxides. They give
off oxygen on heating.
θ
2 Ba O2 ⟦line⟧→ 2 Ba O + O2 ↑
Barium peroxide Barium oxide oxygen
Examples:- Barium peroxide (Ba O2), Sodium peroxide (Na2 O2),
Zinc peroxide (Zn O2) & hydrogen peroxide (H2 O2).
A C I D S
59. DEFINITION: - An acid is a hydrogen compound whose hydrogen may
be replaced by a metal and whose water solution changes the
colour of litmus from blue to red.
Many compounds such as sugar and alcohol, contain hydrogen, but
are not acids, because their hydrogen atoms cannot be replaced
by a metal. The hydrogen of the acid is always accompanied by
a non-metallic element such as Cl,S or by a radical such as (N O3),
(SO4) and (P O4).
Page 23
60. PREPARATION OF ACIDS - There are two common methods for the
preparation of acids:
1- By the action of acidic oxides (acid anhydride) with water e.g.
S O3 + H2 O ⟦line⟧> H2 S O4
C O2 + H2 O ⟦line⟧> H2 C O3
2- By the action of sulphuric acid with a salt of the required
acid e.g.
H2 SO4 + 2 Na Cl ⟦line⟧> 2 H Cl + Na2 SO4
61. PROPERTIES OF ACIDS:-
1- Acids taste sour.
2- They change ⟦litmus⟧ colour from blue to red.
3- All acids contain hydrogen which ⟦is⟧ replaceable by active
metals e.g.
Zn + 2H Cl ⟦line⟧> Zn Cl2 + H2
4- They react with marble (Ca CO3) causing effervescence and
evolution of CO2.
2H Cl + Ca CO3 ⟦line⟧> Ca Cl2 + C O2 + H2 O
5- Acids react with bases forming salt and water.
H Cl + Na O H ⟦line⟧> Na Cl + H2 O
62. NAMING OF ACIDS:-
a- In case the acids do not contain oxygen i.e. when they are only
composed of ⟦hydrogen and a non-metal⟧ they are named by using the
full name of the non-metal with the prefix hydro - and ending
with - ic. Examples hydrochloric acid ( H Cl), hydrosulphuric acid
H2 S.
b- In case they contain enough oxygen, they are named by using the name
of non-metal ending with - ic. Examples, sulphuric acid ( H2 SO4 ),
carbonic acid ( H2CO3 ) and nitric acid ( H N O3 ).
c- When the acids contain one less atom of oxygen, they are named
by using the name of the non-metal ending with - ous. Examples,
sulphurous acid ( H2 SO3 ) and nitrous acid ( H N O2 )
Page 24
B A S E S
63. DEFINITION:- A base is a compound of a metallic element or a radical
with one or more hydroxyl ( O H) groups. The water solution of a base
change the colour of ⟦litmus⟧ from red to blue.
64. PREPARATION OF BASES:-
1- By the action of basic oxides with water:-
Ca O + H2 O ⟦line⟧> Ca ( O H)2
Mg O + H2 O ⟦line⟧> Mg ( O H)2
2- By the action between a base and a salt.
Na2 CO3 + Ca ( O H)2 ⟦line⟧> 2 Na O H + Ca CO3 ↓
Fe Cl3 + Na OH ⟦line⟧> 3 Na Cl + Fe ( O H)3 ↓
3- By the action of an active metal and water:
2 Na + H2 O ⟦line⟧> 2 Na OH + H2 ↑
65. PROPERTIES OF BASES.-
1- In general bases have a bitter taste.
2- Bases turn red litmus into blue.
3- Bases contain hydroxyl ( O H) group.
4- Bases do not react with marble.
5- Bases ⟦neutralize⟧ acids forming salt and water.
66. NAMING OF BASES: Bases are named ⟦by placing⟧ the name of the metal
before the word " hydroxide ".
Examples: Sodium hydroxide ( Na OH), Calcium hydroxide (Ca ( O H)2 ).
Strong soluble bases such as ( Na OH) and ( K O H) are often called
alkalies.
Page 25
( SALTS )
67. DEFINITION:- A "salt" is a compound consisting of a metal or a metallic
radical combined with a non-metal or an acid radical. In other words,
a salt is an acid the hydrogen of which is replaced by a metal or a
radical. The term salt, as commonly used, refers to sodium chloride,
but in chemistry salt is the general name of a class of compounds which
resemble Sod. Chloride.
68. PREPARATION OF SALTS:- Salts are prepared by a variety of methods.
1- Neutralization:- Neutralization is the reaction between an acid and
a base, forming salt and water. For example:
Na OH + HCl ⟦line⟧> NaCl + H₂O
In making NaCl by this method a small quantity of NaOH solution is
placed in a dish with a piece of blue litmus paper. Hydrochloric acid
is then added drop by drop until the litmus paper just turns red. If
this neutral solution is now evaporated to dryness, a white deposit
of (NaCl) remains, and may be identified by its salty taste.
2- Action of an Acid on a Metal:-
Zn + H₂SO₄ ⟦line⟧> ZnSO₄ + H₂
3- Action of an Acid on metallic oxides:
CaO + 2 HCl ⟦line⟧> CaCl₂ + H₂O
4- Action of an Acid on the Salt of a More Volatile Acid
H₂SO₄ + 2 NaCl ⟦line⟧> Na₂SO₄ + 2 HCl
5- Double Replacement Resulting in the Formation of an Insoluble product:
BaCl₂ + Na₂SO₄ ⟦line⟧> 2 NaCl + BaSO₄
6- Direct Union of the Elements:
Zn + S ⟦line⟧> ZnS
7- Union of a metallic oxide and a Non-Metallic Oxide
CaO + SiO₂ ⟦line⟧> CaSiO₃
Page 26
69. PROPERTIES OF SALTS: Salts vary widely in characteristics.
As a general rule, salts are white, crystalline solids with a salty
taste. They are usually soluble in water, and Neutral to litmus
paper. Among the many exceptions to the above, are copper sulphate,
which is blue; calcium carbonate (marble) which is insoluble in
water and sodium carbonate which in solution reacts basic to litmus,
owing to hydrolysis.
70. TYPES OF SALTS.
1- An "acidic salt" is one in which only part of the hydrogen of
the acid has been replaced by a metal. Thus Sodium acid carbonate,
or sodium bicarbonate (Na HCO₃), and sodium acid phosphate
(Na H₂ PO₄) are acid salts.
2- A "basic salt" is one which contains one or more hydroxyl (OH)
radicals. Thus bismuth subnitrate Bi (OH)₂ NO₃ is a basic salt used
in medicine.
3- A "Normal salt" is one which contains only a metal or a
metallic radical, combined with a non-metal or an acidic radical.
It contains neither hydrogen replaceable by a metal nor a hydroxyl
radical. Thus Ca CO₃ & NaCl are normal salts.
4- A double salt is one which contains two metals combined with one
acidic radical. Thus common alum is a double sulphate of potassium
and aluminum, having the formula K₂ SO₄ . Al₂ (SO₄)₃ . 24 H₂ O
or K Al (SO₄)₂ . 12 H₂ O .
71. NAMING SALTS: The name of a salt consists of two parts, the name
of the metal and the name derived from the acid. For example :
Acids of Chlorine | Formulas | Sodium Salts of the acids | Formulas
Hydrochloric acid | H Cl | Sod. Chloride | Na Cl
Chlorous acid | H Cl O₂ | Sod. Chlorite | Na Cl O₂
Chloric acid | H Cl O₃ | Sod. Chlorate | Na Cl O₃
Page 27
( H Y D R O G E N )
72. OCCURRENCE Hydrogen is not as abundant as oxygen. It occurs both
free and in the combined state in nature. In the combined state it
occurs nearly everywhere, but in the free state, it occurs in natural
gas and in volcanic gases. Traces of hydrogen are found in the lower
strata of the earth's atmosphere and gradually its quantity increases
at high altitudes. Hydrogen is known to occur abundantly in the
sun's atmosphere.
In the combined state hydrogen constitutes about 1% of the earth crust
and one ninth of the weight of water. It occurs in all acids, in
animal and vegetable matter, such as butter, starch, sugar, in
hydrocarbons such as kerosene, gasoline, etc..
73. METHODS OF PREPARATION .-
1- LABORATORY METHODS.
a) by the action of certain metals on non oxidizing acids.
Metals such as zinc and iron react with certain dilute acids,
notably hydrochloric acid and sulphuric acid.
Zinc is put in a flask closed by a rubber stopper, through
which a thistle tube extends to the bottom of the flask, and a
delivery tube also extends to a trough containing water, over which
a large test tube filled with water is inverted. The dilute acid is
poured through the thistle tube until it covers its lower end.
Zinc replaces the hydrogen of the acid.
thistle tube
delivery tube
hydrogen gas
test tube
water
trough
HCl
Zn
Zn + 2H Cl ⟦line⟧> Zn Cl₂ + H₂
Fig. 5
Page 28
and liberates this hydrogen as a gas, which passes through the
delivery tube and is collected by an upward displacement of water
at the same time forming a new salt compound called zinc chloride.
Zn + 2 H Cl ⟦line⟧> Zn Cl₂ + H₂
Fe + H₂ SO₄ ⟦line⟧> Fe SO₄ + H₂
dil.
Ag + H Cl ⟦line⟧> no reaction
b- By the action of certain metals on water:-
Various active metals (above hydrogen) react with water under
certain conditions liberating hydrogen and forming either a hydro-
xide or an oxide of the metal as follows:-
1. With cold water: as potassium, sodium & calcium
2 Na + H₂ O ⟦line⟧> 2 Na OH + H₂ vigorously
sodium water sodium hydro-
xide
Ca + 2 H₂ O ⟦line⟧> Ca (OH)₂ + H₂ slowly
calcium + water calcium hydro-
xide
2. With hot water: as Magnesium, using Na OH as a catalyst.
Mg + 2H₂ O ⟦line⟧> Mg (OH)₂ + H₂ slowly
Na OH
magnesium water Magnesium hydro-
xide
3. With steam of water: as red hot iron
3 Fe + 4 H₂ O ⟦line⟧> Fe₃ O₄ + 4 H2 Rapid
iron water magnetic oxide hydrogen
Metals below hydrogen do not react with water
Cu + H₂ O ⟦line⟧> no reaction
Note: The above reactions demonstrate the order of activity
of metals.
Page 29
( REPLACEMENT SERIES )
1 | Potassium | K ) | Highest
2 | Sodium | Na ) | activity
3 | Calcium | Ca ) | decreasing
4 | Magnesium | Mg ) | to
5 | Aluminum | Al ) |
6 | Zinc | Zn ) |
7 | Iron | Fe ) |
8 | Nickle | Ni ) |
9 | Tin | Sn ) |
10 | Lead | Pb ) |
11 | HYDROGEN | H ) | lowest
12 | Copper | Cu ) | activity
13 | Mercury | Mg ) |
14 | Silver | Ag ) |
15 | Platinum | Pt ) |
16 | Gold | Au ) |
Note: metals above hydrogen in the replacement series replace it from
dilute acids, while metals below hydrogen do not replace it
from acids.
II. COMMERCIAL METHODS:-
a- By electrolysis of water.- When an electric current is passed
through acidified water, hydrogen is liberated at the cathode.
b- By the action of Hot Coke on steam:-
When steam is passed over white - hot coke (carbon), a mixture of
hydrogen and carbon monoxide gas is formed which is called
" water gas ".
H₂ O + C ⟦line⟧> CO + H₂
When the mixture of both gases is cooled to a very low temperature,
the CO gas changes to a solid, leaving pure hydrogen. In other
cases, when the mixture of both hydrogen and carbon monoxide
gases is mixed with more steam and passed over a catalyst,
(divided Fe), CO will be changed into CO₂
CO + H₂ O + H₂ ⟦line⟧> C O₂ + 2 H₂
Then C O₂ + H₂ are treated with water at a pressure of 3o atmos-
pheres when C O₂ dissolves leaving H₂
Page 30
74. PROPERTIES OF HYDROGEN:
a- Physical Properties:
1. It is a gas under ordinary conditions.
2. It is colourless, odourless & tasteless gas.
3. It is the lightest gas known, being 14.5 times lighter than air.
4. It is very slightly soluble in water.
5. It is absorbed in large volumes by the metals palladium
and platinum accompanied by the liberation of much heat.
b- Chemical Properties:
1. Hydrogen does not support combustion; it burns with a pale
flame. When it is mixed with air or oxygen it explodes at
kindling temperature.
2 H₂ + O₂ ⟦line⟧> 2 H₂ O
2. It is not active at ordinary temperature.
3. It combines directly with other elements at high temperatures
& sometimes it combines on mere exposure to light.
H₂ + Cl₂ ⟦line⟧> 2 H Cl
Hydrogen Chlorine hydrogen chloride
200 atm.
3 H₂ + N₂ ⟦line⟧ 2 N H₃
Fe + θ
Hydrogen nitrogen ammonia
H₂ + S ⟦line⟧> H₂ S
Hydrogen sulphur hydrogen sulphide
H₂ + Ca ⟦line⟧> Ca H₂
Hydrogen Calcium Calcium hydride
4. It is a powerful reducing agent. It removes oxygen from
so many of its compounds.
75. REDUCTION:- Is the process of removing oxygen from a
compound. A substance which can effect such a removal of
oxygen is called a " Reducing agent ".
Page 31
To prove that hydrogen is a reducing agent, we pass the dry
gas (H2) over heated copper oxide as in the figure below.
drying tube
containing CaCl2
H2
CuO
drops of water
HCl
Zn
Preparation of Hydrogen
Fig. 6
The hydrogen combines with the oxygen present in the oxide,
forming water, the residue left behind in the tube is metallic
copper. Whenever reduction takes place, it is always accompa-
nied by oxidation, as can be observed by examining the equation
for this reaction:-
Cu O + H2 ⟦line⟧> Cu + H2 O
copper oxide hydrogen copper water
substance reduced reducing agent,
also oxidizing also substance
agent oxidized
76. TEST FOR HYDROGEN: Hydrogen may be identified by one chemical
test:- When hydrogen burns, the only product formed is water.
77. USES OF HYDROGEN:- Hydrogen is used:
1- To obtain a very high temperature, for welding metals.
2- For filling balloons and airships, but owing to its great
combustibility it is often substituted by helium (He).
3- For hydrogination:- Many liquid oils and fats, such as cotton
seed oil & coconut oil have disagreeable odours & tastes & can
not in their simple state be used for cooking. They are con-
verted into palatable solid fats fit for cooking, by passing
hydrogen in the presence of powdered nickel as a catalyst.
The product is called VEGETALINE.
Page 32
4- For the preparation of ammonia by Habber process.
5- It is used as a reducing agent.
6- It is a valuable constituent of some fuel gases such as
water gas and producer gas.
⟦line⟧
- 33 -
W A T E R
78. OCCURRENCE. ⟦Water⟧ is ⟦present⟧ in nature, and it occupies about 3/4 of
the earth's surface. It is also present in many salts and animal and
vegetable bodies. For example, lean meat is about 60% water, while
tomatoes are about 95% water. The human body contains about 70%
water.
79. FORMATION. Being abundant in nature, water is not usually prepared
from other materials. However, it is a product of many chemical re-
⟦actions⟧ some of which are:
1. Direct union of oxygen and hydrogen by an electric spark.
2 H2 + O ⟦line⟧> 2 H2O.
2. Oxidation of a compound of hydrogen.
CH4 + 2O2 ⟦line⟧> CO2 + 2 H2O
3. Reduction of an oxide by hydrogen.
CuO + H2 ⟦line⟧> Cu + H2O
4. Neutralization of acids and bases.
NaOH + HCl ⟦line⟧> Na Cl + H2O
80. PROPERTIES.
a- Physical Properties:
1. Water is liquid at ordinary temperature. It is tasteless and
odourless. It has no colour when in thin layers, but it acquires
a bluish tinge when it is observed through great thickness.
2. Water freezes at 0°C (32°F), and boils at 100°C (212°F).
3. Its greatest density, namely 1, (i.e. 1cc weighs 1 gm) is reached
<del>at 4 degree centigrade.</del>
4. It dissolves almost all substances to some extent, and may there-
fore be considered as a universal solvent. The pleasant taste of
drinking water is due to dissolved air and minerals.
5. Water when pure, does not conduct electricity.
b- Chemical Properties:
1. Water is extremely stable.
2. It reacts with various active metals such as Na, Ca, Fe, with
formation of hydr⟦o⟧gen.
3. It is decomposed by an electric current into hydrogen and oxygen.
4. It combines with certain metallic oxides forming bases:
Ca O + H2O ⟦line⟧> Ca (OH)2
Calcium oxide + water Calcium hydroxide
- 34 -
5. It combines with certain non-metallic oxides forming acids.
C O₂ + H₂O ⟦line⟧> H₂C O₃
Carbon dioxide + water Carbonic acid
6. Water reacts with certain salts, forming both an acid and a
base. This process is called "hydrolysis".
Al₂(SO₄)₃ + 6 H₂O ⟦line⟧> 2 Al(OH)₃ + 3 H₂SO₄
⟦Aluminium sulphate⟧ + water Aluminium + Sulphuric
hydroxide acid
7. Water combines with some compounds when they crystallize from
solution, forming hydrates, and this water is called water of
crystallization. For example:
Cu SO₄ + 5 H₂O ⟦line⟧> Cu SO₄.5H₂O
⟦unhydrous⟧ copper sulphate Hydrated crystallized
plus water copper sulphate
8. Water acts as a catalyst. Many chemical reactions cannot
take place unless there is some moisture present, as for
example, rusting of iron.
81. WATER IS A COMPOUND. Water is a compound of oxygen and hydrogen.
in the ratio of 8:1 by weight and 1:2 by volume. One of the first
steps in the study of a chemical compound is to learn its composi-
tion, that is what elements it contains, and the exact amount of
each. There are two methods of obtaining this information.
1. Analysis. On passing an electric current in an acid water in
a voltametre (Hoffman apparatus), we get hydrogen at the Cathode
and oxygen at the anode. See pages 18 and 19.
2. Synthesis. On passing a spark through a mixture of definite
quantities of oxygen and hydrogen in an eudiometer, an explosion
occurs and drops of water form on the inner surface of the tube.
Spark wires connected to
gap induction coil
Mercury
Eudiometer
- 35 -
82. WATER CYCLE IN NATURE. Water has the following cycle in nature:
1. Water evaporates from oceans and seas.
2. After evaporation it condenses and forms clouds.
3. Clouds change into rain.
4. Rain falls on the earth's surface dissolving some salts found
on its crust. Rain water then passes down through the soil
until it meets a solid layer where it collects. When sufficiently
large quantities of water are collected in this way, water is
again forced up to the earth's surface forming springs.
5. Waters from Springs and Brooks flow and meet together to form a
river. This river flows into the sea and thus the cycle is
repeated.
83. HARDNESS OF WATER. Hard water is that water which does not lather
with soap, because of the presence of SOLUBLE calcium or magnesium
salt in it which form an insoluble precipitate with soap.
Ca Cl₂ + 2 NaC₁₇H₃₅CO₂ ⟦line⟧→ Ca(H₁₇H₃₅CO₂)₂ + 2 NaCl
Sod.Stearate Calcium Stearate
soluble soap insoluble soap
Hardness is of two kinds:
a- Temporary Hardness: Is the hardness caused by the presence of
the bicarbonate of either Calcium or Magnesium (Ca(HCO₃)₂, or
Mg(HCO₃)₂). These are unstable salts, i.e. they easily
decompose on heating forming the insoluble carbonates. There-
fore this hardness can be got rid of by boiling the hard water,
as is represented by the following equations:
Ca(HCO₃)₂ ⟦line⟧→ CaCO₃↓ + CO₂↑ + H₂O
Ca.bicarbonate Calcium Carbon Water
Carbonate dioxide
Mg(HCO₃)₂ ⟦line⟧→ MgCO₃↓ + CO₂ ↑ + H₂O
Mg. bicarbonate Mg.carbonate Carbon Water
dioxide
We can also get rid of temporary hardness by adding lime water
that is calcium hydroxide ( Ca(OH)₂), or washing soda, i.e., sodium
carbonate (Na₂CO₃) as follows:
Ca(HCO₃)₂ + Ca(OH)₂ ⟦line⟧→ 2 CaCO₃↓ + 2 H₂O
Ca.Bicarbonate Ca.Hydroxide Ca.Carbonate Water
Ca(HCO₃)₂ + Na₂CO₃ ⟦line⟧→ CaCO₃ ↓ + 2 NaHCO₃
Ca.Bicarbonate Sod.Carbonate Ca.Carbonate Sod.Bicarbonate
The precipitate of calcium carbonate or Magnesium carbonate can
be removed by filtration or decantation.
- 36 -
b- Permanent Hardness: Is that hardness due to the presence of
soluble salts of Mg and Ca in water. These salts do not decompose
on heating. They are: Calcium sulphate (CaSO₄), Calcium chloride
(CaCl₂), Magnesium sulphate (MgSO₄) and Magnesium Chloride (MgCl₂).
In other words, they are Sulphate and Chloride salts of Magnesium
and Calcium.
Permanent hardness is removed by adding washing soda (Na₂CO₃)
as follows:
CaSO₄ + Na₂CO₃ ----------> Na₂SO₄ + CaCO₃
Calcium Sod. Sod. Cal.
sulphate Carbonate Sulphate Carbonate
MgCl₂ + Na₂CO₃ ----------> 2 NaCl + Mg CO₃
Magnesium Sodium Sodium Magnesium
chlordie Carbonate Chloride Carbonate
Sodium Chlordie and Sodium sulphate remain soluble and have no
action on soap lather.
⟦line⟧
k.
- 37 -
THE HALOGENS
84. NOMENCIATURE
The halogens refer to the four elements fluorine, chlorine, bromine,
and iodine. These four elements can combine with metals to form salts
such as common salt (NaCl) and hence the word halogen (meaning salt-
former) is given to this group of elements. These four elements are
grouped as one family because they resemble each other in properties
and in their chemical compounds. We shall choose the chief member of
this family, namely, Chlorine for our study as representative for the
others.
CHLORINE
85.
85. OCCURRENCE: This element is not present in nature in the free state
due to its great chemical activity. Therefore it exists in nature in
the combined form. The common compound of it is sodium chloride (NaCl)
which is common salt. Other Chlorides exist in nature such as those of
K, Mg and other elements.
86. PREPARATION:
Laboratory Methods
By oxidation of hydrochloric acid with an oxidizing agent such
as manganes dioxide:
4HCl + MnO₂ ⟦line⟧> MnCl₂ + 2H₂O + Cl₂
The apparatus commonly used for this preparation is illustrated
in the following diagram.
HCl
A
B
C
D
MnO₂
↓ Cl₂
Water
Sulphuric - acid
Fig. 7
- 38 -
Flask A contains MnO₂ to which is added concentrate ⟦...⟧ through a
thistle tube.
The Chlorine gas which is librated in flask A is passed through the
connecting tube to bottle B. This bottle contains water to absorb any
gaseous (HCl) which might escape mixed with the librated chlorine.
Chlorine gas then passes through a 2nd connecting tube to bottle C which
contains concentrated H₂SO₄ (to absorb moisture). The dry chlorine gas is
lastly collected by the downward displacement of air. Chlorine gas, unlike
oxygen and hydrogen, cannot be collected over water because it is soluble
in it.
87. PROPERTIES:
(a) Physical properties:-
1- It is a greenish yellow gas.
2- It has a strong irritating odour and when inhaled it attacks
the delicate membranes of the nose, thorat & lungs.
3- It is extremely poisonous.
4- It is about 2½ times as heavy as air.
5- It is somewhat soluble in water.
6- It is liquified easily by pressure alone at room temperature.
(b) Chemical properties:-
1- It is extremely active.
2- It combines directly with many elements forming chlorides:
a) It combines with hydrogen:
Cl₂ + H₂ ⎯⎯sun light⎯→ 2HCl
b) It combines with metals such as heated Sodium:
⟦...⟧
Cl₂ + 2Na ⎯⟦line⟧→ 2Na Cl
c) It combines with phosphorous or sulphur
5Cl₂ + 2P ⎯⟦line⟧→ 2P Cl5 Phosphorus Penta chloride
2Cl₂ + 2S ⎯⟦line⟧→ S₂ Cl₄ Sulphur chloride
3- It reacts with hydrocarbons (compounds of carbon & hydrogen),
replacing part or all of the hydrogen
CH₄ + 3Cl₂ ⎯⟦line⟧→ Ch Cl₃ + 3H Cl
Methane Chloroform
CH₄ + 4Cl₂ ⎯⟦line⟧→ C Cl₄ + 4HCl
Carbon tetrachloride
4- It acts as a bleaching agent in the presence of moisture.
This property is explained by the following equation:
Cl₂ + H₂O ⎯⟦line⟧→ 2HCl + O
The nascent oxygen which is thus liberated oxidizes the colouring
materials & bleaches it.
Chlorine is also used according to the same principle for killing
Bacteria in the process of the purification of water.
- 39 -
5- Action of Chlorine on alkalies
a) with diluted & cold alkali it forms hypo
chloride & water: -
Cl₂ + 2NaOH ⟦line⟧ NaCl+Na OCl + H₂
b) with concentrated & hot alkali it forms cholorate & chloride
& water:-
3Cl₂ + 6NaOH ⟦line⟧ 5NaCl + NaClO₃ + 3H₂O
88. USES:
1- It was used in the 1st world war as a poisonous gas.
2- It is ued in the purification of water.
3- It is used in the bleaching of coloured materials.
4- It is used for the preparation of bleaching powder, carbon
tetra-chloride, chloroform and other compounds.
89. TEST:
It is tested by exposing to it a filter paper moistured with a
solution of potassium iodide and starch. In such a case a blue
colouration indicates the presence of chlorine
Cl₂ + 2KI ⟦line⟧ 2KCl + I₂
I₂ + starch ⟦line⟧ blue colour.
⟦line⟧