C22 Non-metals

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Chapter 22: Non-metals
Chapter 22: Non-metals
Learning Outcomes
You should be able to:
• Describe the physical and chemical properties of
non – metals.
• Describe the industrial preparation of chlorine,
sulphuric acid and ammonia.
• List the uses of the non – metals: carbon, sulphur,
phosphorus, chlorine, nitrogen, silicon and their
compounds.
Chapter 22: Non-metals
H
Semi-metal
Metals
Non-metals
C N
Non-metals like Hydrogen (H), carbon (C), Nitrogen
(N) are found on the right side of the Periodic Table.
Chapter 22: Non-metals
Differences between metals and non-metals
Metals
Non-Metals
Malleable and ductile
Brittle, neither ductile nor
malleable
Good conductors of
electricity and heat
Poor conductors of heat and
electricity except graphite
Lustrous and can be
polished
Non-lustrous and cannot be
polished, except graphite and
iodine which are lustrous nonmetals
Solids at room
temperature, except
mercury
May be solids, liquids or gases at
room temperature
Chapter 22: Non-metals
Differences between metals and non-metals
Metals
Non-Metals
Strong, tough and have
high tensile strength,
except mercury and zinc
Not strong and have low tensile
strength, except diamond and
carbon fibre
Hard and have high
density, except sodium
and potassium
Generally soft and have low
density, except diamond
High melting and boiling
points
Low melting and boiling points,
except diamond and graphite
Chapter 22: Non-metals
Hydrogen (H)
Mainly occurs in a combined state in compounds
such as water, acids and many organic substances.
Elemental hydrogen exists as diatomic molecules, H2,
which has the following properties:
•Colourless, odourless and neutral gas
•Non-conductor of electricity
•Low melting point (–259 °C) and low boiling point
(–253 °C)
Chapter 22: Non-metals
Chlorine (Cl)
Highly reactive so it never occurs in the uncombined
form in nature, mainly occurs as sodium chloride or
rock salt
Elemental chlorine exists as diatomic molecules, Cl2,
which has the following properties:
• Greenish-yellow, poisonous gas
• Non-conductor of electricity
• Denser than air
• Low melting point (–101 °C) and low boiling point (–35 °C)
Chapter 22: Non-metals
Oxygen (O)
Nearly half the mass of the Earth’s crust comprises
oxygen in a combined state in compounds such as
water, silicates, oxides and salts. Elemental form
exists in the air, forming 21% of air by volume.
Elemental oxygen exists mainly as diatomic
molecules, O2, which has the following properties:
• Colourless, odourless and neutral gas
• Non-conductor of electricity
• Low melting point (–218 °C) and low boiling point
(–183 °C)
Chapter 22: Non-metals
Carbon (C)
Found in the form of diamond (India, South Africa) and
graphite (Sri Lanka), main constituent of numerous
naturally occurring compounds such as coal, mineral
oils, carbonates, organic matter and carbon dioxide gas.
Diamond
• Colourless, transparent and has a very
high refractive index
• Hardest known natural substance
• Non-conductor of electricity
• Good thermal conductor
• Very high melting point (3550 °C)
• Very high boiling point (4827 °C)
Graphite
• Black
• Soft
• Good electrical conductor
• Very high melting point (3652 °C)
• Very high boiling point (4200 °C)
Chapter 22: Non-metals
Sulphur (S)
Exists as natural deposits of elemental or native sulphur,
compounds such as sulphur dioxide, zinc blende, pyrite
and gypsum. Present as hydrogen sulphide in petroleum
gases.
• Light yellow powdery solid
• Non-conductor of electricity
• Allotropes – rhombic and monoclinic sulphur
• Rhombic sulphur has a melting point of 113 °C and
boiling point of 445 °C
Chapter 22: Non-metals
Nitrogen (N)
Occurs combined in compounds such as sodium nitrate,
calcium nitrate and ammonium sulphate and as an
important constituent of protein. Exists as elements in
79% of the air by volume.
Elemental nitrogen exists as diatomic molecules, N2,
which has the following properties:
• Colourless, odourless and neutral gas
• Non-conductor of electricity
• Low melting point (–210 °C)
• Low boiling point (–196 °C)
Chapter 22: Non-metals
Quick Check 1
List the differences between metals and non-metals.
Solution
Chapter 22: Non-metals
Solution to Quick Check 1
Metals
Non-Metals
Malleable and ductile
Brittle, neither ductile nor malleable
Good conductors of electricity and heat
Poor conductors of heat and electricity except graphite
Lustrous and can be polished
Non-lustrous and cannot be polished, except graphite
and Iodine which is lustrous non-metals
Solids at room temperature, except mercury
May be solids, liquids or gases at room temperature
Strong, tough and have high tensile strength,
except mercury and zinc
Not strong and have low tensile strength, except
diamond and carbon fibre
Hard and have high density, except sodium
and potassium
Generally soft and have low density, except diamond
High melting and boiling points
Low melting and boiling points, except diamond and
graphite
Return
Chapter 22: Non-metals
Apart from carbon, other non-metals like
oxygen, nitrogen and sulphur have
allotropes as well.
Diatomic
oxygen (O2)
Triatomic
oxygen (O3)
Sulphur has 2 allotropes : rhombic and monoclinic sulphur. Rhombic
sulphur changes to monoclinic sulphur and vice versa at temperatures
above 96 oC and below 96 oC respectively.
Rhombic sulphur
Monoclinic sulphur
Chapter 22: Non-metals
Metals
Non-Metals
Have 1–3 electrons in the outermost
shell
Have 4–8 electrons in the outermost
shell
Lose valence electron(s) to form
cations
Gain electron(s) to form anions
or share valence electrons to form
covalent molecules
Electropositive
Electronegative
Lose electrons in the valence shell
(oxidised) and make good reducing
agents
Gain electrons from other elements
(reduced) and make good oxidising
agents
Cationic metals are discharged at the
cathode during electrolysis
Anionic non-metals are discharged at
the anode during electrolysis
Chapter 22: Non-metals
Metals
Non-Metals
Many metals displace hydrogen
from dilute acids
Do not react with dilute acids
and do not displace hydrogen
from dilute acids
Form chlorides which are
electrolytes but non-volatile
Form covalent chlorides which
are non-electrolytes but volatile
Do not combine with hydrogen,
except the reactive elemental metals
which form metal hydrides
React with hydrogen to form
stable covalent hydrides
Form basic oxides, except Cr2O3
(acidic), and Al, Zn, Pb (amphoteric)
Form acidic or neutral oxides
Chapter 22: Non-metals
Hydrogen:
Carbon:
In the presence of
insufficient oxygen,
carbon monoxide is
formed instead.
2H2(g) + O2(g) → 2H2O(g)
C(s) + O2(g) → CO2(g)
Colourless,
odourless gas and
an acidic oxide
Colourless,
stable liquid
Chapter 22: Non-metals
2Cl2(g) + O2(g) → 2Cl2O(g)
Chlorine
Anhydride of hypochlorous
acid. It is an orange gas.
Cl2(g) + 2O2(g) → 2ClO2(g)
Reddish yellow gas, a
useful oxidising agent.
The chloride oxides are acidic and
highly unstable, reacts with alkalis to
form salt.
Chapter 22: Non-metals
Nitrogen
N2(g) + O2(g) → 2NO (g)
2NO(g) + O2(g) → 2NO2(g)
Reddish brown toxic gas, which has a
sharp biting odour and is an air pollutant.
Sulphur
S(s) + O2(g) → SO2(g)
Acidic oxide, colourless gas with a
pungent smell that dissolves in
water to form acid.
Colourless gas
and a toxic air
pollutant.
Chapter 22: Non-metals
Reaction with metals are always a redox reaction where
the non-metal is the oxidising agent (electron acceptor)
and the metal is the reducing agent (electron donor).
Hydrogen
H2(g) + 2Na(s) → 2NaH2(s)
Hydrogen + Alkali metals → Metal hydrides
Nitrogen
N2(g) + 3Ca(s) → Ca3N2(s)
Nitrogen + Reactive metals → Metal nitrides
Sulphur
S(S) + Zn(s) → ZnS(s)
Sulphur + Metals → Metal sulphides
Chapter 22: Non-metals
Chlorine
Chlorine + Metals → Metal chlorides
3Cl2(g) + 2Al(s) → 2AlCl3(s)
Oxygen + Metals → Metal oxides
Oxygen
O2(g) + 2Ca(s) → 2CaO(s)
3O2(g) + 4Al(s) → 2Al2O3(s)
Aluminium oxide is amphoteric and forms an
impervious layer on the aluminium metal,
protecting it from corrosion.
Chapter 22: Non-metals
Oxidising power increases
Electronegativity increases
Oxidising power increases
Electronegativity increases
Semi-metal
Metals
Non-metals
Nitrogen, oxygen, bromine, chlorine and
fluorine are all good oxidising agents
with fluorine being the strongest.
Chapter 22: Non-metals
Across the Periodic Table, the atomic radius decreases, ionisation
energy increases, and thus the electronegativity increases. The increase
in electronegativity also reflects an increase in oxidising power.
(most
(least
Chapter 22: Non-metals
A more reactive non-metal would be able to displace a less reactive nonmetal from its salts in aqueous solutions. For example, chlorine replaces
bromine from a solution containing bromide ions.
Cl2(g) + 2Br-(aq) → Br2(g) + 2Cl-(aq)
Chlorine oxidises the bromide ions by
removing an electron from it. Bromine gas
is then liberated from the solution and is
detected by its reddish-brown colour.
Chapter 22: Non-metals
There are several methods to collect gases from experiments
depending on the solubility and density of the gas.
Method
Suitable gases
Downward displacement of water For gases which are insoluble or slightly soluble in
water
(e.g. oxygen, hydrogen, nitrogen, carbon dioxide)
Downward displacement of air /
upward delivery
For gases which are less dense than air
(e.g. hydrogen, ammonia)
Upward displacement of air /
downward delivery
For gases which are denser than air
(e.g. chlorine, carbon dioxide, sulphur dioxide)
Using a gas syringe (for any gas)
For any gas
Chapter 22: Non-metals
Moderately active metals, such as zinc, are used to react with mineral
acids to produce hydrogen gas.
Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)
The liberated hydrogen gas
is then bubbled through a
solution of concentrated
sulphuric acid.
Concentrated sulphuric acid
acts as a drying agent as it
removes any water
molecules present in the gas.
Chapter 22: Non-metals
Chlorine can be prepared by
removing hydrogen from
hydrochloric acid using an
oxidising agent, e.g.,
manganese dioxide.
Concentrated hydrochloric
acid is added to manganese
dioxide and the mixture is
heated.
MnO2(s) + 4HCl(l) → MnCl2(aq) + 2H2O(l)
+ Cl2(g)
Since chlorine is denser than air, it is
collected using downward delivery.
Chapter 22: Non-metals
When hydrogen peroxide is added to manganese dioxide, it
decomposes at room temperature, liberating oxygen gas.
2H2O2(l) → 2H2O(l) + O2(g)
This method of collecting
oxygen is known as
downward displacement of
water.
Chapter 22: Non-metals
Carbon dioxide is normally produced by the action of dilute hydrochloric
acid on marble chips.
CaCO3(s) + 2HCl(aq) → CaCl2(aq) +H2O(l) + CO2(g)
The gas can be collected by the downward delivery method.
Chapter 22: Non-metals
Sulphur dioxide can be prepared by treating sodium sulphite with
dilute sulphuric acid or hydrochloric acid.
Na2SO3(s) + 2HCl(aq) → 2NaCl (aq) +H2O(l) + SO2(g)
The SO2 produced is passed
through a gas washing bottle
containing concentrated
sulphuric acid. The gas is
dried and collected by
downward delivery.
Chapter 22: Non-metals
Ammonia can be prepared by heating an ammonium salt with a strong
base. In the lab, ammonia is prepared by heating a mixture of solid
ammonium chloride and calcium hydroxide.
2NH4Cl(s) + Ca(OH)2(aq) → CaCl2(s) +2H2O(l) + 2NH3(g)
Ammonia gas is
collected by upward
delivery as it is less
dense than air. Since
water is also
produced, the gas is
dried by passing
through a drying
tower filled with a
drying agent.
Chapter 22: Non-metals
Steam is mixed with methane (the main constituent of natural gas),
with a nickel catalyst at a temperature of 1200 °C and 50 atm
pressure to produce hydrogen gas.
CH4(g) + H2O(g) → CO(g) + 3H2(g)
Chapter 22: Non-metals
The mercury cell process
•
•
•
•
•
•
•
Chlorine is produced by the electrolysis of a concentrated aqueous
solution of sodium chloride known as brine.
The anode is made of graphite (or titanium) while the cathode is made
of mercury.
Chloride ions migrate to the anode and are discharged.
Sodium ions are preferentially discharged to form sodium.
Sodium combines with the mercury cathode to form sodium amalgam.
The amalgam is treated with water to produce sodium hydroxide and
hydrogen gas. The mercury is thus freed up for use as cathode again.
Since chlorine reacts with sodium hydroxide, they must be produced
in separate chambers and kept apart. This is achieved by the use of a
circulating mercury cathode.
At the anode: 2Cl- (aq) – 2e-
Cl2 (g)
Chlorine formed
At the cathode: Na+ (aq) + e-
Na (l)
Chapter 22: Non-metals
The membrane cell process
• The anode and cathode are separated by an ionexchange membrane.
• The membrane allows sodium ions and water to
pass through, but not chloride ions.
At the anode: 2Cl- (aq) – 2e-
Cl2 (g)
Chlorine formed
At the cathode: 2H+ (aq) + 2e-
H2 (g)
Chapter 22: Non-metals
The Contact Process
• Most of the sulphuric acid in the world today is
manufactured by the Contact Process.
• The Contact Process involves the catalytic
oxidation of sulphur dioxide, SO2, to sulphur
trioxide, SO3.
Chapter 22: Non-metals
Sulphur dioxide
+
Excess Air
Sulphur dioxide
(from burning of sulphur or
roasting of iron sulphide)
450 oC
1 – 2 atm
Vanadium(V) oxide
catalyst
unreacted
sulphur dioxide
Sulphur trioxide
dissolved in conc. sulphuric
acid
Sulphuric acid
Water
Oleum
Chapter 22: Non-metals
Step 1:
Conversion of Sulphur to Sulphur Dioxide
Sulphur dioxide is obtained from the burning of sulphur.
Most of the sulphur is obtained as a by-product of petroleum
refining. Sulphur burns in air to form a colourless pungent
gas called sulphur dioxide:
S(s) + O2(g)  SO2(g)
In some factories, sulphur dioxide is obtained as a byproduct from the roasting of iron pyrites in the extraction of
iron.
4FeS2(s) + 11O2  2Fe2O3(s) + 8SO2(g)
Chapter 22: Non-metals
Step2: Conversion of Sulphur Dioxide to Sulphur Trioxide
The sulphur dioxide is mixed with excess air and passed through a
filter to remove impurities and particles before entering the reaction
chamber.
The reaction chamber (converter) contains finely divided vanadium(V)
oxide as a catalyst at a temperature of about 450 °C – 500 °C. The
conversion of sulphur dioxide to sulphur trioxide occurs.
2SO2(g) + O2(g)
2SO3(g) ∆H = -189 kJmol-1
The heat evolved in the exothermic reaction maintains the
temperature of the catalyst. By using several converters in series and a
slight excess of oxygen, about 98% conversion of sulphur dioxide into
sulphur trioxide is achieved.
Chapter 22: Non-metals
Step 3:
Conversion of Sulphur Trioxide into Oleum
The sulphur trioxide is dissolved in concentrated sulphuric acid to form
a fuming liquid called oleum:
SO3(g) + H2SO4(l)  H2S2O7(l)
Sulphur trioxide is not dissolved directly in water because the reaction is
extremely vigorous and will result in the production of a mist of fine
sulphuric acid particles which is damaging to health.
Step 4:
Conversion of Oleum to Sulphuric Acid
The oleum obtained is carefully diluted with the correct amount of water
to form concentrated sulphuric acid:
H2S2O7(l) + H2O(l)  2H2SO4(l)
Chapter 22: Non-metals
Optimal Conditions for the Conversion
of Sulphur Dioxide to Sulphur Trioxide
The oxidation of sulphur dioxide to sulphur trioxide is a
reversible reaction, and is therefore affected by the
experimental conditions.
2SO2(g) + O2(g)
2SO3(g)
∆H = -189 kJmol-1
- As it is an exothermic reaction, lower temperatures would
favour the production of more sulphur trioxide and result in a
higher yield. A temperature of 450 °C is favourable.
- Higher pressure would favour the yield of the product.
However, extreme high pressure is not necessary as the yield is
already very high (98%) at a pressure of 1 – 2 atm.
- A vanadium catalyst, vanadium(V) oxide, is also used in this
reaction to speed up the rate of the reaction.
Chapter 22: Non-metals
The Haber Process
• The process for manufacturing ammonia from
nitrogen is called the Haber Process, named
after its inventor, Fritz Haber.
450 – 500 oC
The Haber Process
Chapter 22: Non-metals
•
Hydrogen is obtained by the action of steam on natural
gas or from the cracking of petroleum fractions.
•
A mixture of three parts by volume of hydrogen to one
part of nitrogen is compressed to a pressure of about
200 atm and passed over an iron catalyst heated to a
temperature of about 450 oC.
•
A yield of 17% – 20 % of ammonia is formed because the
reaction is reversible.
•
Under these conditions, the nitrogen reacts with the
hydrogen to form ammonia according to the equation:
2N2(g) + 3H2(g)
2NH3(g)
∆H = -92.4 kJ mol-1
Chapter 22: Non-metals
World’s Production of Ammonia
•
•
•
•
The annual production of ammonia has been increasing rapidly
since the end of World War II (Fig 24.6).
140 million tonnes of ammonia are produced per year.
Most of the ammonia is used in the manufacturing of fertilisers.
The use of fertilisers has increased the yield of food crops
which in turn supports a continuing rise in world population.
Fig 22.5 World production of ammonia is rising rapidly
Chapter 22: Non-metals
Uses of Ammonia
•
The ammonia manufactured in the Haber process is
used in the industry for many purposes.
•
Large quantities of ammonia are used in the
manufacture of fertilisers like ammonium nitrate,
ammonium sulphate and urea.
•
Ammonia is also used in making nitric acid. This is
done by the catalytic oxidation of ammonia into
nitrogen oxide which is then made into nitric acid. Nitric
acid can be used for making explosives and textiles.
•
Ammonia solution is commonly used as a cleaning
agent for dry cleaning and making window cleaners.
Ammonium fertiliser
Nitric acid
Window cleaner
Chapter 22: Non-metals
Uses of Sulphur Dioxide
• The most important use is for making sulphuric acid.
• It is used for bleaching wool and silk as it is a mild
reducing agent and would not damage the material.
• It is used for bleaching wood pulp for paper-making.
• It is used as a preservative for wine and other foodstuff
such as jams, tomato sauces and dried fruits. Sulphur
dioxide kills bacteria in the food and helps to maintain
the appearance of the foodstuff.
ChapterChapter
22 22: Non-metals
Preparations and collectives of
Quick Check 2
Non-metals
1. Why are some gases prepared in the laboratory passed
through concentrated sulphuric acid?
2. Why is quick lime (calcium oxide) used to dry
ammonia instead of concentrated sulphuric acid?
Solution
Chapter 22: Non-metals
Solution to Quick Check 2
1. To remove water vapour from the gas
2. Because alkaline ammonia reacts with sulphuric acid
to form ammonium sulphate.
2NH3 + H2SO4 → (NH4)2SO4
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