C22 non metals

Chapter 22: Non-metals


• Describe the physical and chemical properties of Describe the physical and chemical properties of non – metals. non – metals.

• Describe the industrial preparation of chlorine, Describe the industrial preparation of chlorine, sulphuric acid and ammonia.sulphuric acid and ammonia.

• List the uses of the non – metals: carbon, sulphur, List the uses of the non – metals: carbon, sulphur, phosphorus, chlorine, nitrogen, silicon and their phosphorus, chlorine, nitrogen, silicon and their compounds.compounds.

Learning OutcomesYou should be able to:


MetalsNon-metals

Semi-metal

Non-metals like Hydrogen (H), carbon (C), Nitrogen (N) are found on the right side of the Periodic Table.

C N

H


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 non-metals

Solids at room temperature, except mercury

May be solids, liquids or gases atroom temperature

Differences between metals and non-metals


Metals Non-MetalsStrong, 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 lowdensity, except diamond

High melting and boiling points

Low melting and boiling points,except diamond and graphite

Differences between metals and non-metals


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)

Hydrogen (H)


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)


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


• Low melting point (–218 °C) and low boiling point (–183 °C)


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.

Graphite• Black• Soft• Good electrical conductor• Very high melting point (3652 °C)• Very high boiling point (4200 °C)

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)


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


• Allotropes – rhombic and monoclinic sulphur

• Rhombic sulphur has a melting point of 113 °C and boiling point of 445 °C


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


• Low melting point (–210 °C)

• Low boiling point (–196 °C)


Quick Check 1List the differences between metals and non-metals.

Solution


Solution to Quick Check 1

Strong, tough and have high tensile strength, except mercury and zinc

Not strong and have low tensile strength, exceptdiamond 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 andgraphite

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 graphiteand Iodine which is lustrous non-metals

Solids at room temperature, except mercury May be solids, liquids or gases at room temperature

Return


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.

Monoclinic sulphurRhombic sulphur


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 anionsor share valence electrons to formcovalent 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 thecathode during electrolysis

Anionic non-metals are discharged atthe anode during electrolysis


Metals Non-Metals

Many metals displace hydrogenfrom dilute acids

Do not react with dilute acidsand do not displace hydrogenfrom dilute acids

Form chlorides which areelectrolytes but non-volatile

Form covalent chlorides whichare non-electrolytes but volatile

Do not combine with hydrogen,except the reactive elemental metalswhich form metal hydrides

React with hydrogen to formstable covalent hydrides

Form basic oxides, except Cr2O3

(acidic), and Al, Zn, Pb (amphoteric)

Form acidic or neutral oxides


Hydrogen: 2H2(g) + O2(g) → 2H2O(g)

Colourless, stable liquid

Carbon: C(s) + O2(g) → CO2(g)

Colourless, odourless gas and an acidic oxide

In the presence of insufficient oxygen, carbon monoxide is formed instead.


2Cl2(g) + O2(g) → 2Cl2O(g)

Chlorine

Cl2(g) + 2O2(g) → 2ClO2(g)

The chloride oxides are acidic and highly unstable, reacts with alkalis to form salt.

Anhydride of hypochlorous acid. It is an orange gas.

Reddish yellow gas, a useful oxidising agent.


Sulphur S(s) + O2(g) → SO2(g)

NitrogenN2(g) + O2(g) → 2NO (g)

2NO(g) + O2(g) → 2NO2(g)

Acidic oxide, colourless gas with a pungent smell that dissolves in water to form acid.

Colourless gas and a toxic air

pollutant.

Reddish brown toxic gas, which has a sharp biting odour and is an air pollutant.


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)

Sulphur

Nitrogen N2(g) + 3Ca(s) → Ca3N2(s)

S(S) + Zn(s) → ZnS(s)

Hydrogen + Alkali metals → Metal hydrides

Nitrogen + Reactive metals → Metal nitrides

Sulphur + Metals → Metal sulphides


Chlorine

Oxygen

3Cl2(g) + 2Al(s) → 2AlCl3(s)

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.

Chlorine + Metals → Metal chlorides

Oxygen + Metals → Metal oxides


MetalsNon-metals

Semi-metal

Oxidising power increasesEl

ectro

nega

tivity

incr

ease

s

Electronegativity increases

Oxi

disi

ng p

ower

incr

ease

s

Nitrogen, oxygen, bromine, chlorine and fluorine are all good oxidising agents with fluorine being the strongest.


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


A more reactive non-metal would be able to displace a less reactive non-metal 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.


There are several methods to collect gases from experiments depending on the solubility and density of the gas.

Method Suitable gasesDownward 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


Moderately active metals, such as zinc, are used to react with mineral acids to produce hydrogen gas.

The liberated hydrogen gas is then bubbled through a solution of concentrated sulphuric acid.

Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)

Concentrated sulphuric acid acts as a drying agent as it removes any water molecules present in the gas.


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.


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.


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.


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.


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.


CH4(g) + H2O(g) → CO(g) + 3H2(g)

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.


• 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.

The mercury cell process

At the anode: 2Cl- (aq) – 2e- Cl2 (g)

At the cathode: Na+ (aq) + e- Na (l)Chlorine formed


• The anode and cathode are separated by an ion-exchange membrane.

• The membrane allows sodium ions and water to pass through, but not chloride ions.

The membrane cell process

At the anode: 2Cl- (aq) – 2e- Cl2 (g)

At the cathode: 2H+ (aq) + 2e- H2 (g)Chlorine formed


• 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.

The Contact Process


Sulphur dioxide(from burning of sulphur or roasting of iron sulphide)

Sulphur dioxide+

Excess Air

450 oC 1 – 2 atm

Vanadium(V) oxide catalyst

Sulphur trioxide dissolved in conc. sulphuric

acid

Oleum Sulphuric acid Water

unreactedsulphur dioxide


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 by-product from the roasting of iron pyrites in the extraction of iron.

4FeS2(s) + 11O2 2Fe2O3(s) + 8SO2(g)


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.

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.

2SO2(g) + O2(g)


Step 3: Conversion of Sulphur Trioxide into OleumThe 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 AcidThe oleum obtained is carefully diluted with the correct amount of water to form concentrated sulphuric acid:

H2S2O7(l) + H2O(l) 2H2SO4(l)


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.


The Haber Process• The process for manufacturing ammonia from

nitrogen is called the Haber Process, named after its inventor, Fritz Haber.

The Haber Process

450 – 500 oC


• 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


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


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 themanufacture 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


• 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.

Uses of Sulphur Dioxide


Preparations and collectives of Non-metals

Chapter 22

Quick Check 2

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


Solution to Quick Check 21. To remove water vapour from the gas

2. Because alkaline ammonia reacts with sulphuric acid to form ammonium sulphate.

2NH3 + H2SO4 → (NH4)2SO4

Return

C22 non metals

Education

Transcript of C22 non metals