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 Poor conductors of heat and electricity and heat electricity except graphite Non-lustrous and cannot be Lustrous (having a polished, except graphite and sheen or glow) and iodine which are lustrous non- can be polished metals Solids at room May be solids, liquids or gases at temperature, except room temperature mercury
Chapter 22: Non-metals Differences between metals and non-metals Metals Non-Metals Strong, tough and have Not strong and have low tensile high tensile strength, strength, except diamond and except mercury and zinc carbon fibre Hard and have high Generally soft and have low density, except sodium density, except diamond and potassium High melting and boiling Low melting and boiling points, 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 Graphite • Colourless, transparent and has a very • Black high refractive index • Soft • Hardest known natural substance • Good electrical conductor • Non-conductor of electricity • Very high melting point (3652 C) • Good thermal conductor • Very high boiling point (4200 C) • Very high melting point (3550 C) • Very high boiling point (4827 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-metalsSolution 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, Not strong and have low tensile strength, except except mercury and zinc diamond and carbon fibre Hard and have high density, except sodium Generally soft and have low density, except diamond and potassium 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 Triatomic Diatomic oxygen, nitrogen and sulphur have oxygen (O2) oxygen (O3) allotropes as well. 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 Have 4–8 electrons in the outermost shell shell Lose valence electron(s) to form Gain electron(s) to form anions cations or share valence electrons to form covalent molecules Electropositive Electronegative Lose electrons in the valence shell Gain electrons from other elements (oxidised) and make good reducing (reduced) and make good oxidising agents agents Cationic metals are discharged at the Anionic non-metals are discharged at cathode during electrolysis the anode during electrolysis
Chapter 22: Non-metals Metals Non-Metals Many metals displace hydrogen Do not react with dilute acids from dilute acids and do not displace hydrogen from dilute acids Form chlorides which are Form covalent chlorides which electrolytes but non-volatile are non-electrolytes but volatile Do not combine with hydrogen, React with hydrogen to form except the reactive elemental metals stable covalent hydrides which form metal hydrides Form basic oxides, except Cr2O3 Form acidic or neutral oxides (acidic), and Al, Zn, Pb (amphoteric)
Chapter 22: Non-metals Colourless, stable liquid Hydrogen: 2H2(g) + O2(g) → 2H2O(g) Carbon: C(s) + O2(g) → CO2(g) In the presence of Colourless, odourl insufficient oxygen, ess gas and an carbon monoxide is acidic oxide formed instead.
Chapter 22: Non-metals 2Cl2(g) + O2(g) → 2Cl2O(g) Anhydride of hypochlorous Chlorine 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 N2(g) + O2(g) → 2NO (g) Colourless gas and a toxic air Nitrogen pollutant. 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.
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 + Metals → Metal chlorides Chlorine 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 Electronegativity increases Oxidising power 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 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.
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 / For gases which are less dense than air upward delivery (e.g. hydrogen, ammonia) Upward displacement of air / For gases which are denser than air downward delivery (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 ion- exchange 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 Sulphur dioxide (from burning of sulphur or + roasting of iron sulphide) Excess Air 450 oC 1 – 2 atm Vanadium(V) oxide catalyst unreacted sulphur dioxide Sulphur trioxide dissolved in conc. sulphuric acid Water Oleum Sulphuric acid
Chapter 22: Non-metalsStep 1: Conversion of Sulphur to Sulphur DioxideSulphur dioxide is obtained from the burning of sulphur.Most of the sulphur is obtained as a by-product of petroleumrefining. Sulphur burns in air to form a colourless pungentgas 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 ofiron. 4FeS2(s) + 11O2 2Fe2O3(s) + 8SO2(g)
Chapter 22: Non-metalsStep2: Conversion of Sulphur Dioxide to Sulphur TrioxideThe sulphur dioxide is mixed with excess air and passed through afilter to remove impurities and particles before entering the reactionchamber.The reaction chamber (converter) contains finely divided vanadium(V)oxide as a catalyst at a temperature of about 450 C – 500 °C. Theconversion of sulphur dioxide to sulphur trioxide occurs. 2SO2(g) + O2(g) 2SO3(g) ∆H = -189 kJmol-1The heat evolved in the exothermic reaction maintains thetemperature of the catalyst. By using several converters in series and aslight excess of oxygen, about 98% conversion of sulphur dioxide intosulphur trioxide is achieved.
Chapter 22: Non-metalsStep 3: Conversion of Sulphur Trioxide into OleumThe sulphur trioxide is dissolved in concentrated sulphuric acid to forma fuming liquid called oleum: SO3(g) + H2SO4(l) H2S2O7(l)Sulphur trioxide is not dissolved directly in water because the reaction isextremely vigorous and will result in the production of a mist of finesulphuric 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 waterto form concentrated sulphuric acid: H2S2O7(l) + H2O(l) 2H2SO4(l)
Chapter 22: Non-metalsOptimal Conditions for the Conversionof 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.
Chapter 22 22: Non-metals ChapterPreparations and collectives ofNon-metals Check 2 Quick 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-metalsSolution to Quick Check 21. To remove water vapour from the gas2. Because alkaline ammonia reacts with sulphuric acid to form ammonium sulphate. 2NH3 + H2SO4 → (NH4)2SO4 Return