10 The Chemistry of Characteristic non-metals and their compounds.

Transcription

1 Chemistry Form 4 Page The Chemistry of Characteristic non-metals and their compounds NITROGEN See Chemistry for You - Haber process - pg , 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 (NO 2 ). 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 available commercially or through in-house air liquefaction plants. However the decomposition of sodium azide is one route to N 2 and decomposition is ammonium dichromate is another. Both reactions must only be carried out under controlled conditions by a professional. NaN 3 (300 C) 2Na + 3N 2 (NH 4 ) 2 Cr 2 O 7 N 2 + Cr 2 O 3 + 4H 2 O 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.

2 Chemistry Form 4 Page 57 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 NH 3 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.

3 Chemistry Form 4 Page 58 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 NH 3 - Ammonia Molecule NH 4 - Ammonium Ion 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. N 2 + 3H 2 2NH 3 + 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 discovered that if pressure, temperature and catalysts are properly regulated, the inactive nitrogen will react with hydrogen to form ammonia.

4 Chemistry Form 4 Page 59 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. ) The fountain experiment demonstrates the violence with which ammonia is absorbed by water. The ammonia absorption by water reduces the pressure in the flask, so that water escapes from the upper, narrow opening of the tube. Thus, the increased surface of the water leads to an increase in the speed of absorption till the water shoots into the glass flask like a fountain. During the process the colour of the indicator changes due to the alkaline effect of ammonia 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.

5 Chemistry Form 4 Page 60 - Chemical properties of NH 3 : combustion in oxygen Ammonia burns in air slightly enriched with oxygen to produce nitrogen and water. catalytic oxidation (to give NO and H2O); 4 NH 3 (g) + 3 O 2 (g) 2 N 2 (g) + 6 H 2 O (l) In the presence of a catalyst, ammonia reacts with oxygen to form nitrogen monoxide and water. (Platinum/Rhodium catalyst) 4 NH 3 (g) + 5 O 2 (g) 4 NO (g) + 6 H 2 O (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 NH 3 (g) 3 Cu (s) + N 2 (g) + 3H 2 O (l) alkalinity Is alkaline in water: NH 3 (g) + H 2 O (l) NH 4 OH (aq) neutralisation of acids - reacts with acids to form ammonium salts. NH 3 (g) + HNO 3 (aq) NH 4 NO 3 (aq) (Ammonium nitrate is an important fertilizer) FERTILIZERS e.g. NH 4 NO 3, (NH 4 ) 2 SO 4 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 ph b) 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: NH 4 Cl (s) NH 3 (g) + HCl (g) (NH4) 2 CO 3 (s) 2 NH 3 (g) + CO 2 (g) + H 2 O (l)

6 Chemistry Form 4 Page 61 Oxides of nitrogen, NO and NO 2 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 900 o C 4 NH 3 (g) + 5 O 2 (g) 4 NO (g) + 6 H 2 O (l) b) Nitrogen monoxide is cooled then oxidized to nitrogen dioxide by mixing with air. 4 NO (g) + 2 O 2 (g) 4 NO 2 (g) c) Nitrogen dioxide is reacted with water and oxygen to produce nitric acid. 4 NO 2 (g) + O 2 (g) + 2 H 2 O (l) 4 HNO 3 (aq) Revision of the formation of oxides of nitrogen in the internal combustion engine and their removal by a catalytic converter. (see Chemistry for You pg. ) NO 2 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 decomposes to lead (II) oxide, nitrogen dioxide and oxygen. 2 Pb(NO 3 ) 2 (s) 2 PbO (s) + 4 NO 2 (g) + O 2 (g)

7 Chemistry Form 4 Page 62 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 NO 2 (g) + 4 H 2 O (l) HNO 3 (aq) + HNO 2 (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 NO 2 (g) 4 MgO (s) + N 2 (g) Thermal dissociation of N2O4: nitrogen dioxide. Dinitrogen tetroxide Light yellow When dinitrogen tetroxide is heated, it decomposes into Nitrogen dioxide Dark brown N 2 O 4 (g) Decrease pressure Increase pressure 2 NO 2 (g) 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.

8 Chemistry Form 4 Page 63 Nitric acid as a dilute acid o It is an unusual acid. o When dilute it acts like an acid. It is a strong acid (i.e. fully dissociated into its ions) HNO 3 (l) H + (aq) + NO 3 - (aq) It reacts with bases and carbonates as all acids do. Metal carbonate + acid Salt + Water + Carbon dioxide Na 2 CO 3 (s) + 2 HNO 3 (aq) 2 NaNO 3 (aq) + H 2 O (l) + CO 2 (g) Base + acid Salt + Water NaOH (aq) + HNO 3 (aq) NaNO 3 (aq) + H 2 O (l) But when the dilute acid is reacted with metals, it always acts as an oxidising agent thus complicating what happens. The hydrogen initially produced is oxidized to water and the reduction products of nitric acid are also produced: nitrogen dioxide, nitrogen oxide, ammonia. Oxidising action of the concentrated acid a) with metals (exemplified by its reaction with copper) When concentrated nitric acid is added to copper, copper is oxidized to copper (II) ions. Loss of electrons = oxidation Cu (s) + 4 HNO 3 (l) Cu(NO 3 ) 2 (aq) + 2 NO 2 (g) + 2H 2 O (l) o At the same time, the concentrated nitric acid is reduced to nitrogen dioxide. o So when concentrated nitric acid is added onto copper, nitrogen dioxide (a brown gas) is given off and the solution turns blue due to the formation of copper (II) ions. b) with an iron (ll) salt. o It also oxidizes an iron (II) salt to an iron (III) salt. o Concentrated nitric acid is added onto iron (II) sulphate solution. o The solution is heated o The iron (II) sulphate (pale green) changes to iron (III) (yellow/brown) and nitrogen dioxide (brown gas) is given off. 1 1 Note when conc. Nitric acid acts as an oxidising agent, it is reduced to nitrogen dioxide.

9 Chemistry Form 4 Page 64 Metallic Nitrates o General methods of preparation HNO 3 (aq) nitric acid reacts with metals to form the metallic nitrates e.g. Cu(NO 3 ) 2 see pg. 63 o solubility all nitrates are soluble o action of heat on nitrates see notes pg. 48 o test for NO3 see notes pg 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 S 8 3 allotropes: monoclinic, rhombic, plastic a) Rhombic sulphur Is stable below 96 o C. The crystals of rhombic sulphur are diamond shaped. b) Monoclinic sulphur this is stable above 96 o C. 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 shown above. When it is heated slowly above 95.5 ºC, it is converted to monoclinic sulphur. Both of these forms are insoluble in water but soluble in carbon disulfide, CS 2. When sulphur is heated above 113 ºC, it melts to form a pale yellow liquid, which becomes darker and more viscous as the temperature is increased. If liquid sulphur is heated to its boiling 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.

10 Chemistry Form 4 Page 65 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, and o 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 heat used 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 Frasch Process, 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, KNO 3, 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) + O 2 (g) SO 2 (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

11 Chemistry Form 4 Page 66 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 SO 2 The laboratory preparation of dry sulphur dioxide by the reaction of a) a dilute acid on a sulfite Sodium sulfite (Na 2 SO 3 ) and dilute hydrochloric acid (HCl) Na 2 SO 3 (s) + 2 HCl (aq) 2 NaCl (aq) + SO 2 (g) + H 2 O (l) 1. The two are heated in a flask. 2. Sulphur dioxide (SO 2 ) 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 Na 2 SO 3 b) concentrated sulphuric acid on copper. Copper and concentrated sulphuric acid are mixed together and then heated. Sulphur dioxide is given off: Cu (s) + 2 H 2 SO 4 (l) CuSO 4 (s) + 2H 2 O (l) + SO 2 (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 concentrated sulphuric acid acts as an oxidising agent. So it reacts with copper and concentrated sulphuric acid is reduced to sulphur dioxide.

12 Chemistry Form 4 Page 67 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). H 2 O (l) + SO 2 (g) H 2 SO 3 (aq) 2 H + (aq) + SO -- 3 (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 colourless 2. 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 dioxide gas. 5. Some coloured things lose colour when reduced as SO 2 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. SO 3 - 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 increasing concentration of these molecules in the atmosphere in recent years has caused the environmental problem we know as acid rain. Complete: SO 3 (g) + H 2 O (l) H 2 SO 4 (aq) sulphuric acid Sulphur dioxide normally acts a/n agent. But it behaves as such when the presence 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.

13 Chemistry Form 4 Page 68 Sulphuric Acid - H 2 SO 4 The manufacture of sulphuric acid by the Contact process The Contact Process: makes sulphur dioxide SO 2 ; converts the sulphur dioxide into sulphur trioxide SO 3 (the reversible reaction at the heart of the process); converts the sulphur trioxide into concentrated sulphuric acid H 2 SO 4 Process divided into 3 stages: 1. Preparation and purification of SO 2 2. Catalytic oxidation (using Vanadium oxide catalyst) of SO 2 to SO 3 3. Conversion of SO 2 to H 2 SO 4 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 - the reaction is so uncontrollable that it creates a fog of sulphuric acid. Instead, the sulphur trioxide is first dissolved in concentrated sulphuric acid: The product is known as fuming sulphuric acid or oleum. This can then be reacted safely with water to produce concentrated sulphuric acid.

14 Chemistry Form 4 Page 69 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 + Hydrogen Zn (s) + H 2 SO 4 (aq) Na 2 SO 4 (aq) + H 2 (g) It reacts with metal carbonates: Metal Carbonate + Acid Salt + Carbon dioxide + water Na 2 CO 3 (s) + H 2 SO 4 (aq) Na 2 SO 4 (aq) + CO 2 (g) + H 2 O (l) It reacts with bases Base + Acid Salt + Water NaOH (aq) + H 2 SO 4 (aq) Na 2 SO 4 (aq) + H 2 O (l) b) When concentrated: Concentrated sulphuric acid is not acidic. This happens as an acid becomes acidic when it is dissolved 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 acid is 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. CuSO 4.5H 2 O s) CuSO 4 (s) + 5 H 2 O (l) taken by the acid It also removes the elements hydrogen and oxygen (2:1) from compounds like sugar. C 12 H 22 O 11 (s) 12 C (s) + 11 H 2 O (l) taken by the acid

15 Chemistry Form 4 Page 70 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 warmed with concentrated Sulphuric Acid, H 2 SO 4. reaction of sulphuric acid with potassium nitrate can be used to produce nitric acid 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) + H 2 SO 3 (aq) NaHSO 3 (aq) + H 2 O (l) b) Normal salt: NaHSO 3 (aq) + NaOH (aq) Na 2 SO 3 (aq) + H 2 O (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, CaSO4.2H 2 O 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 SO 3 2- and SO covered in Unit 9, Topic 9.2

16 Chemistry Form 4 Page 71 Chlorine 10.3 Halogens 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 KMnO 4 (s) + 16 HCl (aq) 2 KCl (aq) + 2 MnCl 2 (aq) + 8 H 2 O (l) + 5 Cl 2 (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 Test for chlorine. a) Electrolysis of molten sodium chloride b) Electrolysis of sodium chloride solution (brine) It bleaches damp litmus paper Physical properties. Greenish-yellow gas with a choking smell Denser than air Poisonous

17 Chemistry Form 4 Page 72 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 Cl 2 (g) + H 2 S (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 Cl 2 (g) 2 FeCl 3 (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) + Cl 2 (g) CuCl 2 (g) Zn (s) + Cl 2 (g) ZnCl 2 (g) o HYDROGEN gas jars placed mouth to mouth. Reaction explosive in sunlight H 2 (g) + Cl 2 (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 FeCl 2 (aq) + Cl 2 (g) 2 FeCl 3 (aq) It also oxidizes sulphite ion to the sulphate ion. Displacement reactions of one halogen by another. It displaces iodine from potassium iodide solution. Cl 2 (g) + 2 KI (aq) 2 KCl (aq) + I 2 (aq)

18 Chemistry Form 4 Page 73 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, CHCl 3 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; Hydrogen chloride Concentrated sulphuric acid is added onto sodium chloride NaCl (s) + H 2 SO 4 (aq) NaHSO 4 (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)

19 Chemistry Form 4 Page 74 MOST COMMON TEST o Produces dense white fumes in the presence of ammonia as ammonium chloride forms. Properties. HCl (g) + NH 3 (g) NH 4 Cl (aq) 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 HCl 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 of the 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. water Reactions of dilute hydrochloric acid as a typical acid. Metal + Acid Salt + Hydrogen Zn (s) + 2 HCl (aq) ZnCl 2 (aq) + H 2 (g) Metal Carbonate + Acid Salt + Carbon dioxide + Water Na 2 CO 3 (s) + 2 HCl (aq) 2 NaCl (aq) + CO 2 (g) + H 2 O (l) Alkali + Acid Salt + Water NaOH (aq) + HCl (aq) NaCl (aq) + H 2 O (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) + H 2 SO 4 (aq) Na 2 SO 4 (s) + 2 HCl (g) ii) Direct combination of hydrogen with chlorine. The hydrogen chloride is then dissolved in water to form hydrochloric acid.

20 Chemistry Form 4 Page 75 H 2 (g) + Cl 2 (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 General methods of preparing metallic chlorides. All attacked by chlorine to form a chloride The equation that takes place is: 2 Fe (s) + 3Cl 2 (g) 2FeCl 3 (s) To make Iron (II) chloride, iron is reacted with HCl (g) or (aq): Fe (s) + 2HCl (g) FeCl 2 (aq) + H 2 (g) Anhydrous calcium chloride is a deliquescent substance as it absorbs water vapour from the atmosphere and dissolves in it. 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

21 Chemistry Form 4 Page 76 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 copper metal. One of the products is sulphur dioxide gas (i) Give an equation for the reaction and use it to explain why concentrated sulphuric 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 is not required). (2 marks) (c) Concentrated sulphuric acid acts as a dehydrating agent in its reaction with sucrose, C 12 H 22 O 11. 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)