Chapter 1. Introduction Introduction 1.1 - Why Bromine?
Total Page：16
File Type：pdf, Size：1020Kb
CHAPTER 1 IntroductionIntroductionIntroduction Chapter 1. Introduction Introduction 1.1 - Why bromine? Why did we decide to deal with bromine and bromine compounds? What is so special about bromine compared to other elements? Why do we dedicate a whole textbook to it? The answers to these questions are to be found in this chapter. You are probably familiar with bromine from previous studies. - What are the properties of bromine? - What reactions of bromine do you know? Introduction 2 He 6 7 8 9 10 C N O F Ne 14 15 16 17 18 Si P S Cl Ar 33 34 35 36 Introduction As Se Br Kr 52 53 54 Te I Xn 84 85 86 Po At Rn Antoine Jerome Balard - the discoverer of bromine 9 IntroductionIntroductionIntroduction IntroductionIntroductionIntroduction Introduction Bromine belongs to the family of halogens. The meaning of the name, stemming from the Greek, is salt forming. The halogens are not found as naturally occurring free elements, but rather as different compounds, mostly with metals. Explain why? The properties of the different halogens show marked differences as well as Introduction considerable similarities, due to the identical arrangement of seven valence Introduction electrons. The place of bromine in this special group of elements, between chlorine and iodine, results in an absence of extreme properties. Bromine is less electronegative than fl uorine or chlorine, but its electronegativity is not as low as that of iodine and astatine. Nevertheless, bromine is suffi ciently electronegative to act as a distinctive non-metal element. Introduction 35 Introduction Br 79.8 electron affi nity ionization enegy electronegativity 11.81 eV -3.36 eV 2.8 Introduction Arrange the halogens according to their oxidation potential. Halogens are known for their ability to form many inorganic and organic compounds, ionic compounds, molecular compounds and even polymers. Similarly, halogen compounds possess many different properties and therefore have many application areas. Make a list of the bromine compounds you know from your studies and arrange them according to different bonds: - ionic compounds - molecular compounds 10 11 IntroductionIntroductionIntroduction IntroductionIntroductionIntroduction Introduction 1.2 - Bromine and its properties The discovery of bromine Bromine (Br2) was first isolated and discovered in 1825, by the 23-year-old French chemist Antoine J. Balard, who passed chlorine (Cl2) gas through a concentrated solution of seawater and observed an unexpected formation of a red colored substance. After separation of the material Balard found that the new substance was a volatile liquid with a pungent smell and a reddish-brown color. Balard Introduction identified the material as an element and the French Academy coined the name Introduction bromos, which in Greek means, “foul smelling”. At the beginning of the 19th century enough knowledge had accumulated to distinguish between certain groups of elements that were found to have similar chemical reactions. Following its discovery, bromine joined chlorine discovered in 1774 and iodine in 1811. The level of contemporary chemical laboratories was high enough to perform many different experiments. The rapid and surprising progress in bromine research was made possible Introduction because of the great similarity between bromine on the one hand and chlorine Introduction and iodine, which were already well-known to the investigators, on the other hand. Immediately after the discovery of bromine, Balard and many others started to investigate its properties. They prepared bromine compounds with sulfur, phosphorus, chlorine, iodine and hydrogen as well as metal bromides and bromates1, and described their properties. Likewise, the investigators succeeded in carrying out reactions of bromine with organic compounds, such as acetic acid and ethanol. An example Introduction of how some of these processes were formulated may be seen in the following paragraph. A very interesting document2 is the letter that Dolon sent to Bercellius in July 1826 in which he wrote: 1 Such as KBrO3 and NaBrO3 2 From the book: Discovery of the Elements, published by the Journal of Chemical Education, 1968 10 11 IntroductionIntroductionIntroduction IntroductionIntroductionIntroduction Introduction “And now the news…it is simply a new “body” that will find its place between chlorine and iodine. This discovery belongs to Balard from Montpellier. This new “body” is found in seawater. Balard extracted it from the mother liquid of Montpellier brine by treatment with chlorine, followed by distillation. He obtained a dark red liquid that boils at 47ºC. The vapors resemble those of nitric acid. The specific density is 3.The material is kept under sulfuric acid. It reacts with metals that are partly volatile, for example potassium compounds.” Introduction Introduction Read the letter and explain why there are differences between the boiling point and the density of the new “body” that Balard found and between the properties of the bromine appearing on the next page. - Why did Balard keep the bromine under sulfuric acid? - How does bromine react with potassium? Give the equation. Introduction - According to Dolon, the compound of bromine with potassium is volatile. Is Introduction that true? What could be the reason for this statement? - What are the vapors that resemble those of nitric acid? Introduction 12 13 IntroductionIntroductionIntroduction IntroductionIntroductionIntroduction Introduction P r o p e r t i e s Name of material: Bromine, Br2 Element, Bi-atomic molecules Color: reddish-brown Smell: Pungent Melting point: -7.25°C Boiling point: 59.5°C Introduction Density: 3.12 gram/cm3 (20°C) Introduction Solubility in water: Low (with reaction) 3.58 gram in 100 cm3 water (at 20°C). 3.52 gram in 100 cm3 water (at 50°C). Solubility in other solvents: Very soluble in alkanes, alcohols, ethers and carbon disulfide. Flammability: Inflammable Toxicity: Toxic material, destroys body tissues and causes burns also at low concentrations (ppm3), causes irritation of the nose, throat, skin and eyes. Typical reactions: Introduction - Reacts with many metals, especially when containing water Introduction - Reacts with many alkali metals - Causes addition and substitution reactions with many carbon compounds. Enthalpy change of melting (ΔH°m): 10.57 kJ/Mol Enthalpy change of boiling (ΔH°b): 30.0 kJ/Mol Bonding enthalpy: 193 kJ/Mol Answer the following questions based on the properties of bromine above. Introduction - In what physical phase does bromine exist at room temperature? - Explain the solubility data of bromine: a) in water b) in alkanes c) in alcohols d) in ethers e) in carbon disulfide 3 ppm - parts per million 12 13 IntroductionIntroductionIntroduction IntroductionIntroductionIntroduction Introduction - Why is breathing bromine dangerous and why is it a cause of burns of the skin and eyes? - How should a bromine leakage be handled (or how should bromine be neutralized)? State the advantages and disadvantages of each method you suggest. - Bromine is a highly corrosive material, especially when it is wet. What is the Introduction reason for this? What are the consequences? Introduction Corrosion: Deterioration process of solid material (usually metallic) as a result of contact with other material(s). Deterioration is usually accompanied by formation of holes, cracks or disintegration of the material. The process causes a change in the mechanical properties of the material, which may no longer suit its purpose. Introduction Chemical reactions of bromine Introduction As already mentioned, immediately after its discovery, studies of the properties of bromine started with the preparation of many different bromine compounds, and the collection of the information needed to characterize its properties. Bromine undergoes oxidation-reduction reactions with a wide range of materials, sometimes reacting as an oxidant and sometimes as a reductant. Bromine participates in certain auto-oxidation-reduction reactions. In other words, some of the bromine atoms act as oxidizing agents (their oxidation state decreases), and some act as reducing agents (their oxidation state increases). Some of the more Introduction important reactions of bromine are described in the following pages. Reaction with hydrogen: 1. H2(g) + Br2(g) 2HBr(g) Reaction with different metals, such as: 2. 2K(s) + Br2(l) → 2KBr(s) 3. 2Al(s) + 3Br2(l) → 2AlBr3(s) Reactions with different non-metals, such as: 4. Br2(l) + Cl2(g) 2BrCl(l) 14 15 IntroductionIntroductionIntroduction IntroductionIntroductionIntroduction Introduction + _ _ 2(l) 4(s) 2 (l) 3 (aq) (aq) 2 3(aq) 5. 3Br + 1⁄2P + 14H O → 8H O +6Br_ +2H PO_ 1 + 6. 3Br2(l)+ /8S8(s)+11H2O(l) → 7H3O (aq) +6Br (aq) +HSO4(aq) Reaction with ammonia: 7. 3Br2(l)+8NH3(g) → 6NH4Br(s)+N2(g) Reaction with water: + _ 2(l) 2 (l) 3 (aq) (aq) (aq) 8. Br +2H O H O +Br +HOBr Introduction Introduction The reaction of bromine in an aqueous solution is pH-dependent and accordingly different products may be formed; In very alkaline solutions_ (pH>13),_ the_ following reaction occurs: 9. Br2(l)+2OH(aq) → Br(aq)+OBr(aq)+H2O(l) In a less alkaline solution_ (pH<13),_ the following_ reaction occurs: 10. 3Br2(l)+6OH(aq) → 5Br(aq) +BrO3(aq) +3H2O(l) Bromine reacts with many organic compounds, of which we shall mention Introduction only a few. You can apply your knowledge and add reactions with other Introduction substances. Reaction with acetic acid: 11. CH3COOH(l)+Br2(l) → CH2BrCOOH(l) + HBr(g) Reaction with methane: light or heat 12. CH4(g) + Br2(g) → CH3Br(g) +HBr(g) 3 (g) 2(g) 2 2(g) (g) Introduction CH Br + Br → CH Br +HBr Reaction with ethene: 13. C2H4(g)+Br2(g) → C2H4Br2(g) Reaction with secondary alcohol, e.g., 2-propanol: 14. CH3CHOHCH3(l) + Br2(l) → CH3COCH3(l) +2HBr(g) Reaction with ketone, e.g., acetone: 15. CH3 COCH3(l) + Br2(l) → CH3COH2Br+HBr(g) 14 15 IntroductionIntroductionIntroduction IntroductionIntroductionIntroduction Introduction Arrange the above reactions into those in which bromine acts as oxidant, as reductant or as both at the same time. In the reaction between bromine and water HOBr(aq) is formed.