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Bromine
Introduction
Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I), and Astatine (At) are the five elements that make up the halogen group of the periodic table. In Greek, 'halos' means sea salts, ‘genes’ means born. Except for astatine, which is radioactive and only exists in trace amounts, these elements react with metals to produce salts and are plentiful in nature. Because the elements' valence shells have seven electrons, the typical electronic configuration of Br is $\mathrm{[Ar]\:4s^2 \:4p^4}$.
Occurrence and Extraction of Bromine
Bromine is the 47th most prevalent element in the earth's crust, with a concentration of 2.5 ppm by weight. It's mostly found as bromides in seawater, mineral springs, and deposits. It was discovered in 1826 by A J Balardin, who used chlorine to purify the mother liquid left behind after the crystallisation of NaCl from sea water. Due to its unpleasant odour, he dubbed the liquid as bromine (Greek bromos, stink).
$$\mathrm{Cl_2 + 2Br^−\:\rightarrow\:2Cl^− + Br_2}$$
A stream of air removes the released bromine, which is then passed through a solution of $\mathrm{Na_2CO_3}$ to produce a mixture of $\mathrm{NaBr}$ and $\mathrm{NaBrO_3}$.
$$\mathrm{3Br_2 + 3Na_2CO_3\:\rightarrow\:5NaBr + NaBrO_3 + 3CO_2}$$
To obtain pure bromine, the solution is acidified and distilled.
$$\mathrm{5NaBr + NaBrO_3 + 3H_2SO_4\:\rightarrow\:3Na_2SO_4 + 5HBr + HBrO_3}$$
$$\mathrm{5HBr + HBrO_3 \:\rightarrow\:3Br_2 + 3H_2O}$$
Physical Properties of Bromine
The physical properties of Bromine and the other halogen congeners can be compared using the table below:
Property | F | Cl | Br | I |
---|---|---|---|---|
Colour (in liquid) | Clear Yellow | Amber Yellow | Reddish Brown | Dark Solid |
Colour (in vapour) | Pale Yellow | Greenish Yellow | Orange Red | Violet |
Enthalpy of Fusion (kJ/mol) | 0.51 | 6.41 | 10.57 | 15.52 |
Enthalpy of Vapourization (kJ/mol) | 6.54 | 20.41 | 29.56 | 41.95 |
Standard Electrode Potential (V) | + 2.87 | + 1.36 | + 1.06 | + 0.53 |
Bond Energy (kJ/mol) | 158.8 | 242.6 | 192.8 | 151.1 |
Density $\mathrm{(g/cm^{-3})}$ | 1.513 | 1.655 | 3.187 | 3.960 |
Boiling Point (K) | 85 | 239 | 333 | 458 |
Melting Point (K) | 54 | 172 | 266 | 387 |
Electronegativity | 4.0 | 3.0 | 2.8 | 2.5 |
Electron Affinity (kJ/mol) | 333 | 349 | 325 | 296 |
Ionisation Energy (kJ/mol) | 1681 | 1256 | 1143 | 1009 |
Ionic Size (pm) | 133 | 184 | 196 | 220 |
Atomic Size (pm) | 72 | 99 | 114 | 133 |
Chemical Properties of Bromine
Bromine is less reactive than chlorine but more active than iodine, and it reacts with a wide range of metals, non-metals, and compounds. For oxidising, bleaching, and disinfection, bromine aqueous solutions are utilised. The following are some instances of its oxidising properties:
$$\mathrm{Na_2S_2O_3 + Br_2 + H_2O\:\rightarrow\:Na_2SO_4 + S + 2HBr}$$
$$\mathrm{Na_3AsO_3 + Br_2 + H_2O\:\rightarrow\:Na_3AsO_4 + 2HBr}$$
Bromine forms hypo brominates when it interacts with a cold NaOH solution. Bromates are formed when hot solutions are used.
$$\mathrm{Br_2 + 2NaOH (cold)\:\rightarrow\:NaBr + NaOBr + H_2O}$$
$$\mathrm{3Br_2 + 6NaOH (hot)\:\rightarrow\: 5NaBr + NaBrO_3 + 3H_2O}$$
Compounds of Bromine
Hydrogen Bromide: It is made by passing a hydrogen and bromine combination through an electrically heated platinum spiral. Conc. $\mathrm{H_2SO_4}$ treatment of metal bromides does not yield HBr because the resultant HBr is oxidised to $\mathrm{Br_2}$ by conc. $\mathrm{H_2SO_4}$
Oxides of Bromine: Many of the oxides formed by Bromine decompose even below room temperature. Some important oxides of Bromine are:
Bromine Monoxide $\mathrm{(Br_2O)}$: Bromine vapours react with dry HgO at 323–343 K to produce it.
Bromine Dioxide $\mathrm{(BrO_2)}$: Bromine is ozonolyzed at a low temperature to make Bromine Dioxide
Bromine Trioxide $\mathrm{(BrO_3)}$: It is made via ozonolysis of bromine at temperatures ranging from –5 to 10 degrees Celsius.
Oxyacids of Bromine: Hypobromous acid (HOBr) and bromic acid $\mathrm{(HBrO_3)}$ are two oxyacids formed by bromine. Bromites, on the other hand, are bromous acid salts $\mathrm{(HBrO_2)}$. Bromine water is treated with newly precipitated mercuric oxide or silver oxide to produce hypobromous acid $\mathrm{(HOBr)}$.
Uses of Bromine
It is employed as an oxidizer as well as in the production of disinfectants and other key organic compounds like tetraethyl lead.
In photography, silver bromide is utilised.
As a laboratory reagent, HBr is employed.
Bromine oxides and oxyacids are utilised as oxidising agents.
Conclusion
Bromine bears an atomic number of 35 in the periodic table. It has a characteristic odour and is fairly abundant in the earth’s crust. The unique property of Bromine would be that it is only non-metal present in liquid state at room temperature and ambient pressure. Bromine has ample uses in daily life and in industries.
FAQs
Q1. What are some of the properties of Bromine?
Ans: It is a reddish brown liquid with a boiling point of 58.8°C and a freezing point of –7.3°C. It's very flammable and produces powerful fumes that irritate the throat and lungs. Bromine is less reactive than chlorine but more active than iodine, and it reacts with a wide variety of metals, nonmetals, and compounds.
Q2. How would you produce HBr in the laboratory?
Ans: $\mathrm{HBr}$ can be produced by the action of conc. $\mathrm{H_3PO_4}$ on metal bromides. The chemical reaction involved is
$$\mathrm{3NaBr + H_3PO_4 \:\xrightarrow{\Delta}\:Na_3PO_4 + 3HBr}$$
Q3. How does $\mathrm{BrO_2}$ react with alkalis?
Ans: It decomposes at 0°C and is a yellow solid only at –40°C. It forms a combination of bromides and bromates when it dissolves in alkalies.
$$\mathrm{6BrO_2 + 6NaOH\:\rightarrow\:5NaBrO_3 + NaBr + 3H_2O}$$
Q4. Write a brief explanation of Bromine Monoxide $\mathrm{(Br_2O)}$.
(i) Bromine vapours react with dry HgO at 323–343 K to produce Bromine Monoxide.
$$\mathrm{2HgO + 2Br_2\:\rightarrow\:HgO.HgBr_2 + Br_2O}$$
(ii) It's a dark brown liquid with a freezing point of –17.5 degrees Celsius. In the presence of alkalis, it disproportionates.
$$\mathrm{6NaOH + 6Br_2O\:\rightarrow\:5NaBrO_3 + NaBr + 3H_2O}$$
(iii) It is an anhydride of $\mathrm{HBrO}$ because it dissolves in water to form hypobromous acid. It operates as an oxidizing agent, oxidizing iodine to iodine pentoxide.
$$\mathrm{5Br_2O + I_2\:\rightarrow\:I_2O_5 + 5Br_2}$$
Q5. Why does dilute solution of $\mathrm{HBr}$ tends to turn yellow?
Ans: Because of the oxidation of $\mathrm{HBr}$ to $\mathrm{Br_2}$, dilute aqueous solutions of $\mathrm{HBr}$ are particularly reactive and become yellow.
- Related Articles
- What is Bromine?
- Difference Between Bromine and Chlorine
- What type of chemical bond is formed between:(a) Potassium and bromine? (b) Carbon and bromine?
- What is the property of Bromine?
- When a gas jar containing air is inverted over a gas jar containing bromine vapour, the red-brown bromine vapour diffuses into air. Explain how bromine vapour diffuse into air.
- When a gas jar full of air is placed upside down on a gas jar full of bromine vapours, the red-brown vapours of bromine from the lower jar go upward into the jar containing air. In this experiment :(a) air is heavier than bromine(b) both air and bromine have the same density(c) bromine is heavier than air(d) bromine cannot be heavier than air because it is going upwards against gravity
- Bromine and air take about 15 minutes to diffuse completely but bromine diffuses into a vacuum very rapidly. Why is this so?
- Bromine particles are almost twice as heavy as chlorine particles. Which gas will diffuse faster; bromine (vapour) or chlorine? Explain your answer.
- Explain why, ethene decolourises bromine water whereas ethane does not.
- If bromine atom is available in the form of say, two isotopes 7935Br (49.7%) and 8135Br (50.3%), calculate the average atomic mass of bromine atom.
- The elements which normally exist in the liquid state are :(a) bromine and iodine (b) mercury and chlorine(c) iodine and mercury (d) bromine and mercury
- State whether the following statement is true or false :Red-brown bromine vapour diffuse into air in a gas jar but the colourless air molecules do not diffuse into bromine vapour.
- Which of the two diffuses slower: bromine vapour into air or copper sulphate into water?
- Which of the following hydrocarbons can decolourise bromine water and which cannot? Why?C6H12, C6H14, C6H10
- When a gas jar containing colourless air is kept upside down over a gas jar full of brown-coloured bromine vapour, then after some time, the brown colour of bromine vapour spreads into the upper gas jar making both the gas jars appear brown in colour. Which of the following conclusion obtained from these observations is incorrect?(a) bromine vapour is made of tiny particles which are moving(b) air is made up of tiny particles which are moving(c) the particles of bromine are moving but those of air are not moving(d) even though bromine vapour is heavier that air, it can move up against gravity
