What Is Lithium Bromide? Composition, Properties, and Applications
Lithium bromide is an ionic compound of lithium and bromine. Lithium is an alkali metal that has 3 electrons. The electronic configuration of lithium is 2,1. Thus, it has 1 electron in its valence shell. On the other hand, bromine is a non – metal that has 35 electrons in its single atom. Its electronic configuration is 2,8,18,7. Thus, it has 7 electrons in its valence shell. Lithium can attain electronic configuration like nearest noble gas He by donating one electron while bromine can attain electronic configuration like nearest noble gas Kr by accepting one electron. So, Li donates one electron to bromine and forms an ionic bond. Thus, both the elements get stability by attaining electronic configuration like nearest noble gas and form a new compound LiBr.
An Interesting Salt Lithium Bromide (LiBr)
Lithium (Li) is the 3rd element in a series of elements as mentioned in a periodic table. It can chemically combine with the Bromine (Br)element to form a chemical compound called Lithium bromide (Libr). It is a type of salt as sodium chloride (NaCl) but what differs it from other salts is that it is extremely hygroscopic in nature. This property of Lithium bromide makes it a very useful substance in various places. Though it is available naturally due to its large amount of use, it is now being produced artificially by industrial methods. To produce Lithium bromide lithium carbonate and hydrobromic acid are used. Both the compounds are suspended in water to come closer and react. In this mechanism, Lithium Bromide precipitates down in that aqueous solution.
The most popular use of Lithium bromide is its use in Air conditioning systems as a desiccant and rarely in absorption refrigerators as a heat-absorbing salt. The other uses of Lithium bromide include its use as a catalyst for oxidation and hydroformylation of organic compounds or sometimes for their deprotonation and dehydration. In medical science, it is also used for the purification of various steroids that are used for treating ailments or suppressing pain. Lithium bromide is also infamous as a sedative of the early 2oth century. So it can be said that Lithium bromide has some psychoactive properties. Another great use of Lithium bromide is that it is used as a drug to treat bipolar disorder.
Properties of Lithium Bromide
Physical and chemical properties of lithium bromide are listed below –
Its chemical formula is LiBr
Boiling point of lithium bromide is 1265 oC.
Melting point of lithium bromide is 552 oC.
It is a hygroscopic white solid.
Its molar mass is 86.845 g/mol.
Its density is 3.464 g/cm3.
It is soluble in water. Its solubility in water increases, as the temperature increases. For example, its solubility in water is 143 g/100 ml at 0 oC and as the temperature reaches up to 20 oC, its solubility becomes 166.7 g/100ml.
It is also soluble in methanol, ethanol, ether, acetone etc. It is slightly soluble in pyridine.
It is not flammable.
It can dissolve many polar organic compounds such as cellulose.
It is stable in nature and generally, does not react easily.
Its anhydrous form forms cubic crystals like NaCl.
Reaction with chlorine – Lithium bromide reacts with the chlorine molecule and forms lithium chloride salt and bromine gas. Reaction is given below –
Cl2 + 2LiBr → Br2 + 2LiCl
Reaction with silver nitrate – Lithium bromide reacts with silver nitrate and forms lithium nitrate and silver bromide.
Structure of Lithium Bromide
In lithium bromide, an ionic bond is formed by the transfer of an electron from lithium to bromine. As lithium donates an electron so it forms a cation or gets a positive charge Li+. While bromine accepts an electron, it forms an anion or gets a negative charge Br-. The crystal structure of lithium bromide is cubic.
Production of Lithium Bromide
Lithium bromide can be prepared by many methods. A few of them are listed below –
By the reaction of lithium carbonate and hydrobromic acid – Lithium bromide can be prepared by reaction of lithium carbonate with hydrobromic acid. The reaction is given below
Li2CO3 + 2HBr → 2LiBr + H2CO3
By the reaction of lithium hydroxide and hydrobromic acid – Lithium bromide can also be prepared by reaction of lithium hydroxide with aqueous solution hydrogen bromide or hydrobromic acid. The reaction is given below
LiOH + HBr → LiBr + H2O
Uses of Lithium Bromide
Lithium bromide is used in many fields. A few of its uses are listed below –
It is used in air – Conditioning machines as a desiccant due to its hygroscopic nature. It is used with water in absorption chilling in air conditioners.
It is used in the synthesis of many organic compounds.
It is used in pharmaceuticals in the synthesis of many drugs.
It is used to produce many inorganic compounds as well such as lithium chloride etc.
It was used as a sedative in the early 1900s but due to some adverse effects on the heart, doctors stopped using it as a sedative.
Lithium chloride and lithium bromide were used for the treatment of bipolar disorder.
It is used in the synthesis of olefins for catalytic dehydrohalogenation.
It is used in refrigerators as a non - CFC alternative as due to its hygroscopic nature it can easily absorb excess vapor. Thus, it makes the system environmentally friendly.
It is used in emulsions as it is soluble in ether and other organic solvents.
FAQs on Lithium Bromide: Chemical Formula, Structure & Key Uses
1. What is the chemical formula and molar mass of Lithium Bromide?
The chemical formula for Lithium Bromide is LiBr. It is an ionic compound formed from the lithium cation (Li⁺) and the bromide anion (Br⁻). Its molar mass is approximately 86.845 g/mol.
2. What are the main uses of Lithium Bromide?
The primary use of Lithium Bromide is as a desiccant in industrial air conditioning and absorption refrigeration systems. Its key applications include:
- Absorption Refrigeration: It acts as an absorbent, where its strong affinity for water is used to create a cooling cycle.
- Dehumidification: It effectively removes moisture from the air due to its highly hygroscopic nature.
- Organic Synthesis: It serves as a catalyst or reagent in various chemical reactions.
- Medical Applications: Historically, it was used as a sedative, but this use is now rare.
3. What is the crystal structure of Lithium Bromide?
Lithium Bromide (LiBr) has a crystal structure similar to that of sodium chloride (NaCl), known as the rock salt structure. In this cubic crystal lattice, each lithium ion (Li⁺) is octahedrally coordinated by six bromide ions (Br⁻), and each bromide ion is similarly surrounded by six lithium ions.
4. Is Lithium Bromide an ionic or covalent compound?
Lithium Bromide (LiBr) is predominantly an ionic compound. It forms from the electrostatic attraction between the lithium cation (Li⁺) and the bromide anion (Br⁻). However, due to the small size and high polarising power of the Li⁺ ion, LiBr also exhibits some covalent character, as explained by Fajan's rules.
5. What are the key physical and chemical properties of Lithium Bromide?
Key properties of Lithium Bromide (LiBr) include:
- Appearance: It is a white, crystalline, solid powder.
- Hygroscopic Nature: It is extremely hygroscopic, meaning it readily absorbs moisture from the atmosphere, which is why it is used as a desiccant.
- Solubility: LiBr is highly soluble in water and also soluble in organic solvents like methanol, ethanol, and ether.
- Melting and Boiling Points: It has a high melting point of 552°C and a high boiling point of 1265°C, typical of ionic compounds.
6. Why is Lithium Bromide so effective as a desiccant in air conditioning systems?
Lithium Bromide is an effective desiccant due to its strong hygroscopic properties. This means it has a very high affinity for water molecules. In an absorption chiller system, a concentrated LiBr solution readily absorbs water vapour from the evaporator. This absorption process lowers the pressure and temperature, producing the desired cooling effect. The strong ionic forces between Li⁺ and Br⁻ ions effectively attract and hold the polar water molecules.
7. How does the ionic character of Lithium Bromide compare to other lithium halides (LiF, LiCl, LiI)?
According to Fajan's rules, covalent character in an ionic compound increases as the size of the anion increases. For lithium halides, the lithium cation (Li⁺) is constant, while the anion size increases in the order F⁻ < Cl⁻ < Br⁻ < I⁻. Therefore, the covalent character increases accordingly:
- LiF < LiCl < LiBr < LiI
8. How is Lithium Bromide typically prepared?
Lithium Bromide can be prepared through several standard chemical reactions. A common method is the neutralisation reaction between a base and an acid. It can be synthesised by treating an aqueous solution of lithium carbonate (Li₂CO₃) or lithium hydroxide (LiOH) with hydrobromic acid (HBr). The resulting salt solution is then heated to evaporate the water, yielding crystalline Lithium Bromide.
9. Is a solution of Lithium Bromide in water acidic, basic, or neutral?
A solution of Lithium Bromide (LiBr) in water is neutral, with a pH of approximately 7. This is because LiBr is a salt formed from a strong acid (Hydrobromic acid, HBr) and a strong base (Lithium hydroxide, LiOH). In solution, neither the Li⁺ cation nor the Br⁻ anion undergoes significant hydrolysis to alter the concentration of H⁺ or OH⁻ ions.
