Bicarbonates

Introduction

During the process of deprotonation of carbonic acid, an intermediate polyatomic anion is formed. This anion is called bicarbonate anion. It is represented by the chemical formula $\mathrm{HCO_{3}^{-}}$. The terminology of bicarbonate was given by an English chemist named William Hyde Wollaston in 1814. Bicarbonate ions are also referred to as hydrogencarbonate in IUPAC nomenclature. Being anion bicarbonate carries a negative charge. It is an amphiprotic molecule. Amphiprotic species are species which can react with both acids and bases and possess acidic and basic properties. The structure of bicarbonate is similar to that of nitric acid. This explains the isoelectronic temperament of bicarbonate with nitric acid.

Structural Relationship Between Bicarbonate Anion and Carbonic Acid

The structure of bicarbonate ions consists of a central carbon around arranged in a trigonal planar geometry along with one oxygen atom, one oxygen ion and a hydroxyl group. The structure of carbonic acid, on the other hand, has the same trigonal planar geometry but it has two hydroxyl groups and one oxygen atom attached via a double bond. The conjugate acid of bicarbonate is a carbonate ion whereas the conjugate base of bicarbonate is carbonic acid. Therefore, carbonic acid and bicarbonate anion can be interconverted into each by elimination or addition of hydrogen.

Applications of Bicarbonates

One of the most important applications of bicarbonate ions includes the regulation of carbon dioxide via a bicarbonate buffer system. The function of bicarbonates in this system is to maintain extracellular carbon dioxide. The bicarbonate buffer system is the main extracellular buffer system. The carbon dioxide produced during tissue metabolism is removed by the bicarbonate buffer system. The bicarbonate ions act as proton acceptors in the process. The role of proton donors is assigned to carbonic acid. The bicarbonate system can alter the pH of the blood.

$$\mathrm{H_{2}CO_{3}+H_{2}O\rightleftharpoons HCO_{3}^{-}+H^{+}}$$

The application of various bicarbonates not only depends on the anion but also on the cation that constitutes the compound.

Sodium Bicarbonate

Sodium bicarbonate, also known as sodium hydrogencarbonate, is an important component of many delicacies. Commonly known as baking soda or cooking soda or bicarbonate of soda is an inorganic salt that has a wide range of applications. Sodium bicarbonate was first synthesised in a laboratory by French chemist Nicholas Leblanc in 1791. It is extracted from a naturally occurring mineral called nahcolite or thermokalite. The decahydrate naturally occurring form of sodium bicarbonate is called natron. The chemical formula of baking soda is $\mathrm{NaHCO_{3}}$.

Synthesis

The industrial synthesis of sodium bicarbonate involves the reaction of sodium carbonate with carbon dioxide and water. This reaction yields sodium bicarbonate as a white solid precipitate.

$$\mathrm{Na_{2}CO_{3}+CO_{2}+H_{2}O\to 2NaHCO_{3}}$$

Another preparation method involves the reaction of sodium chloride, ammonia and carbon dioxide in the presence of water. This is called Solvay's process.

$$\mathrm{NH_{3}+H_{2}O+CO_{2}\to NH_{4}HCO_{3}}$$

$$\mathrm{NH_{4}HCO_{3}+NaCl\to NaHCO_{3}+NH_{4}Cl}$$

Properties of Sodium Bicarbonates

The properties of sodium bicarbonate are listed below

• It is a white crystalline solid.

• It has a melting point of 50 degrees Celsius.

• It has a boiling point of 851 degrees Celsius.

• It is highly soluble in methanol and acetone.

• It is insoluble in ethanol.

• It has a molecular mass of 84 grams per mole.

• It is alkaline in water and acts as a weak base.

$$\mathrm{NaHCO_{3}+H_{2}O\to H_{2}CO_{3}+NaOH}$$

• It has a pH of 8.31.

• It is an amphoteric compound.

$$\mathrm{NaHCO_{3}+HCl\to H_{2}CO_{3}+NaCl}$$

$$\mathrm{NaHCO_{3}+NaOH\to Na_{2}CO_{3}+H_{2}O}$$

• It undergoes thermal decomposition at around 80-100 degrees Celsius.

$$\mathrm{2NaHCO_{3}\to Na_{2}CO_{3}+H_{2}O+CO_{2}}$$

• It is sparingly soluble in water.

Applications of Sodium Bicarbonate

Sodium bicarbonate has a wide range of applications in cooking, pyrotechnics, agriculture, pharmaceuticals, medicine, etc. Some of these applications are listed below

• In cooking and baking, sodium bicarbonate is used as a raising agent (or leavening agent). It is often used with acidic material to trigger the reaction that produces carbon dioxide.

• It is the main component in the composition of fireworks.

• It is used to decrease the rate of combustion reactions.

• It can be used as a disinfectant.

• It is used as a fire extinguisher.

Potassium Bicarbonate

Just like sodium bicarbonate, potassium bicarbonate is also a commercially important compound. Potassium bicarbonate is an inorganic salt of cationic potassium ion and anionic bicarbonate ion. According to IUPAC nomenclature, it is known as potassium hydrogen carbonate. Both sodium bicarbonate and potassium bicarbonate were once referred to as saleratus which means aerated salts. The chemical formula of potassium acid carbonate is $\mathrm{KHCO_{3}}$.

Properties of Potassium Bicarbonate

Some of these properties are listed below

• It is a white solid.

• It can be found in powdered and crystalline forms.

• It is alkaline.

• It has a molecular mass of 100.115 grams per mole.

• It does not boil. It decomposes at a temperature of 120 degrees Celsius.

• It has a melting point of 292 degrees Celsius

• It acts as a weak base.

• It has a pH of 8.2.

• It is highly soluble in water.

• It is insoluble in ethanol.

• It is odourless.

• It is amphoteric.

Synthesis

The manufacturing process of potassium bicarbonate involves a reaction between an aqueous solution of potassium carbonate and carbon dioxide.

$$\mathrm{K_{2}CO_{3}+H_{2}O+CO_{2}\to 2KHCO_{3}}$$

The potassium bicarbonate produced in this reaction is decomposed to synthesize a highly pure form of potassium carbonate.

$$\mathrm{2KHCO_{3}\to K_{2}CO_{3}+CO_{2}+H_{2}O}$$

Applications of Potassium Bicarbonate

The applications of potassium bicarbonate are similar to sodium bicarbonate.

• It is used as a leavening agent in baking, cooking and beverages as it is a good source of carbon dioxide.

• It is used to regulate pH in medicines.

• It is used as an additive in wine production.

• It is used in fire extinguishers.

• It is used for the neutralization of acidic soil in agriculture.

Conclusion

To summarize, bicarbonates are extensively used inorganic compounds. These compounds contribute to many metabolical functions such as respiration, excretion, regulation, etc. The non-toxic nature of these compounds is ideal for producing baked and cooked goods. Not just for cooking, they can be used as a cleaning agent and odourcontrolling agent in households and industries. Cold beverages such as coke contain bicarbonates to produce the bubbling effect. Potassium bicarbonate is generally used to produce low-sodium food material. The alkaline nature of bicarbonates is utilized in various buffers of drugs. The production of bicarbonates is generally done by taking their respective carbonates as substrates.

FAQs

Qns. 1. What is the structure of sodium bicarbonate?

Ans. The structure of sodium bicarbonate is given below

Qns. 2. What is the structure of potassium bicarbonate?

Ans. The structure of potassium bicarbonate is given below

Qns. 3. Which bicarbonate is used in antacids?

Ans. Sodium bicarbonate is used in antacids. It produces carbon dioxide in reaction with stomach acid which can treat indigestion.

Qns. 4. What is the difference between washing soda and baking soda?

Ans. Washing soda is sodium carbonate ($\mathrm{Na_{2}CO_{3}}$) and baking soda is sodium bicarbonate($\mathrm{NaHCO_{3}}$).

Qns. 5. Why alkaline earth metals (group 2) bicarbonates are sparingly soluble in water?

Ans. Alkaline earth metals (group 2) bicarbonates are sparingly soluble in water because of their high lattice energies.