Sodium Carbonate

Sodium Carbonate Na₂CO₃

Sodium carbonate also called washing soda or soda ash is an inorganic compound or salt with the chemical formula Na₂CO₃. In pure form, sodium carbonate is a white crystalline powder. Sodium carbonate produces an alkaline solution that contains carbonic acid and sodium hydroxide when dissolved in water. Sodium carbonate uses widely for making detergents and soaps, paper, glass, and brick industry, and for modifying pH and softening water. Washing soda or sodium carbonate is now exclusively manufactured by the Solvay process where sodium chloride, carbon dioxide, and ammonia react to form sodium bicarbonate or baking soda. Baking soda is converted to sodium carbonate and washing soda when heating and recrystallization.

One common source of washing soda or sodium carbonate is the ashes of burned plants. Therefore, it is sometimes called soda ash. It is a strong base with a pH of about 11. Therefore, it is used as an antacid because it is non-corrosive and safer to handle.

Sodium carbonate in washing soda softens water. Therefore, it helps other cleaning ingredients lift soil from fabrics and suspend the soil in the wash water. It is also used for making the sodium compound borax. In laboratory and analytical chemistry, it is used to standardize an acid and an analytical reagent.

Washing Soda

Washing soda is the most common hydrate of sodium carbonate (Na₂CO₃) that contains 10 molecules of water of crystallization. It commonly occurs as a crystalline decahydrate with the chemical formula Na₂CO₃·10H₂O. However, washing soda readily effloresces to form a white powder, the monohydrate (Na₂CO₃·H₂O).

The compound Na₂CO₃ obtained by heating baking soda recrystallizes to form washing soda.

Na₂CO₃ (s) + 10 H₂O (l) → Na₂CO₃.10H₂O (s)

Washing soda and baking soda are two closely related compounds found in mineral trona. These two compounds can be used together in laundry to remove stains.

Sodium carbonate occurs in three different hydrated forms and an anhydrous form.

• Washing Soda: It contains ten water molecules with the chemical formula Na₂CO₃·10H₂O
• Sodium carbonate heptahydrate: It contains seven water molecules with the chemical formula Na₂CO₃·7H₂O
• Thermonatrite: It is a monohydrate form of Na₂CO₃ with the chemical formula Na₂CO₃·H₂O
• Anhydrous salt: Anhydrous Na₂CO₃, also known as calcined soda is formed by heating the hydrates.

Structure

The pure form of sodium carbonate is a white crystalline powder and is readily dissolved in water. Each molecule of sodium carbonate contains two unipositive sodium cations and one bi-negative carbonate anion.

Two unipositive sodium cations and one bi-negative carbonate anion bind together by ionic bonding to form a Na₂CO₃ molecule. Therefore, Na₂CO₃ is a neutrally charged molecule that contains two sodium, one carbon, and three oxygen atoms.

Properties

The pure form of sodium carbonate is a white crystalline solid that forms an alkaline solution when dissolved in water. It is the one of metal carbonate that dissove in water. It is freely soluble in water but sparingly soluble in ethanol and insoluble in acetone.

IUPAC name	Sodium carbonate
Other names	Soda ash Washing soda Soda crystals Sodium trioxocarbonate
Chemical formula	Na2CO3 for anhydrous carbonate Na2CO3·10H2O for washing soda
Appearance	Pure form is a white crystalline solid with an odorless and hygroscopic nature
Molecular Weight/ Molar Mass	105.9888 g/mol (carbonte) 286.1416 g/mol (washing soda)
Density	2.54 g/cm3 (anhydrous) 1.46 g/cm3 (washing soda)
Boiling Point	1600 °C
Melting Point	851 °C
Solubility	Freely soluble in water and glycerol but sparingly soluble in ethanol, and insoluble in acetone, carbon disulfide, liquid ammonia, etc.
Viscosity	3.4 cP at 887 °C
Heat capacity	112.3 J mol−1 K−1
CAS Number	497-19-8 (Pure form) 6132-02-1 (washing soda or decahydrate form)

Washing soda has the property to remove dirt and grease from dirty clothes. Therefore, it is called washing soda. It is a diazonium salt of carbonic acid with the chemical formula Na₂CO₃.

Chemical Properties

Anhydrous sodium carbonate is a stable chemical compound towards heat because it melts at 851 °C without any decomposition.

Sodium carbonate forms an alkaline solution that contains carbonic acid and sodium hydroxide when dissolved in water.

Na₂CO₃ + 2H₂O→ H₂CO₃ + 2Na⁺ + 2OH^–

The aqueous solution of sodium carbonate absorbs carbon dioxide from the air to form sodium bicarbonate.

Na₂CO₃ (aq) + H₂O + CO₂ (g) → 2NaHCO₃ (aq)

Sodium carbonate reacts with weak vegetable acids present in lime juice and hydrochloric acid to liberate carbon dioxide.

Na₂CO₃ + 2H⁺ → 2Na⁺ + H₂O + CO₂

Na₂CO₃ + 2HCl → 2NaCl + H₂O+ CO₂

How to Make Sodium Carbonate?

Sodium carbonate can be made mainly by the Solvay process or from trona and nahcolite ores. The Solvay process is not used in the United States because a large amount of sodium carbonate ores (trona) is deposited in Wyoming, US.

Solvay Process

In 1861, the Belgian industrial chemist Ernest Solvay developed a process to make sodium carbonate from sodium chloride, ammonia, water, and carbon dioxide. Therefore, it is called the Solvay process after the name of the discoverer.

The Solvay process goes to the stages given in the diagram below.

Ammoniation of Brine

Ammoniation of brine is a process where brine solution can be saturated by ammonia gas to form ammoniacal brine. Therefore, the solution contains Na⁺, Cl⁻, NH₄⁺, and OH⁻ ions sent to the Solvey tower.

Formation of calcium oxide and carbon dioxide from limestone

Kilns are fed with a mixture of limestone and coke and heated. carbon prest in coke burns in the air to form carbon dioxide.

C + O₂ → CO₂

The heat produced during the combustion of coke decomposes limestone to calcium oxide and carbon dioxide.

CaCO₃ → CaO + CO₂

The gas containing carbon dioxide is sent to the Solvey tower and calcium oxide is used for the regeneration of ammonia gas.

Formation of solid sodium bicarbonate

In Solvey Tower, carbon dioxide from Kilns and heated sodium bicarbonate reacts with dissolved ammonia to form ammonium bicarbonate.

CO₂ + NH₃ + H₂O → NH₄HCO₃

Therefore, after the addition of brine (sodium chloride), the solution containing NH₄⁺ and HCO₃^– ion forms a precipitation of least soluble NaHCO₃ and soluble NH₄Cl.

NaCl + NH₄HCO₃ → NaHCO₃ + NH₄Cl

Separation of solid sodium bicarbonate

The suspension from the least soluble NaHCO₃ and soluble NH₄Cl is separated by filtration to collect solid sodium bicarbonate. Ammonium chloride is further used for the regeneration of ammonia.

Formation of sodium carbonate

Sodium bicarbonate can be heated in rotating ovens at 450 °K, it is converted to sodium carbonate, carbon dioxide, and water. The produced carbon dioxide is sent to the Solvay tower for the formation of solid sodium bicarbonate.

2NaHCO₃ → Na₂CO₃ + H₂O + CO₂

Formation of calcium hydroxide

Quicklime or calcium oxide is generated from limestone slaked with excess water from the milk of lime or calcium hydroxide because it is used for the regeneration of ammonia.

CaO + H₂O → Ca(OH)₂

Regeneration of ammonia

Calcium hydroxide obtained from the previous step mixed with ammonium chloride obtained after filtration can heated for the regeneration of ammonia gas.

Ca(OH)₂ + 2NH₄Cl → 2NH₃ + CaCl₂ + 2H₂O

The ammonia gas can be recovered and sent for ammoniation of brine. Only one by-product calcium chloride is generated during the whole process.

From Trona and Nahcolite Ores

Trona is the primary source of sodium carbonate in the US, with the chemical formula Na₂CO₃.NaHCO₃.2H₂O. The solid form of trona has been mined and heated to drive off carbon dioxide and make sodium carbonate.

2Na₂CO₃.NaHCO₃.2H₂O + Heat → 3Na₂CO₃ + CO₂ + 5H₂O

The other ore, nahcolite is a soft mineral or naturally occurring form of sodium bicarbonate (NaHCO₃). Therefore, it can be mined and heated to make sodium carbonate.

Washing Soda vs Baking Soda

Baking soda and washing soda are chemically similar compounds but differ in their chemical composition.  Washing soda also called sodium carbonate contains two sodium, one carbon, and three oxygen atoms along with ten water molecules while baking soda contains one sodium, one hydrogen, one carbon, and three oxygen atoms. Therefore, the chemical formula of washing soda is Na₂CO₃.10H₂O while baking soda is NaHCO₃.

Washing soda contains one carbonate ion in its structure but baking soda contains one bicarbonate ion in its structure. Washing soda and baking soda can be used together in laundry to remove stains from clothes.

Making Washing Soda from Baking Soda

Heating baking soda at home in an oven releases carbon dioxide and water to form dry sodium carbonate or washing soda.

1. Take a small amount of baking soda in a shallow baking dish or on a shallow baking sheet.
2. Place the dish or sheet in a 400 °F oven for one hour.
3. Stir and spread the baking soda on a baking sheet or dish.
4. Bake for an additional hour at 400°F and stirring every half hour.
5. Obtained Na₂CO₃ by heating baking soda recrystallizes after cooling to form washing soda.
6. Obtained washing soda stored in an airtight container because washing soda readily effloresces to form a white powder, the monohydrate (Na₂CO₃·H₂O).

Uses of Sodium Carbonate

Sodium carbonate is a commonly used chemical compound for glass, soap, and paper industries. It is also a common cleaning agent that uses in houses and laundries for making detergents and softening water.

Washing Soda in the Laundry

Washing soda is a natural cleaning agent used in laundry to remove stains from clothes and boost the cleaning power of detergent. In water, washing soda forms a presoaking solution for tough stains such as grease, blood, tea, and coffee.

It has properties of sofinification where it converts fats and grease to water-soluble salts. Therefore, powdered-form washing soda is widely used to make various dry soaps and detergents. It also removes the permanent hardness of water that is used in the laundry cleaning process.

Sodium Carbonate in Water Softening

Sodium carbonate is a good water-softening agent because it is a highly water-soluble salt that converts the chlorides and sulfates of calcium and magnesium into their respective carbonates.

CaCl₂ + Na₂CO₃ → CaCO₃ + 2 NaCl

MgSO₄ + Na₂CO₃ → MgCO₃ + Na₂SO₄

The calcium and magnesium salts form insoluble solid precipitates upon treatment with Na₂CO₃. Hard water softens because it does not contain dissolved calcium and magnesium ions. Therefore, it removes the permanent hardness of water.

Washing Soda for Cleaning

Washing soda is a useful cleaning agent that is used for cleaning home appliances, kitchens, drains, bathrooms, etc. It is a highly alkaline substance that can act as a solvent to remove stains and greasy buildup.

• Washing soda is a useful cleaning agent for the kitchen. It can remove greasy buildup from pots, oven racks, and pans used in the kitchen.
• It is also used for cleaning the drum in the washing machine.
• Washing soda may also used for removing coffee and tea stains from ceramic items and plastic storage containers.
• Washing soda along with boiling water can be used to unclog drains.
• It is mixed with water in a spray bottle and sprayed the mixture to control aphids, whiteflies, and possibly black spots on roses.

Other Uses of Sodium Carbonate

• For making glass, the heavy or dehydrating form of solid sodium carbonate is used as a flux for melting silica or sand.
• Washing soda is a useful agent for making natural dyes from plants.
• Sodium carbonate may also used to make borax, sodium phosphate, and many other sodium compounds.
• In the brick industry, it is used as a wetting agent.
• It is an abrasive and foaming agent to make toothpaste.
• It is also used as a water softener and pH modifier in chemical laboratories.
• When an aqueous solution of sodium carbonate spreads on plants, it helps to control outdoor pests.

Toxicity

Washing soda or sodium carbonate is not a toxic chemical compound if not swallowed or inhaled. However, it causes corrosive effects on the human body and may be dangerous to the gastrointestinal system if swallowed. The inhalation of this compound can cause many health issues such as respiratory tract irritation, breathing problems, coughing, etc.

Frequently Asked Questions

What is Sodium Carbonate?

Sodium carbonate is an inorganic compound or diazonium salt of carbonic acid with the chemical formula Na₂CO₃. Therefore, it contains two sodium cations and one carbonate anion in its structure. Washing soda is the most common hydrate of sodium carbonate that contains 10 molecules of water with chemical formula Na₂CO₃.10H₂O.

Sodium carbonate is a highly alkaline substance that uses as a cleaning agent in houses, kitchens, and laundries for making detergents and softening water. In soap, paper, and glass industries, Na₂CO₃ is an important ingredient for making soaps, paper, and glasses.

What is Washing Soda Used For?

Washing soda is used mainly for removing stains in our clothes, pots, and pans at home, laundry, and kitchen. Washing soda also softens water that we use for laundry or cleaning. It is a commonly used chemical compound for glass, soap, and paper industries.

Is Washing Soda the Same as Baking Soda?

No, washing soda is chemically different from baking soda because washing soda contains two sodium cations, one carbonate anion, and 10 water molecules while baking soda contains one sodium cation and one bicarbonate anion. Therefore, the chemical formula of washing soda is Na₂CO₃.10H₂O while baking soda is NaHCO₃.

Is Soda Ash Soluble in Water?

Yes, soda ash dissolves in water and crystallizes to form washing soda. It is one of the metal carbonates that is highly soluble in water. The solution of soda ash is alkaline in nature and turns red litmus paper to blue.