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Glass, soap and paper all need sodium carbonate, also called soda ash or, as its hydrate, washing soda. In the mid-1800s it was made by a complex and costly route. A young Belgian with little formal education made a better route work at scale, and soda ash made from salt and limestone is still a large share of world supply. This post covers who Ernest Solvay was, how the process works, a worked mass calculation, and what you can take from his approach.
Who was Ernest Solvay?
The *Dictionary of Scientific Biography* entry on Solvay records that he was born at Rebecq-Rognon, near Brussels, on 16 April 1838, and died in Brussels on 26 May 1922. After a modest education at local schools, he worked in his father's salt business. At 21 he joined his uncle in managing a gasworks in Brussels, where his task was finding better ways to concentrate ammonia liquors.
In 1861, the entry says, he noticed how easily ammonia, salt solution and carbon dioxide react to form sodium hydrogencarbonate. He did not know that the reaction had been known for about fifty years, or that several industrial chemists had already tried and failed to use it at scale.
What problem was he solving?
Demand for soda ash came from glass and soap makers, and at the time it was met by the Leblanc process, which the same entry calls "economically unstable and chemically complex". The ammonia-soda reaction was simple on paper. The difficulty was engineering: ammonia is expensive, so losing it ruins the economics, and mixing a gas thoroughly with a liquid on a large scale is hard.
Solvay's knowledge of salt and ammonia from his family's businesses helped. With his brother Alfred he set up a small works in Brussels in 1861. In 1863 the brothers built a factory at Couillet, near Charleroi, and production started in 1865. According to the entry, his key contribution was a carbonating tower in which ammoniacal brine could be mixed thoroughly with carbon dioxide. He patented every stage but licensed the process abroad, and by 1890 there were plants across Europe, in Russia and in the United States.
How does the Solvay process work?
Your NCERT Class 10 Science chapter on acids, bases and salts (reprint 2026-27) gives the central reaction for making baking soda from salt:
NaCl + H₂O + CO₂ + NH₃ → NH₄Cl + NaHCO₃
It then shows that heating sodium hydrogencarbonate gives sodium carbonate:
2NaHCO₃ → Na₂CO₃ + H₂O + CO₂
and that recrystallising sodium carbonate gives washing soda, Na₂CO₃·10H₂O.
The full industrial cycle adds steps that make it economical:
Make CO₂: heat limestone, CaCO₃ → CaO + CO₂.
Carbonate the ammoniacal brine (the reaction above). NaHCO₃ is only slightly soluble in the cold solution, so it comes out as a solid and is filtered off.
Heat the NaHCO₃ to get Na₂CO₃. The CO₂ released goes back to step 2.
Recover the ammonia: slake the lime, CaO + H₂O → Ca(OH)₂, then 2NH₄Cl + Ca(OH)₂ → 2NH₃ + CaCl₂ + 2H₂O. The ammonia goes back to step 2.
Add these up and ammonia cancels out completely. The net reaction is:
2NaCl + CaCO₃ → Na₂CO₃ + CaCl₂
Worked example: how much soda ash from a tonne of salt?
Problem. Using the net reaction, find the maximum mass of Na₂CO₃ and of CaCl₂ from 1000 kg of NaCl. Use Na = 22.990, Cl = 35.45, C = 12.011, O = 15.999, Ca = 40.078.
Molar masses: NaCl = 58.44 g/mol; Na₂CO₃ = 2(22.990) + 12.011 + 3(15.999) = 105.99 g/mol; CaCl₂ = 40.078 + 2(35.45) = 110.98 g/mol.
Moles of NaCl: 1,000,000 g ÷ 58.44 g/mol = 17,112 mol.
The equation uses 2 NaCl per Na₂CO₃, so Na₂CO₃ = 17,112 ÷ 2 = 8,556 mol.
Mass of Na₂CO₃ = 8,556 × 105.99 ≈ 906,800 g ≈ 907 kg.
CaCl₂ is also 8,556 mol, so its mass is 8,556 × 110.98 ≈ 949,500 g ≈ 950 kg.
So a tonne of salt gives at most about 0.91 tonnes of soda ash and about 0.95 tonnes of calcium chloride. That large by-product is one reason the USGS Mineral Commodity Summaries 2025 notes that synthetic soda ash "generates environmental wastes" and normally uses more energy than soda ash mined from natural trona. The same report estimates world synthetic production in 2024 at 49 million tonnes, out of about 73 million tonnes in total.
Common mistakes:
Forgetting the 2:1 ratio of NaCl to Na₂CO₃ and getting 1813 kg, which would break conservation of sodium.
Treating ammonia as a reactant in the net equation. It is recycled.
Writing Na₂CO₃ when the precipitate is NaHCO₃. The carbonate only forms on heating.
Is this on the syllabus?
The current NCERT Class 11 Chemistry books (reprint 2026-27) no longer have an s-block chapter: Part I runs from basic concepts to equilibrium, and Part II from redox to hydrocarbons. The baking soda reaction remains in Class 10. The JEE (Advanced) 2026 syllabus still lists the preparation, properties and uses of sodium carbonate and sodium hydrogencarbonate under s-block elements. Check your own exam's current document. For the board-level chemistry, see our post on acids, bases and salts in Class 10, and for the JEE Advanced side, our s-block elements guide.
What did he do with the money?
The International Solvay Institutes say that after the 1911 Solvay Council on "Radiation and the Quanta", chaired by Hendrik Lorentz, Ernest Solvay founded the International Solvay Institute for Physics in 1912. The Solvay conferences went on to gather the founders of quantum theory.
What can a student learn from Solvay?
Knowing a reaction is not the same as making it work. The chemistry was decades old; his contribution was the tower and the recycling.
Use what you already know. His background in salt and ammonia let him see the real obstacles.
Track every atom. The worked example shows why recycling ammonia and CO₂ decides the whole design.
When a stoichiometry problem goes wrong at the ratio step, the Fermi Problem Library has worked problems with a step-by-step solver that explains the reasoning, so you can see where your mole ratio slipped.
Try this: how much CaCO₃ is used for 1000 kg of NaCl? (Answer: about 856 kg.)
