“Sodium carbonate, dense” and “soda ash, dense” name one material. This page covers the identity side: which names, formulas and registry numbers refer to the same substance, what “dense” actually specifies, and how to write a purchase specification that cannot be met by the wrong grade. For properties, applications and the reason dense grade dominates glass manufacture, see the dense soda ash page.
Substance identity
| Field | Value |
|---|---|
| Systematic name | Sodium carbonate |
| Formula | Na2CO3 |
| CAS number | 497-19-8 |
| PubChem CID | 10340 |
| EC number | 207-838-8 |
| Molar mass | 105.99 g/mol |
| Sodium content, calculated | 45.98 / 105.99 = approx. 43.4 % Na |
| Carbonate content, calculated | approx. 56.6 % CO3 |
Names in circulation for this exact material: soda ash dense; dense ash; sodium carbonate anhydrous, dense; calcined soda; disodium carbonate. All refer to the same CAS number. “Washing soda” usually means the decahydrate and should not be used for this product.
Names that are not this material: sodium bicarbonate (NaHCO3, CAS 144-55-8) is a different substance, not a grade of soda ash; sodium sesquicarbonate and trona are double salts; the monohydrate and decahydrate are distinct hydrated substances with their own CAS numbers and lower Na2CO3 content per tonne.
Specification
What “dense” specifies, and what it does not. Typical commercial values, not guaranteed limits.
| Specification element | Dense grade | Comment |
|---|---|---|
| Bulk density | approx. 0.90–1.10 t/m3 | the only parameter that actually defines the grade |
| Particle size distribution | majority typically 0.15–0.85 mm | request the sieve analysis, not a single mean value |
| Assay, total alkali as Na2CO3 | 99.2 % min typical, dry basis | identical basis to light grade — assay does not distinguish them |
| Loss on heating | typically ≤ 0.5–1.0 % | |
| Iron as Fe2O3 | typically ≤ 0.0035 % | |
| NaCl | typically ≤ 0.3–0.8 % | route-dependent |
Writing a specification that works. A specification reading “sodium carbonate, 99.2 % min” is satisfied by light ash. To obtain dense grade you must state, as pass/fail criteria: (1) a bulk density range with the measurement method named, (2) a sieve analysis with limits at named apertures, and (3) a fines limit. Bulk density figures are method-sensitive — loose poured and tapped values differ materially — so name the method, or the number is unverifiable.
Properties
Physical constants are those of sodium carbonate and are independent of grade: melting point approx. 851 °C; true density approx. 2.53–2.54 g/cm3; solubility approx. 21.5 g/100 g water at 20 °C; pH of a 1 % solution approx. 11.3–11.6. Dissolution of the anhydrous salt is exothermic.
Grade-dependent behaviour: dense grade dissolves more slowly than light at equal agitation, because of its lower specific surface area. Where rapid make-up of a carbonate solution is the objective, this is a disadvantage rather than a neutral difference.
Applications
Application scope is that of sodium carbonate generally; the dense grade is selected where bulk mechanical handling, low dust and resistance to segregation govern — principally soda-lime glass batch, and metallurgical and mineral-processing duties fed by mechanical conveyors. Detailed treatment, including why dense grade suits glass batch, is on the dense soda ash page. Where the material is dissolved, the light grade is normally specified.
Handling and storage
Alkaline; irritating to eyes, skin and respiratory tract as dust or solution; the supplier’s safety data sheet governs. Hygroscopic — absorbs atmospheric moisture and carbon dioxide, cakes, and loses assay slowly on prolonged exposure. Keep sealed, dry, off the floor, out of condensation cycles.
Incompatible with acids (rapid CO2 evolution and heat) and with aluminium and zinc in the presence of moisture (alkaline attack, hydrogen evolution). Do not use aluminium handling equipment.
Dense grade is markedly better than light grade for silo storage: it flows, bridges less, and dusts far less at transfer points. Silo and feeder geometry sized for dense grade should not be assumed to work with light.
Notes
- This page and the dense soda ash page describe the same product. Under the accepted plan this URL is a 301, not a page. If both were ever published, one would have to carry
rel="canonical"pointing to the other. - Assay alone never distinguishes dense from light. Every grade dispute traced to this cause starts with a specification that omitted bulk density.
- Substance identity for regulatory purposes (inventory listings, SDS, transport documentation) follows CAS 497-19-8 regardless of grade. The grade is not part of the substance identity.