# Sodium carbonate

Sodium carbonate identities, hydrate and assay bases, commercial grades, density, and source-specific property limits.

Reviewed: 2026-10-30

Tags: chemicals, carbonates, substances

## Identity and terminology

Tata’s Dense Ash **99000101** lists **1,000–1,100 g/L bulk density**, with packing unspecified. The same sheet gives **2.533 g/cm³ at 25 °C for pure Na₂CO₃**. Bulk volume includes spaces between grains. Anhydrous soda ash is CAS 497-19-8, 105.99 g/mol. Sodium bicarbonate is NaHCO₃, CAS 144-55-8, 84.01 g/mol. [Merck 1.06392](https://www.sigmaaldrich.com/US/en/product/mm/106392) [Sigma-Aldrich S6014](https://www.sigmaaldrich.com/US/en/product/sigald/s6014)

The mono- and decahydrate entries below have formula water, separate from moisture on supplied material.

| Documented form | Formula | CAS number | Molar mass | Primary product reference |
| --- | --- | --- | --- | --- |
| Monohydrate | Na₂CO₃·H₂O | 5968-11-6 | 124.00 g/mol | [Sigma-Aldrich 230952, ACS reagent](https://www.sigmaaldrich.com/US/en/product/sigald/230952) |
| Decahydrate | Na₂CO₃·10H₂O | 6132-02-1 | 286.14 g/mol | [Merck 1.06391, EMSURE](https://www.merckmillipore.com/RE/en/product/mm/106391) |

**Derived composition:** using those rounded molar masses, the theoretical Na₂CO₃ mass fractions are 105.99/124.00 = 85.48% for ideal monohydrate and 105.99/286.14 = 37.04% for ideal decahydrate. The corresponding formula-water fractions are 14.52% and 62.96%. These are stoichiometric descriptions of pure formulas, not measured moisture, assay results or conversion instructions. [Anhydrous identity](https://www.sigmaaldrich.com/US/en/product/mm/106392), [monohydrate identity](https://www.sigmaaldrich.com/US/en/product/sigald/230952), [decahydrate identity](https://www.merckmillipore.com/RE/en/product/mm/106391)

## Commercial form and reporting basis

Tata's Light Soda Ash sheet identifies Na₂CO₃ from its Mithapur facility and reports bulk density 550–720 kg/m³, total alkalinity as Na₂CO₃ ≥99.0%, and volatile matter ≤0.80% **at packaging**. Its impurity limits include chloride as NaCl ≤0.80%, sulfate as Na₂SO₄ ≤0.03%, iron as Fe₂O₃ ≤0.0029%, and water-insoluble matter ≤0.03%. These are supplier specifications; no test methods or assay dry basis are printed in that table. The PDF filename contains 29072024, but the page has no printed issue date. [Tata Light Soda Ash TDS, complete specification table and footer](https://www.tatachemicals.com/upload/pdf/TDS-Light-soda-ash-29072024.pdf)

InoChem's **anhydrous Dense Soda Ash**, document INO-LAB-TDS-001, version 02, issue 01.08.2023, reports Na₂CO₃ ≥99.3% and **equivalent Na₂O ≥58.1%**, both referencing ASTM E359-17. The oxide equivalent is a reporting basis, not a claim that the product contains that mass fraction of free sodium oxide. The sheet also lists NaCl ≤0.2%, Na₂SO₄ ≤0.03%, iron as Fe₂O₃ ≤20 ppm and loss in heating ≤0.20%, referencing the same method designation. Water-insoluble matter ≤0.05% references IS 251:1998-2010. These method citations do not supply the underlying procedures or an uncertainty budget. [InoChem TDS, chemical table](https://inochem.sa/wp-content/uploads/2023/11/TDS-Dense-Soda-Ash.pdf)

Analytical grades use additional bases. Merck 1.06392 specifies ≥99.9% by acidimetry **on dried substance**, with loss on drying ≤1.0% (300 °C test condition). Its chloride limit is expressed as Cl, rather than NaCl. [1.06392 analysis note](https://www.sigmaaldrich.com/US/en/product/mm/106392)

Sigma-Aldrich 230952 lists monohydrate assay ≥99.5% and loss on drying 13.0–15.0%; the displayed assay does not specify a dry basis. [230952 properties](https://www.sigmaaldrich.com/US/en/product/sigald/230952)

Merck 1.06391 lists both decahydrate acidimetric assay 99.0–102.0% and assay **as Na₂CO₃** 36.7–40.0%. Those differently named results are not interchangeable literal mass fractions. [1.06391 analysis note](https://www.merckmillipore.com/RE/en/product/mm/106391)

**Synthesis:** grade, hydration state, analytical basis and impurity species are separate descriptors. Total alkalinity, a salt assay, volatile matter and loss on drying name different reported quantities. A specification limit is distinct from a result on a dated lot certificate. No lot certificate was examined; the displayed manufacturer certificate interfaces did not supply a selected batch.

## Density and physical-property scope

Light and dense soda ash share the carbonate identity. The following values describe different quantities and products, rather than alternative universal densities.

| Quantity and scope | Reported value | Conditions and limitations |
| --- | --- | --- |
| Absolute density of pure Na₂CO₃ | 2.533 g/cm³ at 25 °C | Tata North America January 2022 TDS; explicitly footnoted as a pure-substance property, not product bulk density |
| Bulk density of Tata North America Dense Ash 99000101 | 1000–1100 g/L; also 62.4–68.6 lb/ft³ | Same TDS; packing and method unspecified |
| Bulk density of InoChem Dense Soda Ash | 950–1150 kg/m³ | ASTM D1895-17 B is the named method |
| Density and bulk density of Merck decahydrate 1.06391 | 1.44 g/cm³ at 20 °C; 700–900 kg/m³ bulk | Method and bulk packing unspecified |

Sources: [Tata dense TDS, page 1 and property footnotes](https://www.tatachemicals.com/tata/sites/default/files/2025-11/product-specifications-of-dense-soda-ash.pdf), [InoChem physical table](https://inochem.sa/wp-content/uploads/2023/11/TDS-Dense-Soda-Ash.pdf), [Merck decahydrate properties](https://www.merckmillipore.com/RE/en/product/mm/106391).

**Synthesis:** bulk density includes the powder or granule bed's void space; an absolute solid density describes another volume basis. Neither is solution density. No concentration-dependent solution-density dataset was established here.

## Aqueous and thermal properties

Tata's January 2022 dense TDS reports pH 11.34 for a 1% solution at 25 °C, but does not define the percentage denominator. [Tata dense TDS, page 1](https://www.tatachemicals.com/tata/sites/default/files/2025-11/product-specifications-of-dense-soda-ash.pdf)

Merck 1.06392 instead reports pH 11.16 at **4 g/L, 25 °C**. [Merck 1.06392 properties](https://www.sigmaaldrich.com/US/en/product/mm/106392)

**Synthesis:** these conditioned values describe alkaline solutions; they do not define a unique pH for every carbonate solution or establish bicarbonate/carbonate fractions. No equilibrium constants or speciation model are supplied here.

The Tata TDS gives maximum solubility as **33.2% at 35.4 °C**; its graph labels only “Percent Soda Ash.” The denominator is not explicitly defined. [Tata TDS, pages 1 and 3](https://www.tatachemicals.com/tata/sites/default/files/2025-11/product-specifications-of-dense-soda-ash.pdf)

Merck's anhydrous page lists **212.5 g/L** without a temperature or solvent-versus-solution volume definition in that entry. [Merck properties](https://www.sigmaaldrich.com/US/en/product/mm/106392) The Tata SDS gives 212.5 g/L at 20 °C, also without that denominator distinction. [Tata SDS, section 9](https://www.tatachemicals.com/tata/sites/default/files/2026-03/tata-msds-sodium-carbonate-anhydrous-en.pdf)

**Synthesis:** these entries do not justify converting between g per litre, g per 100 g water and mass percent of saturated solution.

Merck labels the decahydrate's **33 °C** entry “Elimination of water of crystallisation.” [Decahydrate properties](https://www.merckmillipore.com/RE/en/product/mm/106391) The anhydrous page lists **851 °C (literature)** as melting point. [Anhydrous properties](https://www.sigmaaldrich.com/US/en/product/mm/106392)

**Synthesis:** loss of hydrate water and anhydrous melting are different events. The Tata SDS separately lists melting at **854 °C** and decomposition at **400 °C**, without measurement conditions or explanation. [Tata SDS, section 9](https://www.tatachemicals.com/tata/sites/default/files/2026-03/tata-msds-sodium-carbonate-anhydrous-en.pdf) These unresolved source differences do not establish a decomposition onset, phase sequence or thermal schedule.

## Safety-document and evidence limits

Tata North America's SDS, printed revision **4/1/23**, classifies the substance under U.S. OSHA HazCom 29 CFR 1910.1200 as Eye Irritation Category 2A, H319. Section 3 lists ≥99% sodium carbonate, a composition disclosure rather than a lot assay. Section 9's bulk-density heading says **g/L**, but dense-grade values are **0.9–1.1**: this conflicts with the TDS's 1000–1100 g/L and remains unresolved. No corrected unit is assumed. The SDS URL's 2026-03 folder is not its revision date. [Tata SDS, sections 1–3 and 9](https://www.tatachemicals.com/tata/sites/default/files/2026-03/tata-msds-sodium-carbonate-anhydrous-en.pdf)

This dated regional classification is not a global compliance conclusion. Manufacturer web pages were consulted on October 30, 2026 PDT; they have no fixed specification revision printed in the cited entries. The evidence does not establish current lot composition, formulation compatibility, customer capability, application performance or an exhaustive hydrate phase diagram. Product sheets, SDS disclosures and calculated formula fractions retain their separate scopes.

## Related reference

[Surface-finishing processes](../../processes/finishing/index.md)