Substance profile
Fluorosulfuric acid
Fluorosulfuric acid is a colorless liquid; reddish-brown color with acetone.
01 · Identification
What Fluorosulfuric acid is
Fluorosulfuric acid is a colorless liquid; reddish-brown color with acetone. Its molecular formula is FHO3S and its molecular weight is 100.07 g/mol. It boils at 163 °C, melts at -89 °C.
Under the GHS it carries the signal word Danger. It is classed as corrosives.
02 · Identifiers
Fluorosulfuric acid identifiers and molecular data
Fluorosulfuric acid CAS number and EC number
Fluorosulfuric acid molecular formula and molecular weight
Other names for Fluorosulfuric acid
- fluorosulphonic acid
03 · GHS classification
Fluorosulfuric acid hazard classification
Harmonised classification under CLP Annex VI. This is the legally binding classification in the EU; other jurisdictions may differ.
Fluorosulfuric acid pictograms and signal word
Fluorosulfuric acid hazard class and category
| Hazard class | Category | From code | Pictogram |
|---|---|---|---|
| Acute toxicity - inhalation GHS chapter 3.1 | Category 4 | H332 | GHS07 |
| Skin corrosion/irritation GHS chapter 3.2 | Category 1A or 1B or 1C | H314 | GHS05 |
Where two values are shown with “or”, the hazard statement is shared by more than one category or by more than one class, and the code alone does not say which. H272, for example, belongs to oxidising liquids and to oxidising solids — the physical state decides. The binding answer for a specific entry is in the CLP Annex VI table itself.
Fluorosulfuric acid hazard statements (H-codes)
| Code | Hazard statement |
|---|---|
| H332 | Harmful if inhaled. |
| H314 | Causes severe skin burns and eye damage. |
This page lists only the codes assigned to Fluorosulfuric acid. The full reference lives on the hazard statements hub, the precautionary statements hub and the GHS pictograms hub.
Safety Data Sheet
Getting an SDS for Fluorosulfuric acid
A Safety Data Sheet is written for a product, not for a substance: the supplier of the grade you actually buy issues it, so two suppliers of Fluorosulfuric acid issue two different sheets. That is why there is no single authoritative SDS for a substance to download — what there is, is the job of collecting the sheets for the products you hold and keeping them current as suppliers revise them.
04 · Precautionary statements
Fluorosulfuric acid precautionary statements
CLP Annex VI assigns 8 precautionary statements to Fluorosulfuric acid. They are grouped the way a label groups them: what to do before handling, what to do when something has already happened, how to store it and how to dispose of it.
Prevention
What to do before and during handling so the hazard never happens.
Response
What to do once exposure, spillage or fire has already happened.
Reading the notation. … is a blank the supplier fills in — not a truncated sentence.· [square brackets] mark a part printed only when it applies.
05 · Names in the regulation
Fluorosulfuric acid name in 23 EU languages
CLP Annex VI Part 3 is published in every language edition of the regulation, and the identification column is written out in each of them. Nothing below is translated by us: each line is the name as that edition prints it. Under Art. 18(2) the substance name from Annex VI is a lawful product identifier, so this is the wording to put on a label going to that market — and where the cell lists several designations, any one of them qualifies.
| Language | Name in CLP Annex VI Part 3 |
|---|---|
| Bulgarian български | флуоросулфонова киселина |
| Spanish español | Ácido fluorosulfónico |
| Czech čeština | fluorosírová kyselina |
| Danish dansk | fluorsulfonsyre |
| German Deutsch | Fluorsulfonsäure |
| Estonian eesti | fluorosulfoonhape |
| Greek ελληνικά | φθοροσουλφονικό οξύ |
| English English | fluorosulphonic acid |
| French français | This edition prints another entry’s name here. The French edition prints "acide chlorosulfonique", the name of the preceding entry (016-017-00-1). The EC and CAS numbers in the same row, 232-149-4 and 7789-21-1, are fluorosulphonic acid and are correct. Regulation (EU) 2018/669, OJ L 115, 4.5.2018, p. 72 acide chlorosulfonique |
| Croatian hrvatski | fluorosulfonska kiselina |
| Italian italiano | acido fluorosolfonico |
| Latvian latviešu | fluorsulfonskābe |
| Lithuanian lietuvių | fluorsulfonrūgštis |
| Hungarian magyar | fluorszulfonsav |
| Maltese Malti | aċidu fluworosulfoniku |
| Dutch Nederlands | fluorsulfonzuur |
| Polish polski | kwas fluorosiarkowy(VI) kwas fluorosulfonowy |
| Portuguese português | ácido fluorossulfónico |
| Romanian română | acid fluorosulfonic |
| Slovak slovenčina | kyselina fluorosírová |
| Slovenian slovenščina | fluorožveplova kislina |
| Finnish suomi | fluorisulfonihappo |
| Swedish svenska | fluorsulfonsyra |
One or more lines above are flagged. In those language editions the Regulation as published in the Official Journal prints something that the rest of the same row contradicts — a name belonging to a different entry, or the qualifier of a paired entry. Each flag cites the amending act and the Official Journal page, so the wording can be checked at source. The lines are reproduced as printed, because Art. 18(2) points at Annex VI and not at our reading of it; the note beside each one says what the row’s own EC and CAS numbers identify.
All 23 language editions of Annex VI carry this entry. Irish is the twenty-fourth official EU language and has no line here for a different reason: no consolidated CLP text has ever been published in Irish, so there is no Irish edition of Annex VI to quote a name from. Source: consolidated CLP, CELEX 02008R1272, language editions. © European Union, https://eur-lex.europa.eu — only the electronic Official Journal of the European Union is authentic.
06 · Label elements
Fluorosulfuric acid GHS label elements
Everything CLP Annex VI fixes for Fluorosulfuric acid, laid out the way it appears on a label. The greyed lines are the parts only the supplier can fill in.
Danger
Fluorosulfuric acid
- Harmful if inhaled.
- Causes severe skin burns and eye damage.
- Do not breathe dust/fume/gas/mist/vapours/spray.
- Use only outdoors or in a well-ventilated area.
- Wear protective gloves/protective clothing/eye protection/face protection/hearing protection/…
- IF SWALLOWED:
- IF INHALED:
- Immediately call a POISON CENTER/doctor/…
- Call a POISON CENTER/doctor/… if you feel unwell.
- Do NOT induce vomiting.
Supplier name, address and telephone number· Product identifier·Nominal quantity
Need this as an actual label? Open Fluorosulfuric acid in the GHS label constructor →
07 · Health hazards
Fluorosulfuric acid health hazards and exposure limits
Fluorosulfuric acid hazard summary
Highly corrosive to skin; [Quick CPC] Reacts with water producing hydrofluoric acid and sulfuric acid; [HSDB] Corrosive to skin, eyes, and respiratory tract; Inhalation may cause pulmonary edema; [ICSC] See the Process, Toxic Gas from Spilling Chemical in Water.
Source: Haz-Map, Information on Hazardous Chemicals and Occupational Diseases
08 · Physical and chemical properties
Fluorosulfuric acid properties
Every value is shown with the conditions it was measured under and the source it came from. Where sources disagree, all values are listed rather than one being picked — the difference is usually a different form of the substance, not an error.
Fluorosulfuric acid boiling point
| Property | Value | Conditions | Source |
|---|---|---|---|
| Boiling point | 163 °C (325.4 °F) | at 760 mmHg | HSDB |
| 162.72 °C (324.9 °F) | at 760 mmHg | CAMEO | |
| 163 °C (325.4 °F) | ICSC |
Fluorosulfuric acid melting point
| Property | Value | Conditions | Source |
|---|---|---|---|
| Melting point | -89 °C (-128.2 °F) | HSDB | |
| -87.28 °C (-125.1 °F) | CAMEO |
Fluorosulfuric acid density
| Property | Value | Conditions | Source |
|---|---|---|---|
| Density | 1.7 g/cm³ | ICSC | |
| 1.726 g/cm³ | at 25 °C | HSDB | |
| 1.73 g/cm³ | at 25 °C | CAMEO |
Fluorosulfuric acid solubility
| Property | Value | Conditions | Source |
|---|---|---|---|
| Solubility | SOL IN NITROBENZENE | HSDB | |
| Solubility in water: reaction | ICSC |
Fluorosulfuric acid vapor pressure
| Property | Value | Conditions | Source |
|---|---|---|---|
| Vapor pressure | 2.4752 mmHg | at 25 °C | ICSC |
| 2.5 mmHg | Haz-Map |
Fluorosulfuric acid vapor density
| Property | Value | Conditions | Source |
|---|---|---|---|
| Vapor density | 3.4 (air = 1) | ICSC |
Fluorosulfuric acid corrosivity
| Property | Value | Conditions | Source |
|---|---|---|---|
| Corrosivity | HIGHLY CORROSIVE | HSDB |
Values compiled from PubChem Laboratory Chemical Safety Summary. Temperatures converted to Fahrenheit for reference.
09 · Handling and storage
Fluorosulfuric acid storage and handling
Fluorosulfuric acid safe storage
Dry. Well closed. Separated from food and feedstuffs. See Chemical Dangers.
Source: ILO-WHO International Chemical Safety Cards (ICSCs)
Fluorosulfuric acid incompatible materials
Reacts violently with water to generate hydrogen fluoride & sulfuric acid mists.
Source: Hazardous Substances Data Bank (HSDB)
Fluorosulfuric acid reactivity
FLUOROSULFONIC ACID is very strongly acidic [Merck]. Reacts exothermically with chemical bases (examples: amines, amides, and inorganic hydroxides). These reactions can generate dangerously large amounts of heat in small spaces. Reacts violently with water to generate hydrofluoric acid and sulfuric acid. Reacts with active metals, including such structural metals as aluminum and iron, to release hydrogen, a flammable gas. Can initiate the polymerization of certain alkenes. Reacts with cyanide compounds to release gaseous hydrogen cyanide. Generates flammable and/or toxic gases in contact with dithiocarbamates, isocyanates, mercaptans, nitrides, nitriles, sulfides, and strong reducing agents. Additional gas-generating reactions occur with sulfites, nitrites, thiosulfates (to give H2S and SO3), dithionites (SO2), and carbonates. May catalyze (increase the rate of) chemical reactions.
Source: CAMEO Chemicals
Planning storage for a mix of chemicals? Check Fluorosulfuric acid in the storage compatibility matrix →
10 · Transport
Fluorosulfuric acid UN number and transport classification
Transport classification is a separate system from the GHS classification above. It decides how a package is marked and how a load may be carried; it does not follow from the workplace label, and the workplace label does not follow from it. The entries below are linked by CAS number, never by name.
Fluorosulfuric acid under UN 1777 — shipping name, class and packing group
Europe · ADR 2025, Table A
| Proper shipping name (3.1.2) | Class | Classification code | PG | Labels (column 5) |
|---|---|---|---|---|
| FLUOROSULPHONIC ACID | 8 | C1 | I | |
Source: ADR 2025, Table A of Chapter 3.2 · ECE/TRANS/352 Vol. I (UNECE). Class 8 is “Corrosive substances” (ADR 2.1.1.1).
United States · 49 CFR 172.101 Hazardous Materials Table
| Proper shipping name (column 2) | Class or division | PG | Labels (column 6) |
|---|---|---|---|
| Fluorosulfonic acid | 8 | I | |
Source: 49 CFR 172.101 Hazardous Materials Table · eCFR, revision 2026-08-03. Class 8 is “Corrosive material” (49 CFR 173.2).
11 · Questions
Fluorosulfuric acid — frequently asked questions
What is the CAS number of Fluorosulfuric acid?
The CAS number of Fluorosulfuric acid is 7789-21-1. Its EC number is 232-149-4.
What is the chemical formula of Fluorosulfuric acid?
The molecular formula of Fluorosulfuric acid is FHO3S and its molecular weight is 100.07 g/mol.
What does a Fluorosulfuric acid label have to show?
Under CLP Annex VI the label for Fluorosulfuric acid carries the pictograms Corrosion and Exclamation mark and the signal word is Danger.
Is Fluorosulfuric acid flammable?
CLP Annex VI assigns Fluorosulfuric acid no flammability hazard class. That is not a statement that it cannot burn: the harmonised list only records the hazards that were assessed for it.
Is Fluorosulfuric acid a carcinogen?
CLP Annex VI records no harmonised carcinogenicity classification for Fluorosulfuric acid. Annex VI is a list of agreed classifications, not a list of substances found safe, so this is an absence of a classification rather than a clean bill of health.
What is the boiling point of Fluorosulfuric acid?
The boiling point reported for Fluorosulfuric acid is 163 °C (325.4 °F), at 760 mmHg (HSDB).
What is the melting point of Fluorosulfuric acid?
The melting point reported for Fluorosulfuric acid is -89 °C (-128.2 °F) (HSDB).
Nearby
Substances next to Fluorosulfuric acid
Keep going: substances starting with F, or search the whole database by name, CAS number, pictogram or signal word.