Molar Mass of Hydrofluoric Acid (HF)

Each row shows how much mass one element contributes to the total for HF.

Save a printable summary, revision sheet, practice worksheet, or laboratory reference for Hydrofluoric Acid (HF).

Without looking above, write the atom count for HF, then compute the molar mass. Check your answer against 20.006 g/mol.

Next challenge: how many grams are in 0.250 mol of Hydrofluoric Acid? Multiply 0.250 × 20.006 to get 5.002 g.

Industrial HF emissions are tightly regulated due to acute toxicity to humans, aquatic life, and vegetation; fluoride bioaccumulation and fluorosis in wildlife near uncontrolled emission sources are documented concerns.

Fluoride ion in trace amounts (e.g., from water fluoridation) supports dental health, but concentrated HF exposure is acutely and systemically toxic via calcium sequestration — the therapeutic and toxic faces of fluoride chemistry are governed by a vast concentration difference.

Preparation and production

Industrially, HF is produced by reacting fluorspar (calcium fluoride, CaF₂) with concentrated sulfuric acid: CaF₂ + H₂SO₄ → CaSO₄ + 2 HF, then purifying the gaseous product. This is essentially the only significant production route and should never be attempted outside an industrial or specialized laboratory setting.

Nearly all commercial HF derives from the fluorspar–sulfuric acid reaction at dedicated chemical plants, producing anhydrous HF and aqueous hydrofluoric acid solutions for downstream fluorochemical, glass, metal, and nuclear fuel cycle industries.

Hydrofluoric acid was first isolated in relatively pure form by Carl Wilhelm Scheele in 1771 through reaction of fluorspar with sulfuric acid, though its extreme reactivity and toxicity made handling and further study hazardous for early chemists — several 19th-century researchers were seriously injured or killed while attempting to isolate elemental fluorine from HF-related chemistry before Henri Moissan finally succeeded in 1886.

Carl Wilhelm Scheele, 1771 — first prepared hydrofluoric acid by treating fluorspar (CaF₂) with sulfuric acid, though its hazards significantly complicated further 18th- and 19th-century fluorine chemistry research.

Interesting facts

• HF's molar mass (20.01 g/mol) is the lowest of all the common hydrohalic acids, yet its toxicological hazard profile is arguably the most severe of the group.
• Concentrated HF exposure covering even a modest area of skin (in some documented cases, under 10% of body surface area) has caused fatalities due to systemic calcium depletion and resulting cardiac effects.
• HF's reaction with silica is so specific and reliable that it is used to etch intricate patterns into glass and to strip silicon dioxide layers precisely in semiconductor manufacturing.
• Calcium gluconate gel is the standard first-aid and clinical treatment for HF skin exposure specifically because it supplies calcium ions to bind free fluoride before it can penetrate deeper tissue.

Comparison with similar compounds

HF (20.01 g/mol) is a weak acid (Ka ≈ 6.6 × 10⁻⁴) with uniquely severe systemic toxicity via calcium binding, in sharp contrast to HCl (36.46 g/mol), a fully dissociated strong acid whose hazard is limited to direct, immediately apparent corrosive burns.

⚠️ Store only in HF-compatible containers (polyethylene, PTFE, or specially treated/lined vessels) — never in ordinary glass, which HF actively dissolves. Store away from incompatible materials, with appropriate secondary containment, in a well-ventilated, access-controlled area with calcium gluconate gel readily available nearby for emergency first aid.

⚠️ Extremely hazardous despite being a "weak" acid. Handle only with specialized training, HF-resistant gloves (typically thick neoprene or butyl, not standard nitrile), face shield, and fume hood/local exhaust ventilation. Have calcium gluconate gel and an established emergency response plan immediately available before any work begins. Seek emergency medical care immediately after any skin, eye, or significant inhalation exposure, regardless of apparent severity, because pain and visible damage can be delayed.

Extremely hazardous despite weak-acid classification: causes severe, potentially delayed-onset chemical burns and systemic toxicity via fluoride-induced calcium depletion, which can be fatal even from limited skin contact with concentrated solutions.

• Severe, potentially delayed-onset skin and eye burns that may not be immediately painful
• Systemic toxicity from fluoride binding calcium/magnesium — risk of life-threatening hypocalcemia and cardiac arrhythmia
• Corrosive to metals and glass; reacts with silica-containing materials
• Toxic by inhalation, causing respiratory tract damage and potential pulmonary edema

Classification: GHS: Skin Corr. 1B, Acute Tox. 2 (dermal/inhalation), STOT SE 1

1. 1. Calculate the molar mass of HF.

   Show answer

   1.008 + 19.00 = 20.01 g/mol

2. 2. Why is HF classified as a weak acid even though fluorine is the most electronegative element?

   Show answer

   The H–F bond is unusually strong and short, and extensive hydrogen bonding (including formation of HF₂⁻) in aqueous solution suppresses complete dissociation, giving HF a much smaller Ka (≈ 6.6 × 10⁻⁴) than the fully dissociated strong acids HCl, HBr, and HI.

3. 3. How many grams of SiF₄ form from the complete reaction of 80.04 g of HF with excess SiO₂?

   Hint: Use the 4:1 mole ratio of HF to SiF₄ from the balanced equation.

   Show answer

   80.04 g ÷ 20.01 g/mol = 4.000 mol HF; from SiO₂ + 4 HF → SiF₄ + 2 H₂O, this yields 1.000 mol SiF₄ × 104.08 g/mol ≈ 104.1 g

4. 4. Why can HF cause severe injury even from limited skin contact, unlike many other corrosive acids?

   Show answer

   Fluoride ion penetrates skin readily and binds calcium and magnesium in underlying tissue and blood, causing deep, sometimes delayed-onset damage and systemic hypocalcemia that can trigger cardiac arrhythmia, independent of the acid's pH-based corrosivity alone.

• Hydrochloric AcidHCl
• Sulfuric AcidH₂SO₄

The sections above give the number you need for calculations. Here we look more closely at how Hydrofluoric Acid (HF) behaves chemically—so the molar mass connects to real reactions, properties, and laboratory practice.

Hydrofluoric acid (HF) has a molar mass of just 20.01 g/mol (H 1.008 + F 19.00), among the lightest common acids, yet it is chemically unlike any other hydrohalic acid. Despite fluorine's extreme electronegativity, HF is only a weak acid in dilute aqueous solution (Ka ≈ 6.6 × 10⁻⁴, pKa ≈ 3.17) — far weaker than HCl, HBr, or HI — because the very strong H–F bond and extensive hydrogen bonding in solution resist full dissociation, and the resulting bifluoride ion (HF₂⁻) chemistry further complicates its equilibrium behavior compared to simple strong-acid models.

What makes HF exceptionally dangerous is not its acid strength but its unique chemistry with calcium and magnesium: the small, highly mobile fluoride ion penetrates skin and tissue readily (unlike most acids, which cause immediate, visible surface burns) and binds tightly to Ca²⁺ and Mg²⁺, forming insoluble calcium fluoride and depleting these essential ions from cells and blood. This can cause severe, delayed-onset chemical burns, systemic hypocalcemia, cardiac arrhythmia, and death from even modest skin contact area, especially with concentrated solutions — a toxicological profile that has nothing to do with pH and everything to do with fluoride's specific ion chemistry. Burns may not be immediately painful, delaying treatment and worsening outcomes.

Industrially, HF's ability to react with silica and silicates — a reaction essentially no other acid can perform — makes it indispensable for glass etching, frosting, and cleaning; for dissolving mineral samples in analytical geochemistry; and for producing fluorocarbons, aluminum fluoride, and enriched uranium hexafluoride in the nuclear fuel cycle. This same silica-dissolving property means HF must never be stored in ordinary glass containers, unlike virtually every other common acid.

HF is a simple diatomic molecule with a highly polar covalent bond (the most polar single bond among common hydrogen halides) due to fluorine's extreme electronegativity. In the gas phase and in concentrated solution, HF molecules extensively hydrogen-bond, even forming chain and ring oligomers (HF)ₙ; in dilute aqueous solution, incomplete dissociation and formation of the bifluoride ion HF₂⁻ (via HF + F⁻ ⇌ HF₂⁻) make its acid-base behavior more complex than the simple monoprotic picture the formula suggests.

HF is the only common acid that reacts with and dissolves silicon dioxide and silicate glass: SiO₂ + 4 HF → SiF₄ + 2 H₂O (or, with excess HF, forming soluble hexafluorosilicic acid, H₂SiF₆). It reacts vigorously with many metals and metal oxides to form fluoride salts, and its fluoride ion forms extremely stable complexes with highly charged cations (Al³⁺, Fe³⁺) and with Ca²⁺/Mg²⁺, which underlies both useful analytical applications and its severe toxicology.

Recalculate any formula with the molar mass calculator, compare atoms on the periodic table, or browse more compounds in the acid library.

• NIOSH Pocket Guide to Chemical Hazards: HF exposure limits and toxicological data
• NIST Chemistry WebBook: HF thermophysical properties
• PubChem CID 14917: Hydrogen fluoride identifiers and safety data