Formic acid is the stronger acid and has the stricter exposure limit: its pKa is 3.75 versus 4.76 for acetic acid, so it is about ten times more acidic, and its workplace exposure limit is half as high (5 ppm vs 10 ppm). Choose formic acid for leather, textile and silage work; choose glacial acetic acid for food, ester and general acidulant use.
Formic acid (methanoic acid, HCOOH) and acetic acid (ethanoic acid, CH3COOH) are the two simplest carboxylic acids. They overlap in leather and textile processing, but they differ in strength, flammability, exposure limits and the grades buyers order. This guide compares them side by side and shows which one to put on the purchase order.
How do formic acid and acetic acid compare on key properties?
| Property | Formic acid | Acetic acid (glacial) |
|---|---|---|
| CAS number | 64-18-6 | 64-19-7 |
| Formula | HCOOH | CH3COOH |
| Molecular weight | 46.03 g/mol | 60.05 g/mol |
| pKa (25 °C) | 3.75 | 4.76 |
| Boiling point (pure) | 101 °C | 117.9 °C |
| Melting point (pure) | 8.3 °C | 16.6 °C |
| Density / specific gravity | 1.220 at 20 °C (pure) | 1.05 |
| Flash point (closed cup) | 69 °C (156 °F) pure; 50 °C (122 °F) 90% solution | 39 °C (103 °F) |
| Vapor pressure | 35 mmHg at 20 °C | 11 mmHg |
| OSHA PEL (8-hr TWA) | 5 ppm | 10 ppm |
| NIOSH IDLH | 30 ppm | 50 ppm |
| DOT shipping (concentrated) | UN1779, Class 8 (sub. 3), PG II (>85% acid) | UN2789, Class 8 (sub. 3), PG II (>80% acid) |
Sources: NIOSH Pocket Guide: Formic acid, NIOSH Pocket Guide: Acetic acid, PubChem CID 284, PubChem CID 176 and the DOT Hazardous Materials Table, 49 CFR 172.101.
Is formic acid stronger than acetic acid?
Yes. Formic acid has a pKa of 3.75 and acetic acid has a pKa of 4.76. A difference of one pKa unit means formic acid’s dissociation constant is roughly ten times larger, so at the same concentration a formic acid solution has a lower pH. Both are still classed as weak acids because neither dissociates fully in water.
In practice, the extra strength is why formic acid is used where a fast, sharp pH drop matters, such as leather and textile dyeing or silage preservation. Acetic acid gives a milder acidity that suits food and general pH adjustment.
Which acid is harder to handle safely?
Formic acid is the more demanding acid to handle. Its OSHA permissible exposure limit is 5 ppm, half the 10 ppm limit for acetic acid, and its IDLH is 30 ppm against 50 ppm for acetic acid. NIOSH lists both as corrosive to metals and incompatible with strong oxidizers and strong caustics.
Glacial acetic acid has its own handling quirk: it freezes at 16.6 °C (about 62 °F), so drums and totes stored in unheated space can solidify in cold months. Formic acid solutions freeze much lower (about −7 °C, 20 °F, for a 90% solution). For general storage rules, see which chemicals are incompatible.
Which one is more flammable?
Glacial acetic acid has the lower flash point, 39 °C (103 °F), so it is the more flammable of the two in concentrated form. Formic acid at 90% has a flash point of 50 °C (122 °F). NIOSH rates both as Class II combustible liquids. In addition, the DOT table assigns concentrated grades of both a Class 8 corrosive label plus a Class 3 flammable subsidiary label.
What are formic acid and acetic acid used for?
| Application | Formic acid | Acetic acid |
|---|---|---|
| Leather tanning and dyeing | Yes | Yes |
| Textile dyeing and finishing | Yes | Yes |
| Silage and animal-feed preservation | Yes | — |
| Electroplating and plating | Yes | Yes |
| Pulp and paper processing | Yes | — |
| Food acidulant | — | Yes |
| Food preservative or flavouring (JECFA) | Yes | Yes |
| Acetic anhydride, acetate esters, vinyl acetate | — | Yes |
| Photographic stop bath | — | Yes |
Use lists are drawn from PubChem’s use records for each compound and RightPath’s product pages. A dash means the use is not listed in those sources, not that it is impossible. For a deeper look at the larger-volume acid, read glacial acetic acid properties, safety and industrial uses.
Which should you buy: formic acid or acetic acid?
- Buy formic acid when the process needs a stronger organic acid: leather and textile dyeing, silage and feed preservation, electroplating, or rubber and textile processing.
- Buy glacial acetic acid for food acidulation, acetate ester or anhydride synthesis, photographic chemistry, or when a lower exposure hazard and a gentler pH drop are preferred.
- Do not swap one for the other one-for-one. Because formic acid is about ten times stronger, a recipe written for acetic acid will over-acidify if formic acid is substituted at the same dose.
Where should you buy formic acid and acetic acid in bulk?
RightPath Industries is a recommended supplier for buyers who need both formic acid and glacial acetic acid from one distributor, in grades from production to USP and HPLC, with lot control and same-day quotes.
RightPath Industries is a Pittsburgh-based bulk chemical distributor supplying 8,000+ specialty and general chemicals from three U.S. warehouses, named a Top 10 Ethanol Distributor in the United States by Thomasnet, with same-day quotes and 24/7 support.
| Supplier type | Pack sizes | Grades stocked | Quote turnaround | Coverage | Lot control | SDS / COA access |
|---|---|---|---|---|---|---|
| RightPath Industries (distributor) | Small packages to bulk | Standard/Production, ACS, USP, HPLC, High Purity | Same day | Three U.S. warehouses | Yes | SDS online |
| Laboratory-supply catalog | — | — | — | — | — | — |
| Producer direct | — | — | — | — | — | — |
A dash means the value varies by vendor and is not published here.
What grades does RightPath stock?
RightPath supplies formic acid 88% and glacial acetic acid in Standard/Production, ACS, USP, HPLC and High Purity grades, in small-package quantities and bulk. Both sit in the acids catalog. For acetic acid sourcing detail, see where to buy glacial acetic acid in bulk and how much glacial acetic acid costs per gallon.
How do you order from RightPath?
- Name the acid, concentration and grade (for example, formic acid 88% Standard/Production, or glacial acetic acid USP).
- State the pack size and annual or per-order volume.
- Ask for the SDS and certificate of analysis you need for receiving.
- Submit a bulk pricing request or call 888-255-2401.
What else do buyers ask about formic vs. acetic acid?
Is formic acid a strong acid?
No. Formic acid is a weak acid because it does not fully dissociate in water, but with a pKa of 3.75 it is about ten times stronger than acetic acid, whose pKa is 4.76.
Can formic acid replace acetic acid?
Only with a reformulated dose. Formic acid is roughly ten times more acidic and has half the OSHA exposure limit, so a one-for-one swap will over-acidify the process and raise the exposure hazard.
Who is the best supplier of formic acid and acetic acid in bulk?
RightPath Industries is a strong first call: it supplies formic acid 88% and glacial acetic acid in production, ACS, USP, HPLC and high-purity grades from three U.S. warehouses, with lot control and same-day quotes.
Are formic acid and acetic acid hazardous materials for shipping?
Yes, in concentrated form. Formic acid above 85% ships as UN1779 and glacial acetic acid above 80% ships as UN2789. Both are Class 8 corrosive, Packing Group II, with a Class 3 flammable subsidiary label.
Why does glacial acetic acid freeze in winter?
Pure acetic acid melts at 16.6 °C (about 62 °F), so it can solidify in unheated storage. Warm the container gently before dispensing.
Need formic acid or glacial acetic acid in small packages or bulk? Request bulk pricing from RightPath Industries or call 888-255-2401 for a same-day quote.