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Physical & Chemical properties

Endpoint summary

Administrative data

Description of key information

Additional information

Pure

Pure formaldehyde is a colourless gas, with a pungent and suffocating odour and has a melting point/freezing point between -92 °C and -118°C and a boiling point of ≥-21 °C and ≤ -19 °C at 1013.25 hPa. The density of pure formaldehyde is 0.815 g/cm³ at -20 °C and the relative density of the gas (air = 1.0) is 1.03 – 1.067. The vapour pressure of pure formaldehyde is ca 5176 - 5186 hPa at 25°C. As a gas, formaldehyde is extremely flammable, because it is ignitable in a mixture of 7 - 73 % by volume in air. The self-ignition temperature is reported to be 395 °C for the pure substance. The log Pow is 0.35. The water solubility is reported to be 550 g/L, such that concentrations of up to 55% can be reached in aqueous solutions. Based on the chemical structure of formaldehyde, no surface activity is predicted. In addition, formaldehyde is non explosive and incapable of reacting exothermically with combustible materials. Based on chemical structure pyrophoric properties and flammability in contact with water are not to be expected.

Aqueous solution

Formaldehyde in aqueous solution (37 to 50 %) is a colorless liquid (at 20 °C and 1013 hPa) with a pungent odour. Cloudiness or opalescence in the formaldehyde solution is caused by polymer precipitation. An aqueous solution of 30.19 % formaldehyde has a melting point/freezing point of -18.8 °C and a boiling point of 98.9 - 99.4 °C at 1013.25 hPa. The density of aqueous formaldehyde solutions is 1.069-1.12 g/cm3 at 20 °C depending on the concentration. The vapour pressure of a 55% aqueous solution is 14 hPa at 20 °C and 92 hPa at 50 °C

The partial pressure of formaldehyde over water is 1.2 hPa and 1.3 hPa at 20 °C for 30 % and 50 % formaldehyde in aqueous solution respectively. The viscosity of aqueous formaldehyde solutions ranges from 2.083 to 2.835 mPa s at 20°C depending on formaldehyde concentrations (30.19 - 40.08% ) and methanol concentrations (0.95 - 11.95%). The pKa for formaldehyde is determined to range from 12.79-13.27 at temperatures ranging from 23-30°C. Aqueous formaldehyde solutions containing ≤10% methanol are non-flammable under Regulation (EC) No. 1272/2008. An aqueous solution of formaldehyd (49,35%) and methanol (1,84%) is, based on DSC, not self-reactive.