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Physical & Chemical properties

Appearance / physical state / colour

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Description of key information

Pure formaldehyde is a colourless gas, with a pungent and suffocating odour.
Formaldehyde in aqueous solution (37 to 50 %) is a colourless liquid (at 20 °C and 1013 hPa) with a pungent odour. Cloudiness or opalescence in the formaldehyde solution is caused by polymer precipitation.

Key value for chemical safety assessment

Additional information

Formaldehyde pure substance

Twelve databases were identified regarding the appearance, physical state and colour of pure formaldehyde. 

Based on the Merck index( 2013), The HSDB database (2015) and the EPA publication (2008) pure formaldehyde is a colourless gas, with a pungent and suffocating odour.

In agreement with the above, the GESTIS database (2015), Hawley's dictionary (2002), the RömppChemie (2015), Ullmanns Encyclopedia (2012), Knovel (2012) and INCHEM (1991) report formaldehyde as a colourless gas (at 20 °C and 1013 hPa), with a pungent odour.

The CRC handbook as well as Verschueren (2001)only mention that formaldehyde is a colourless gas.

According to SYKE( 2015) pure formaldehyde is a colourless gas at (20 °C and 1013 hPa) with a characteristic, hay, straw like, pungent odour.

Formaldehyde aqueous solution

Six databases were identified regarding the appearance, physical state and colour of formaldehyde in aqueous solutions. 

Based on the handbook from Walker (1967), formaldehyde in aqueous solution (37 to 50 %) is a colourless liquid (at 20 °C and 1013 hPa) with a pungent odour. Cloudiness or opalescence in the formaldehyde solution is caused by polymer precipitation.

This information was confirmed by the other identified handbooks and databases. The available information is shortly summarized below.

Merck 2013: A ca. 37% (wt) of formaldehyde solution in water. Usually with 10-15 % methanol is a c olourless liquid (at 20 °C and 1013 hPa) with a pungent odour. On standing, especially in the cold, may become cloudy.

Gestis 2015: A colourless liquid (at 20 °C and 1013 hPa) with a pungent odour

EPA: 2008: A 37% formaldehyde by weight aqueous solution in water, usually with 0.5% to 15% methyl alcohol added to prevent polymerization to a solid crystalline form is a colourless liquid (at 20 °C and 1013 hPa) with a pungent odour.

RömppChemie 2015: : A ca. 37% (wt) of formaldehyde solution in water. Usually with 10-15 % methanol is a colourless liquid (at 20 °C and 1013 hPa) with a pungent odour.