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Vapour pressure

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Description of key information

Using a weight of evidence, the vapour pressure of arsenic acid was considered to be 18.45 hPa at 25 °C.

Key value for chemical safety assessment

Vapour pressure:
18.45 hPa
at the temperature of:
25 °C

Additional information

Two secondary bibliographic sources provide vapour pressure (VP) values for arsenic acid. As the primary reference is not traceable, both references are quoted by reliability score of 4 (not assignable). The available values are reported below:

(1) VP = 55 mbar at 50°C and VP = 110 mbar at 65°C

(2) VP = 12.58 hPa at 15°C

The vapour pressure may vary greatly according temperature. For the purpose of the chemical safety assessment, VP values at 25°C are predicted using the equation recommended in EUSES Software version 2.1: VPtempx = VPtemptest x e{ (H0_VP/R) x (1/Temptest – 1/Tempx) } 

Where:

Tempx: temperature of 25°C (equal to 298.15 K)

Temptest: temperature of the measured physico-chemical data (15°C = 288.15 K; 50°C = 323.15 K)

H0_VP: enthalpy of vaporisation (value: 5.104 J.mol-1)

R: Gas constant (value: 8.314 Pa.m3.mol-1.K-1)

Values of extrapolated vapour pressure:

(1) Input 55 mbar at 50°C, Output: 11.5 hPa at 25°C

(2) Input 12.58 hPa at 15°C, Output: 25.4 hPa at 25°C

 

Both values are in the same order of magnitude. Using a weight of evidence, the arithmetic mean of the two values is proposed as key value for the chemical safety assessment: VP25°C = 18.45 hPa