Hydrogen cyanide vapor density

The density of hydrogen cyanide at standard conditions is 1.29 g/l. Calculate the apparent molecular weight of hydrogen cyanide vapor. 

Other than hydrogen cyanide (C07-A001), agent vapors have a density greater than air and tend to collect in low places. However, due to the volatile nature of these materials, there is a minimal extended risk except in an enclosed or confined space. 

Hydrogen cyanide (HCN) is also chemically identified by the synonyms formonitrile, prussic acid and hydrocyanic acid. The physicochemical properties most related to the biological activity and uses of HCN are summarized in Table 1. Notable with HCN is that it is a low boiling point liquid (26.5°C). Related to its low MW (27.04) it has a high vapor pressure (600 mm Hg at 20°C) and low vapor density (0.947 at 31°C), Thus,... 

Problem 1. Determine the vapor density of (i) diethyl ether and (ii) hydrogen cyanide. 

Vapor density of a chemical is directly proportional to its MW. The average MW of air is 29 amu. At 25°C and 1 atmospheric pressure, average air density is 1.19 kg/m. The vapor density of air is referred to as being 1 for the calculation of relative vapor density of other vapors. Any chemical with MW >29 amu would have a vapor density >1 under the same temperature and pressure conditions, according to the Ideal Gas Law. Hence, the vapor is heavier than air and it will tend to stay in or flow to low places. Vapor of chemicals with MW <29 amu have a vapor density of <1. These vapors would tend to migrate to higher places and will be easily diluted by air currents. The vapor densities of aU CWAs and TICs, except for a few chemicals such as hydrogen cyanide, carbon monoxide, diborane, and ammonia, are >1. 

How much heat is needed to vaporize 10.0 mL of liquid hydrogen cyanide, HCN, at 25.0°C The density of the liquid is 0.687 g/mL. Use standard heats of formation, which are given in Appendix C. 

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