Chemical Identity and Composition

3.2.2Physical properties

Table 3. . Physical properties of sodium cyanide (NaCN)

Property		Value	Reference
Molecular weight		49.01	ATSDR (2006)
Melting point		563.7°C	ATSDR (2006)
Boiling point		1496°C	ATSDR (2006)
Specific gravity, solid		1.595 at 20°C 1.6 at 25°C	Gerhartz (1985) DuPont (1996)
Specific gravity, liquid		1.16 to 1.19 at 25°C (~30% solution in water - commercial product)	CSBP (2003a)
Apparent bulk density (solid products)	0.75-0.96 kg/m3		DuPont (1996), CSBP (2003b)
Vapour pressure (mm Hg)		0.76 at 800°C 1 at 817°C 10 at 983°C 89.8 at 1200°C 314 at 1360°C	Clayton and Clayton (1994), DuPont (1996), ATSDR (2006)
Heat of vaporisation		3041 J/g	Kirk-Othmer (1991)
Henry’s Law constant (KH)		No data for NaCN; For HCN (pertinent to NaCN in solution): 5.1x10-2 atm-m3/mol at 25°C and saturation pressure 1.32x10-2 atm-m3/mol at 25°C and infinite dilution, increasing with ionic strength and temperature	ATSDR (2006) ATSDR (2006) Lye (2002), Staunton (pers. comm. 2005)
Partition co-efficient (Log Pow)		0.44	ATSDR (2006)
Sorption co-efficient (Log Koc)		No data	ATSDR (2006)

Flash point	No data for NaCN; For HCN: -17.8°C (closed cup)	ATSDR (2006)
Autoignition temperature	No data for NaCN; For HCN: 538°C	ATSDR (2006)
Solubility in water	Freely soluble in water: 480 g/L at 10°C 580 g/L at 20°C HCN is miscible with water	ATSDR (2006) IPCS (2003)
Solubility in other solvents	Slightly soluble in ethanol and formamide, 1.235 g/100 g in 100% ethanol at 25°C Dissolves in methanol 60.5 g/L (saturated solution at 15°C) Dissolves in liquid ammonia 37 g/L NH3 at –33°C	ATSDR (1997), Gerhartz (1985) DuPont (1996) DuPont (1996)
Flammability limits	Cyanide salts are not combustible, but HCN, which may be produced by solid cyanides on contact with heat or water, is a flammable gas. Dry chemical fire extinguishers or sand are therefore stipulated for fire control and carbon dioxide must not be used (see Section 23.3.1).	NOHSC (1993)
Explosive limits	Cyanide salts are not explosive under normal conditions, but may explode if melted with nitrite or chlorate at about 232°C. Cyanide reacts violently with magnesium, nitrites, nitrates, and nitric acid. HCN gas is potentially explosive when concentrated. There is also a risk of explosion when water comes into contact with molten cyanide.	NOHSC (1993) NSC (2002)
Odour threshold	NaCN is odourless when dry, emits slight odour of HCN in damp air, HCN odour threshold is 0.8-4.4 ppm v/v in air, 0.17 mg/L in water.	ATSDR (2006)

3.2.3Chemical properties

Cyanide referred to in this report includes all cyanide compounds determined to have the cyanide ion (CN^-), by the methods described in APHA (1998). In CN, the carbon is triple bonded to the nitrogen (Mills, 2001). The cyanide compounds in which cyanide can be obtained as CN^- are classified as simple and complex cyanides (APHA, 1998; Table 3.).

Table 3. Selected common metal-cyanide complexes and compounds

Term and Degree of Complexity	Examples of Species or Compound
Free cyanide	CN-, HCN
Simple Compounds a) Readily soluble compounds	KCN (solid), NaCN.2H2O (solid), Ca(CN)2 (solid)
b) Relatively insoluble compounds	CuCN (solid), Zn(CN)2 (solid), Ni(CN)2 (solid)
Weak complexes	Cd(CN)42-, Zn(CN)42-
Moderately strong complexes	Ni(CN) 42-, Cu(CN)2-, Cu(CN)32-, Cu(CN)43-, Ag(CN)2-
Strong complexes	Fe(CN)64-, Fe(CN)63-, Au(CN)2-, Co(CN)64-
Other cyanide-related species Thiocyanate, cyanate Cyanogen	SCN-, OCN- (CN)2
Principal source: Scott and Ingles (1987).

Sodium cyanide is one of a number of simple cyanide compounds or salts. Simple cyanides are represented by the formula A(CN)_x, where A is an alkali metal (sodium, potassium, with ammonium behaving similarly) or other metal, and x the valence of A, is the number of CN groups (APHA, 1998).

Complex cyanides have a variety of formulae, but the alkali-metallic cyanides normally can be represented by A_yM(CN)_x, where A represents the alkali metal y times, M is a metal (ferrous and ferric iron, cadmium, copper, nickel, silver, zinc and others), and x the number of CN groups. X is the valence of A taken y times plus that of the metal.

HCN molecules will polymerise to form extremely inert HCN polymer if solutions are made without alkali addition. In dilute solutions, HCN polymer will generate colours ranging from pale yellow to dark reddish brown. In stronger alkaline solutions, a dark brown precipitate resembling iron rust can form. High pH solutions (e.g. pH 12) will limit the potential for HCN formation and consequently the potential for HCN polymerisation (DuPont, 1996).

HCN is a weak acid with an ionisation constant (pKa) of 9.31 - 9.35 at 20°C (Section 23.3.1) and 8.99 at 35°C (Izatt et al., 1962).

3.2.4Conversion factors

Table 3.. Conversion factors

Hydrogen Cyanide (HCN)	Conversion
In Air: HCN mg/m3 to ppm in air at 20°C HCN mg/m3 to ppm in air at 25°C	1 mg/m3 = 0.890 ppm (v/v)* 1 mg/m3 = 0.90 ppm (v/v)**

* ATSDR (2006); ** based on equation: C_ppm = 1 mg/m³ x 24.45/gram molecular weight of 27.03, where 24.45 is the molar volume of air in litres at normal temperature and pressure (25°C and 760 torr).

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