Passage Cyanide (CN − ) is a powerful, rapid toxin that binds to the cellular respiratory enzyme cytochrome c oxidase. The resulting enzyme-cyanide complex blocks the transfer of electrons to oxygen in the last step of the electron transport chain. This results in cytotoxic anoxia, causing asphyxiation at the cellular level.Exposure to cyanide can occur from dietary sources, medical treatments, industrial applications, smoke inhalation (structural fires), and intentional use (suicide). While dietary exposure from moderate consumption of naturally occurring plant compounds such as cyanogenic glycosides rarely results in acute adverse effects in humans, chronic effects have been observed from prolonged diets with significant levels of these compounds. In the developed world, risk of significant cyanide exposure is most likely to result from smoke inhalation during building fires or from industrial/occupational exposures.The impact of a given exposure depends on the amount (dose, duration), the chemical composition of the cyanide compound (HCN, NaCN, KCN), and the route of exposure (inhalation, absorption, ingestion). The ionic salts (NaCN, KCN) and free acid (HCN) forms of cyanide each have different acid-base properties that interact differently under the physiological conditions associated with each route of exposure.To better understand the toxicity of different forms of cyanide, animal models have been studied for comparison to known human exposure case studies. Table 1 presents a summary of selected animal toxicity studies that examine exposure via ingestion. The table provides the lethal dose to 50% of the population (LD 50 ) in milligrams of cyanide per kilogram of body weight (mg/kg).Table 1 Compilation of LD 50 Cyanide Values in Various Animal Species Based on animal models, one treatment developed for cyanide poisoning involves assisting the rhodanese enzyme in metabolizing CN − to SCN − via an intravenous solution of NaNO 2 and Na 2 S 2 O 3 . The Na 2 S 2 O 3 assists in the formation of a reactive S-SH (persulfide) bond in the enzyme on cysteine-247 (Reaction 1), which then reacts with the cyanide ion to form thiocyanate (Reaction 2). Adapted from: Hall AH, Isom GE, Rockwood GA. Toxicology of Cyanides and Cyanogens, Experimental, Applied and Clinical Aspects. John Wiley & Sons; 2015: 1-20; and Egekeze JO, Oehme FW. Cyanides and their toxicity: A literature review. Vet Q. 1980; 2(2): 104-114. -The base dissociation constant K_b for the hydrolysis of an alkali metal cyanide salt is given by the relation: where [OH^-],[HCN], and [CN^-] are the molar concentrations of the relevant chemical species. What is the pH of an aqueous solution that is 0.001 M in KCN salt? (Note: K_a ≈ 1 × 10⁻⁹ for HCN, and pH ≠ pK_a in this solution.)

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11ecba2d_11c9_43d6_a3bf_b7e7f4153456_MD0008_00 KCN is a water-soluble potassium salt of the conjugate base of HCN. In water, the KCN dissociates fully into K⁺ and CN⁻ ions. Both KCN and HCN have the CN⁻ ion, and the base dissociation constant K_b for CN⁻ is the same regardless of whether it comes from KCN or HCN. Moreover, the K_b of CN⁻ is related to the acid dissociation constant K_a of HCN by the self-ionization constant K_w of water as follows: K_aK_b = K_w Therefore, dividing K_w by K_a yields K_b: K_b = K_w /K_a K_b = (1.0 x 10⁻¹⁴ M²)/(1.0 × 10⁻⁹ M) K_b = 1.0 × 10⁻⁵ M Evaluation of the [OH⁻] using the K_b yields [OH⁻] = 1 × 10⁻⁴ M. From this value, the pOH can then be determined: pOH = −log[OH⁻] pOH = −log(1.0 × 10⁻⁴) pOH = 4 Using pOH then enables the calculation of pH by the relationship between pOH and pK_w: pH + pOH = 14 pH = 14 − pOH = 14 − 4 pH = 10 Therefore, an aqueous solution of KCN is a basic solution. (Choice A) pH 6 is the pH of a 0.001 M HCN solution (a weak acid). It is not the pH for a solution of 0.001 M KCN, a salt of the conjugate base of HCN. (Choice B) When the pH is 7, a solution is neutral. The CN⁻ ion of KCN acts as a base (proton acceptor), which makes an aqueous KCN solution basic (pH > 7), not neutral. (Choice C) The pK_a is 9, but this is not the same as the pH of the solution. Although the small value of K_a does indicate that HCN is a weak acid, the pH depends on the concentration of protons present in solution. Educational objective: A water-soluble salt formed from the conjugate base of a weak acid dissociates fully in an aqueous solution. Because the salt contains the conjugate base of a weak acid, the resulting solution often exhibits a basic pH with a base dissociation constant K_b that correlates to the corresponding weak acid.

Passage Cyanide (CN−) Is a Powerful, Rapid Toxin That Binds to to the Cellular

Passage Cyanide (CN⁻) Is a Powerful, Rapid Toxin That Binds to to the Cellular