The average human body contains 6.50 L of blood with a Fe2+concentration of 2.50×10^−5 M . If a person ingests 12.0 mL of 17.0mM NaCN, what percentage of iron(II) in the blood would besequestered by the cyanide ion?
For example, the iron(II) ion, Fe2+Fe2+, can combine with thecyanide ion, CN−CN−, to form the complex [Fe(CN)6]4−[Fe(CN)6]4−according to the equation
Fe2+(aq)+6CN−(aq)⇌[Fe(CN)6]4−(aq)Fe2+(aq)+6CN−(aq)⇌[Fe(CN)6]4−(aq)
where Kf=4.21×10^45
This reaction is what makes cyanide so toxic to human beings andother animals. The cyanide ion binds to the iron that red bloodcells use to carry oxygen around the body, thus interfering withthe blood's ability to deliver oxygen to the tissues. It is thistoxicity that has made the use of cyanide in gold miningcontroversial. Most states now ban the use of cyanide in leachinggold out of low-grade ore.
