Question

Thiocyanate is so much less harmful than cyanide that adding thiosulfate is actually part of the treatment for cyanide poisoning. How can your test distinguish between the presence of thiocyanate and the presence of the lethal cyanide?

A. To distinguish the presence of cyanide with thiocyanate, a sulfate test can be done. If a precipitate forms, there is sulfur in the solution, and thiocyanate is present.

B. Thiocyanate can be dissociated under weak acidic conditions, then oxidized into carbonate, sulfate, and ammonia. A qualitative analysis test will detect any carbonate, sulfate, or ammonia. If the sulfate is present, you can conclude that there is thiocyanate but not cyanide.

C. Thiocyanate is less intense than cyanide, so when performing the test, if the result is stronger that means cyanide is present. If the result is weaker that means only thiocyanate is present.

D. Upon addition of acid and iron(III) nitrate, thiocyanate will form a dark red solution while the cyanide will form a blue solution.

E. The sample will need to be tested twice: once with thiocyanate and once without it. If a red color appears both times, thiocyanate is present, but not cyanide.

Answer 1

E. The cyanide ion reacts with sulphar to form SCN^-.

The sample will need to be tested twice: once with thiocyanate and once without it. If a red color appears both times, thiocyanate is present, but not cyanide.

First time sample is treated with ferric ions after adding thiosulphate OR S₂^2- -- Red color appear, this is due to formation of Ferric thiocyanate

CN^-+S₂^2--------SCN^- + S^2-

Fe³⁺ + SCN^- ------Fe(SCN)²⁺ RED COLOR SOLUTION---cyanide present

Second time sample is treated with ferric ions without adding thiosulphate OR S₂^2- --

if cyanide no red color

If Red color appear, this is due to formation of Ferric thiocyanate

CN^-+ Fe³⁺------- no red color IF CYANIDE PRESENT

Fe³⁺ + SCN^- ------Fe(SCN)²⁺ RED COLOR SOLUTION--- MEANS THIOCYANATE present