# Cyanide Titration Revisited



## Gratilla (Dec 22, 2012)

Yesterday I did my first cyanide titration.  This was based on GoldSilverPro's 2009 post cyanide titration, which was significantly clearer than the 11 pages given me from a professional mining services company. I first put together my own notes (shown below) and did a couple of qualitative tests to familiarize myself with what to expect at the end point. Without an indicator, the cloudy white was very difficult to detect, so I was glad that the end point with rodanine was very clear. (I didn't have any KI.)

*Analysis for free Cyanide*: 
(1) Pipette a 10 ml (K or Na) cyanide sample into a 250 ml erlenmeyer flask. *[sample A]*
(2) Add 90 ml of distilled water. *[sample A/10]* 
(3) Add: *[indicator]*
- Nothing, if no indicator is to be used, or 
- 5 ml of 10% KI (potassium iodide) solution, or 
- 5 ml rodanine. 
(4) Titrate with standard 0.1 N AgNO3 (silver nitrate) solution until: *[standard B]* 
- a faint white turbidity persists (no indicator) 
- a faint yellowish turbidity persists (KI indicator) 
- the canary yellow colour changes to salmon pink (rodanine indicator) 
The standard AgNO3 solution is prepared by weighing out exactly 17.00 grams	*[0.1M=0.1N AgNO3]*
of the reagent grade salt and dissolving it in distilled water, *[AgNO3 = 169.88 gm]*
after which it is diluted to exactly 1 liter in a volumetric flask. 
(5) The Sodium Cyanide (NaCN) in gm/liter is equal to: *[NaCN gm/L in A = 0.9825 x B ml]*
0.9825 x ml of 0.1 N AgNO3 used. *[1M NaCN = 49.01 gm 2N = 98.02]*
(If KCN (potassium cyanide) is being used, *[(KCN gm/L in A = 1.306 x B ml)]*
the KCN in gm/liter = 1.306 x ml of AgNO3 used.) *[1M KCN = 65.03 gm 2N = 130.06]*

(Being the sceptic that I am) I cross-checked all the figures and found some differences based on my calculations of molar wts. My figures in blue and GSP's figures from his source in red. Have I made a mistake or is there a good reason for the differences?


----------



## goldsilverpro (Dec 22, 2012)

Gratilla said:


> Yesterday I did my first cyanide titration.  This was based on GoldSilverPro's 2009 post cyanide titration, which was significantly clearer than the 11 pages given me from a professional mining services company. I first put together my own notes (shown below) and did a couple of qualitative tests to familiarize myself with what to expect at the end point. Without an indicator, the cloudy white was very difficult to detect, so I was glad that the end point with rodanine was very clear. (I didn't have any KI.)
> 
> *Analysis for free Cyanide*:
> (1) Pipette a 10 ml (K or Na) cyanide sample into a 250 ml erlenmeyer flask. *[sample A]*
> ...


Technically, you are correct. Practically, it doesn't make much difference. The factors in my source were in avoirdupois ounces (16/pound) per gallon and were given to 3 significant figures. I simply converted them to g/l using the rounded off relationship I have memorized and used for 45 years, 1 av.oz/gal = 7.5 g/l (actually, it's 7.490). My factors, therefore, were not as precise as yours. In reality, since 7.5 only has 2 significant figures, mine were only good to 2 significant figures and I should have used the the factors, 0.98 and 1.3, instead of what I used. The figures I did use varied from the molar calculations by about 0.2% and 0.6%, respectively. That's about 1 part/500 and 1 part/167 errors. The cumulative errors from weighing, pipetting, and titrating (and the question of how dry the AgNO3 was when you weighed it) would be far greater than that and would more than offset the use of more precise factors. At best, using this method is only about 98% accurate. In practice, for measuring cyanide concentration, that accuracy would be fine. For other things, of course, a 2% error would be unacceptable.

On the one hand, your factors are correct and more precise. On the other hand, this method, itself, is reliable but not that precise.

I also noticed that I said 17.00g of AgNO3. I should have said 17.0g. There is some error it that but, here again, it's well within the accuracy of the method.


----------



## Palladium (Dec 22, 2012)

That's what i love about Chris. On one hand he can be the refiner with 5 gallon buckets and waffle griddles and on the other he's one of the most scientific and proficiently mathematically correct people in refining you will meet. Even though i don't quiet understand everything he says, i can still see the genius in it.


----------



## Gratilla (Dec 27, 2012)

Thanks GSP for the explanation.

I've updated my notes in order to be (pedantically) accurate. Also, I've amended make-up of the standard AgNO3 solution (one for NaCN, one for KCN) so that no calculations are necessary after the titration. The concentration of the NaCN/KCN in gm/liter is now equal to the ml of the respective standard AgNO3 used.	

*Analysis for free Cyanide:* 
(1) Pipette a 10 ml (K or Na) cyanide sample into a 250 ml erlenmeyer flask. 
(2) Add 90 ml of distilled water. 
(3) Add: 
a) Nothing, if no indicator is to be used, or 
b) 5 ml of 10% KI (potassium iodide) solution, or 
c) 5 ml rodanine. 
(4) Titrate with a standard AgNO3 (silver nitrate) solution until: 
a) a faint white turbidity persists (no indicator) 
b) a faint yellowish turbidity persists (KI indicator)
c) the canary yellow colour changes to salmon pink (rodanine indicator) 
_The standard AgNO3 solution is prepared by weighing out exactly 17.33 grams of the reagent 
grade salt if NaCN is being used or 13.04 grams of the reagent grade salt if KCN is being used. 
Dissolve in distilled water and dilute to exactly 1 liter in a volumetric flask. _ 
(5) The NaCN/KCN in gm/liter is equal to the ml of the respective standard AgNO3 used.


----------



## 911Met (Mar 31, 2016)

More on this topic at https://www.911metallurgist.com/blog/titration-of-cyanide-solutions-containing-dissolved-zinc and https://www.911metallurgist.com/blog/titration-of-cyanide-solutions-containing-dissolved-copper + https://www.911metallurgist.com/blo...2016/02/cyanide-titration-reference-guide.pdf


----------

