Iodometric Titration of Copper

This video demonstrates the key steps in an iodometric titration of copper. Starting from a solid sample the copper is dissolved in nitric acid and prepared for titration. The titration itself is indirect, the potassium iodide undergoes a redox reaction with the copper ions. The product of this reaction is then titrated with thiosulfate using a starch indicator.

Category:

Education

Tags:

• Analytical chemistry
• titration
• iodometry
• copper

[anibaljuanleandro]

Could you tell me if this pocess can be used to determinate copper in a mineral? and can tell me which is the factor of the thiosulphate to determinate copper?

[crharrison]

@anibaljuanleandro This titration process could be used to detect copper in a mineral sample, however, I am unsure as to wether or not other metals could undergo a reduction similar to what copper does in this reaction. If that were the case, the potential for error could be high. The thiosulfate is used as a titrant used to quantify the amount of triiodide which is formed in proportion to the amount of copper in the sample.

[ryoshi100]

I know you need an acid to titrate this guy, but why HF??

Not something I could exactly do with my homeschool group haha

[crharrison]

@ryoshi100 To be honest, I'm unsure why ammonium bifluoride is used in this process, I was not the one who designed the experiment. It may have been chosen for some consideration of the redox chemistry but without further research I couldn't say. As for the dangers of using it, frankly, I wouldn't be too concerned. The quantities are small and using a solid makes it somewhat safer. I've seen more potential for injury with the dissolution of the copper.

[akibble99]

MILK!

[LiamDaLemon]

@crharrison TY :)

[crharrison]

@LiamDaLemon I think I understand what you mean now. I am unclear on the specific mechanism of the formation of cuprous iodide, what you have found may very well be correct.

When the KI is added (3:38) sinks to the bottom of the flask when added and proceeds to react with the copper in that area, when the solution is stirred the I- is capable of reacting with the remaining copper in solution. Though it looks like the yellow disappeared it had just settled somewhat at the bottom of the flask.

[LiamDaLemon]

@crharrison Oh no... sorry I don't think I explained myself very clearly - I understood the titration itself, it's the bit before with the cuprous iodide that I'm unsure about. When I look it up I find sources tell me that CuI2 is produced, which then immediately decomposes to form CuI and I2. I thought this was what happened at 3.38.

Then at 3.50 when you were shaking the conical flask you shifted the equilibrium, getting CuI2 again.

(this is what I thought... and now I'm confused :P )

[crharrison]

@LiamDaLemon Note quite, the reaction between Cu and KI results in Cu2I2 (cuprous iodide) and I2 (iodine). It is the I2 that is then titrated by the thiosulfate to yield iodide once again. The reaction is quantitative when an excess of KI is used in the reaction, yielding one iodine molecule for every two moles of copper in solution. The relevant reactions are below:

2Cu2+ + 4KI ⇌ Cu2I2(s) + I2 + 4K+

I2 + 2S2O32- ⇌ 2I- + S4O62-

I hope this clears things up for you.

[LiamDaLemon]

What's going on with the KI???

Am I right in thinking that the reactions produces copper(II)iodide which then decomposes into iodine and copper(I) iodide? Then when you mixed it around you simply shifted the equilibrium back again?

vot is goin on?