Determining the concentration of hypochlorite ion in bleach

hey i was wondering how i can work out the conc. of OCl- ion in bleach to find out what type of commercial bleach is most effective.
i need two method and cant decide what to do except a titration.
i also am not sure what chemicals i should use and how much bleach i would need and how much i should dilute it.

can anyone help or point me in the right direction, specifically for a second method.
thanks

bump, please help

titration?

yeah, why? Would a titration not work or are you suggesting that in which case I have already mentioned it. I'm really not sure what to do at all

Reply 4

Justice †

loopylou74

yeah, why? Would a titration not work or are you suggesting that in which case I have already mentioned it. I'm really not sure what to do at all

sorry didn't actually read that you said that. I was suggesting a titration.

Another method could be by gas collection I suppose. If you found a compound/element which when reacted with the OCl- ions gave off a gas, add an excess to a known volume of OCl- then using the equation you could calc the moles of gas collected and then work out the moles of OCl- and thereby the conc. :biggrin:

That'd work

Reply 5

EierVonSatan

Yeah, do a titration with sodium thiosulfate and Iodine, the amount of OCl- can be determined by finding out how much iodine (I2) it can make from 2I-. The quantity of iodine produced is measured by titrating it with sodium thiosulfate...

Add acidified Iodine to the bleach: 2H+ + OCl- + 2I- ---> Cl- + I2 + H2O

This then forms: I2 + I- ---> I3- (black)

Titration: 2Na2S2O3 + I3- ---> 3I- + S4O6(2-) (colourless solution)

:smile:

Reply 6

loopylou74

thanks guys! I'm fine with the titration I think, it's just the 2nd method. Would a colorimetric determination work? And how would I do that?

Reply 7

EierVonSatan

The only other thing I can think of is ion chromatography, and that's unlikely to be the answer :p:

Reply 8

loopylou74

im still really not sure for this, done the first method fine but not sure about the 2nd.
im going for a colorimetric determination but can anyone give me a bit more help on what i should do

Reply 9

Revd. Mike

If you're going to go for colorimetry, you need to find a reagent that changes colour in the presence of hypochlorite.

Use several samples of known concentration of hypochlorite and plot a standard curve. Then test your samples, and read off the graph :smile:

Reply 10

loopylou74

ok thanks!
i have rhodamine b i think that will work.
im stil not very sure what exactly i have to do though.
i know i need potassium iodide, hydrochloric acid and sodium acetate but im not sure what im doing with it

Reply 11

Revd. Mike

Haven't done this in ages, but roughly: Mix bleach with iodide solution and acidify, the acidification will liberate chlorine which will displace the iodide, forming iodine. You can calculate the amount of iodine liberated by titrating with thiosulfate :smile:

Just need to check the particulars of the procedure like concentrations and amounts and stuff!

Reply 12

loopylou74

right, ok.
i plan to be using 5cm^3 bleach, diluted to 50cm^3.
add potassium iodide solution and hydrochloric acid (any help with volumes?)
shake then add rhodium b solution and sodium acetate (again volumes?)
shake again and dilute then put a sample through a colorimeter.
can anyone help me with volumes and the results?

bump? please help

I'm not too sure about the colorimeter tbh, with regards to the reagents and things.

Reply 15

secondary1

Definitely use a titration - we did this practical in the lab not too long ago.

We used 10cm^3 of bleach, diluted to 250cm^3 in a volumetric flask though.