How can you determine the concentration of a bleach solution (besides looking on the label)?

Question

I am an anesthetist in Liberia and we process some equipment with bleach for disinfection. The CDC recommends 5.25% solution for this, but the solution we have here (supposedly) is 18%. I can do the math to make a 5.25% soln, but we have no actual docs that say it's 18% and there is some question whether the manufacturer is watering it down. How can I determine approx concentration? I have access to basic lab reagents (of a medical lab), some biological staining dyes (meth blue, indigo carmine, safranin, etc) and fairly accurate measuring equipment, but it's been a long time since I've taken quantitative chem. Any suggestions?

Answer 1

Add excess potassium iodide to a measured volume sample of the bleach.
Then titrate the iodine released against standardised sodium thiosulphate solution, using starch solution as an indicator. Unlike other titrations, starch is added towards the end of the titration process.
This is a standard technique for measuring the concentration of bleach in the UK.

ClO- + 2I- + 2H+ ----> I2 + Cl- + H2O

then

I2 + 2(S2O3)2- ----> (S4O6)2- + 2I-

Answer 2

The solutions are where the graph crosses the x axis. Could be 0, 1, or 2 solutions.

Answer 3

Something as simple as a swimming pool test kit has one test for chlorine concentration (and a test for pH of the pool water), including the necessary chemical indicator reagent(s) and color chart.

I'm sure there must be a swimming pool supply company somewhere in a large city in Liberia. Or, you can order those kits online.

Since you will be working with strong concentrations compared to what the pool concentrations must be, you will have to take a sample of your alledged 18% concentrate and dilute it down accurately so it will be in the range of detection for the pool kit. These kits are sensitive enough to detect a few ppm of Chlorine even in tap water.

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Answer 4

Perform an acid-base titration and include a color based pH (such as phenothaelin)indicator in the solution. Your base would be NaOH (bleach) and a strong acid, HCl.