# ClO2 chlorine dioxide how to know if it is still active or not ? by color ? by smell ? by reaction?

my wife have ClO2 tablet form. she dilutes it to be put inside mister. each time she make the dilution:

package instruction: 1 tablet to 1 liter water => 100ppm ClO2 *we name this 100ppm as "original soln"

she takes 100ml from the "Original soln" to make 1 liter of solution to do household cleaning. may i know how much ppm is the final solution that she used to do cleaning ? i think should be 10ppm solution , right ? 10% mix.

thx

## 1 Answer

If you start with $$\pu{100 mL}$$ stock solution at $$\pu{100 ppm}$$ concentration, and dilute this by a factor of 10 to yield $$\pu{1 L}$$, then you are correct, the later one has a concentration of $$\pu{10 ppm}$$. Keep both in a cool place.

As to check if the solution still is active, or not, and both stock and diluted solution at the expected concentration (which will decrease already if the solution is exposed to hot summer temperatures), you may use test strips you immerse dip into the solution, dry at room temperature, and compare against a scale. An example were the following

(source)

Depending on the manufacturer, the scale of concentration to test may vary.

• someone told me as long as the liquid still have greenish color, that means it is still active.. is that so ? ti saw a bottle of 10ppm ClO2 liquid under wash basin cupboard. it is still greenish color with little smell, no idea how long has she leave it there in room temperature. if soak my hand in 10ppm liquid, will i feel any thing ? i am in germany, i can't find this ClO2 test strip at all. are free chlorine test strip can be use? such as these sensafe.com/shop-all/… – andrew_ysk Aug 16 '20 at 18:29
• «If it is still greenish in color», this depends too much on the light you use & the thickness of the solution you look across from wall to wall; thus I don't trust this approach. «Free chlorine» refers to Cl2 / chlorine gas, but this is not ClO2. Re test stripes, I found lovibond.com/en/PM/Water-Testing/Products/Reagents-Standards/…, chlordioxidteststreifen.de, or on amazon.de with keyword «chlordioxid teststreifen». Some of the pharmacies still prepare medicine on demand, thus they might help you to get them, too. – Buttonwood Aug 16 '20 at 20:33
• Note ChemSE however has a policy to refrain from the provision of medical advice, already because most of us users here are not physicians. – Buttonwood Aug 16 '20 at 20:36
• your advice is good enough. even so, stackexchange policy is for caution. and some of ppl who are here are not stupid as well. lol . thanks for your advice , appreciate it. – andrew_ysk Aug 21 '20 at 5:06