If I measure total chlorine using some of the commonly available kits, what is actually measured? Does it include chlorides? Or which chlorine
compounds are accounted for by the test?JJay - 5-9-2017 at 01:20
Total chlorine includes all chlorine, including chlorides and chlorinated compounds. e.liska - 5-9-2017 at 01:26
[Edited on 5-9-2017 by JJay]SWIM - 5-9-2017 at 02:16
If by 'commonly available' you mean the total chlorine testing kits for pools, the manufacturers describe these kits as testing for both free chlorine
and chloramines.
The chloramines are described as 'combined chlorine' in the context of swimming pool chlorine levels.
These tests are used, according to their manufacturers, because chloramine is smellier, more irritating, and less effective in sanitizing the pool;
making it undesirable.
These chlorine and chloramine levels in pools (1 to 3 PPM) are several times higher than the chlorine levels used in tap water.
However they are much lower than the chloride levels in most tap water, which can be 20 times higher and vary widely from place to place depending on
the water source.
This makes it unlikely that these test kits respond to chloride, as otherwise the 'noise' from the variable water quality would be much higher than
the 'signal' (the 'total chlorine').woelen - 5-9-2017 at 03:20
The so-called total chlorine can be described easily. It is the total amount of elemental chlorine, formed when an excess of hydrochloric acid is
added to the compound to be tested. It is expressed in % of mass of the compound to be tested.
E.g. if you have bleach with a so-called total chlorine contents of 4%, then this does not mean that it contains 4% by weight of sodium chlorite, but
it means that by adding excess hydrochloric acid to 100 grams of this solution (which is a little bit less than 100 ml) you get 4 grams of elemental
chlorine (Cl2).
The total chlorine contents of some compounds can even be larger than 100%. If you take e.g. solid LiOCl (lithium hypochlorite, sometimes used as a
pool chlorinator), then the total chlorine contents is larger than 100%. Just try the computation, using this equation:
LiOCl + 2HCl --> LiCl + H2O + Cl2.
One mole of LiOCl produces one mole of Cl2 and one mole of Cl2 has more mass than one mole of LiOCl.e.liska - 5-9-2017 at 03:20
Is described as testing for chlorine and chloramine at low concentrations by their ability to oxidize The Iodide ion to free Iodine.
I don't think traces chloroform (trichloromethane) are going to interfere with that.
According to the link oxidizers are the other agents which commonly effect the test.
Are you concerned about your local water quality?
I hate to think there might be another Woburn type situation out there,.
feacetech - 6-9-2017 at 16:07
for water treatment I use to measure Free Avliable Cholrine (FAC or FAH) and cholride (silver nitrate and dichromate indicator) among other spot
tests, these were simple on the spot tests colourmetric and titrimetric
FAC is good becase it measures halogens in the more active form for disinfection.
this was for cooling water, FAC of 0.5-1.5 was desired and i used the chloride figure with others to calculate a Larson-Skold index
this may be helpful to explain some of the different tests for chlorine and what they measure
I especially need to be sure there are no chloramines, which are very toxic for my purposes.feacetech - 7-9-2017 at 19:52
so TAC - FAC would give you an estimate
however Chlorine is very reactive and in water and forms every possiable nasty you could think of if there loading in the water
byproducts cholrination
CLO2 is meant to be better and produce little to no byporducts of chlorinationAJKOER - 10-9-2017 at 05:29
Here is a household chemical path to hopefully assess the available hypochlorite/HOCl content. Note, water quality including, for example, nitrate,
dissolved organic matter and transition metals (especially iron from ferrous bicarbonate), all can consume NaOCl/HOCl, so calibrating for the target
water source, to establish appropriate free chlorine level, is advisable.
1. Dissolve roughly 1 part of NaHCO3 powder (Baking Soda) forming a clear solution in the water to be tested. Only the clear part ot the solution is
to be employed.
2. Simlarly, dissolved 1.5 parts CaCl2 (DampRid) using only the clear solution.
3. Mix the solutions which in the presence of any hypochlorite will create a fine white suspension of CaCO3.
The magnitude of suspension is compared to pictures of known hypochlorite concentration based on boiled samples of the target water pretreated with
H2O2 to remove hypochlorite/HOCl using concentrations employed above. Or, carefully add a dilute acid to the washed isolated carbonate precipitate
while recording the amount of acid required until CO2 generation ceases or the precipitate vanishes. Twice the moles of consumed acid indicates the
theoretical moles of hypochlorite present in the target water.
I have used this method to sucessfully prepare HOCl from 8.25% NaOCl, albeit there is an intense white annoying CaCO3 suspension! The reaction is
actually based on a long known fact that hypochlorous acid results from the action of CO2 on an aqueous (effectively the HCO3- ion) Ca(OCl)2 forming
HOCl (along with CaCO3, see for example, https://books.google.com/books?id=d4lMAQAAMAAJ&pg=PA1324...).
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Note, if one is using NaOCl to disinfect water, I would recommend just prior to use, to lower the pH to around 6 or less using, say, filtered lemon
juice (filtered to reduce loose organic matter content), to increase disinfecting power. To quote a reference:
"At a pH of about 7.5, the amount of these two compounds is equal. In terms of oxidation potential though, hypochlorous acid is a much stronger
disinfectant than is the hypochlorite ion; about 100 times as powerful. As such, hypochlorous acid is the major disinfectant in most water treatment
practices."
As HOCl is far less stable than hypochlorite, this acidification should likely be perform within say 3 hours prior to consumption.
Further treatment is possible, in my assessment, by assuming a transition metal presence (or, low order dosing with iron and copper ions) and passing
air through the citric acid treated water/NaOCl mix with in situ formed HOCl. The aeration process could further generate reactive oxygen species
(like the hydroxyl radical, the superoxide radical anion and there interaction, source: see, for example, discussion at https://www.researchgate.net/publication/11374766_Generation... and chemistry involving transition metals, oxygen and citrate/ascorbate at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2626252/ , and the HOCl and superoxide reaction forming hydroxyl radicals at http://www.sciencedirect.com/science/article/pii/00145793938... ) to disinfect and possibly even decrease or remove the amount of contaminates
like pesticides. Note, aeration, by itself, is known to aid in the removal of volatile organics. As a final step to even remove the chlorine taste, I
would employ strong sunlight if available. This accelerates the breakdown of compounds in the water through photo-fenton (and fenton-like) paths, but
unfortunately, also HOCl as well, so consume water following treatment.
