Mixing Chemicals Together Bad!

[lmartine]

I usually scoop some spa water in my ~1l jug, add granular to that, dissolve and dump back into the spa, with a separate trip back and forth for each chemical.

Well, yesterday, I added a tblspoon of ph minus to the jug, got distracted and then added a tblspoon of lithium hypochlorite to the mix. Holy #@*! As soon as the water in the jug started to bubble and fizz and produce some nasty fumes, I realized the mistake.

What does 1 tbls of ph minus + 1 tblspoon lithium h. + 1l water produce exactly?

[Whoneedsavacation]

I'm not sure exactly, we need chem_geek or one of his peers for that, but chlorine gas is a definite possibility and potentially lethal. Kids, don't do this at home!

Seriously, people have died from throwing too many unused household cleaning products down the drain at once, let alone concentrated reagents. The classic one is ammonia and chlorine bleach.

[Dnepr Dave]

Yeah, that was chlorine gas you made, don't do it again!

Ph minus is an acid, mix an acid with Lithium or Sodium hypochlorite will make chlorine gas.

Dave

[chem geek]

[EDIT] I wrote this while Dave was posting above. Sorry for the redundant info. [END-EDIT]

You produced chlorine gas.

OCl^- + Cl^- + 2H⁺ ---> Cl₂(g) + H₂O

Hypochlorite Ion + Chloride Ion + Hydrogen Ion ---> Chlorine Gas + Water

Both sodium hypochlorite and lithium hypochlorite contain chloride (salt) since they are manufactured by adding chlorine gas to a solution of sodium hydroxide (lye) or lithium hydroxide respectively.

You never want to mix acid with any source of chlorine. If you had done so with some other concentrated forms of chlorine such as Cal-Hypo or Trichlor, you could have started a fire as well as produced chlorine gas since the reaction generates heat and be self-sustaining (in concentrated form).

Richard

[lmartine]

Thanks for the info everybody.

Is there potential for chlorine gas to be produced under normal circumstances (ie, chemicals added separately to ~1600l of water)?

Do you need to worry about timing the addition of chemicals?

[chem geek]

Thanks for the info everybody.

Is there potential for chlorine gas to be produced under normal circumstances (ie, chemicals added separately to ~1600l of water)?

Do you need to worry about timing the addition of chemicals?

No, not really, unless the water is still and without circulation and you add one very quickly after the other. If you add the chemicals slowly over a return flow at the deep end with the pump running, then they get dispersed very quickly in the bulk pool water. With decent circulation, chemicals are mostly mixed throughout the pool after 15 minutes. Personally, when I've added both chlorine and acid, I just add one slowly, then add the other slowly within a minute or two with no problems whatsoever.

[Whoneedsavacation]

Wouldn't it be more accurate to say that you do make chlorine gas in the tub, but the amount is so small it's effectively zero?

So, no, a green cloud of death won't emerge from the tub, but yes the same reaction is going on, just at a low level.

[chem geek]

Wouldn't it be more accurate to say that you do make chlorine gas in the tub, but the amount is so small it's effectively zero?

So, no, a green cloud of death won't emerge from the tub, but yes the same reaction is going on, just at a low level.

Yes and no, because you are adding chlorine in the form of hypochlorite, not chlorine gas itself. If you are using bleach, then that is sodium hypochlorite so adding it to more water just dilutes it which results in some hypochlorous acid and some hypochlorite ion. In the case of Dichlor, this is chlorine attached to CYA which when dissolved in water forms hypochlorous acid. In both cases (assuming there is some CYA in the water) you end up with mostly chlorine attached to CYA plus some hypochlorous acid plus some hypochlorite ion and a negligible amount of dissolved chlorine gas. Technically, there is a very small amount of dissolved chlorine gas produced, but with 4 ppm FC and 20 ppm CYA there is nearly 4 ppm of compounds of chlorine attached to CYA, 0.05 ppm hypochlorous acid (this is the "active" chlorine), 0.07 ppm hypochlorite ion, 0.01 ppb dissolved chlorine gas (yes, that's ppb or parts per billion).

Though the dissolved chlorine gas is very volatile (0.093 M/atm), it is mostly hypochlorous acid gas that you smell (660 M/atm) since the the rate of creation of chlorine gas is somewhat slow at normal pH and chlorine concentrations in a spa.

If you smell concentrated bleach, you are mostly smelling hypochlorous acid gas. If you add acid to concentrated chlorine (remember, NEVER do this), then that produces mostly chlorine gas, possibly at fairly high concentrations. Chlorine gas is more potent because when it mixes with water in your nose (or in your tears) it is very acidic via the following reaction:

Cl₂(g) + H₂O ---> HOCl + HCl

Chlorine Gas + Water ---> Hypochlorous Acid + Hydrochloric Acid

The hydrochloric acid is a strong acid so this is very irritating or damaging to mucous membranes. If you've ever had a whiff of Muriatic Acid, you are aware at how this is far more irritating then a whiff of even concentrated chlorinating liquid (again, do NOT take intentional whiffs of these things).

Richard