[OzWaz]

I have 1000mls of sodium hypochlorite 16 % solution which I need to add to water Can some one tell me how many mls of hydrochloric acid 29% solution I need to add to the water to maintain the receiving products current pH?

Thanks   

[Hunter2]

Danger: Don't add HCl to it, because you will create chlorine gas. Use diluted sulfuric instead!!!!
Not soluble because we don't know which pH you want to get.
Also specific gravity of the Hypo chlorite solution is unknown.

[OzWaz]

No, there is no danger, the receiving body of water has about 14,000l. I do this often. The Na(OCl) goes first but I have to readjust the pH back to the set level of 7.2 by trial and error a few mills at a time using the HCl.

Would like to know how much HCl to add (from a chemist perspective) up front - Thus making the process a lot easier 

[Hunter2]

You didn't told, that you add to a container with 14000 l, probably a swimming pool. Then its no danger. If you add the Hypochlorite, what pH you receive? If you know this you can calculate back to pH 7.2

pH = -lgc(H⁺)  and pOH =  -lgc(OH^-)
You can do the test you take bucket ad 14 liter water and add 1 ml of your solution and check the pH.

[magician4]

(...)but I have to readjust the pH back to the set level of 7.2 by trial and error a few mills at a time using the HCl.

I would strongly recommend to keep up with this procedure, as the buffer capacity (most likely from hydrogencarbonate)*⁾ of your "untreated" 14 m³ of water (i.e. before you add the NaOCl) is unknown, but relevant if we're talking pH 7.2 as target. Furthermore, you're close to the buffer point of OCl^- (pKa HOCl 7.54) ,  which makes calculations a bit more complicated, still

Ignoring the influence of HCO₃^-, as a theoretical exercise you would approach such a calculation  by using the Henderson-Hasselbalch equation with NaOCl
but then again: in reality you can't ignore it, as  HCO₃^- is an ampholyte (pKa1 6.35 , pKa2 10.33), hence forms kind of a buffer in it's own right (pH ~ 8.3),  which additionally is (as you reported pH 7.2) a bit on the acid side due to additional CO₂ in the game.

so: you might wish to add the bulk of HCl you usually add in one serving, yes, but then you'd better approach the desired final pH in small steps, as the initial buffer capacity of your water is unknown, and also might be different with every refill of your pool


regards

Ingo





*⁾
I am naming this species as a representative of all those carbonate / carbondioxide ... equilibriums involved, as calcium hydrogencarbonate most probably is the major source of the pH in your freshwater

[curiouscat]

Uniformly dissolving ~1000 ml in 14,000 L of water must be a nightmare of a mixing problem..