Reducing PH of overflow tank

[Dean137]

HI all, long time reader first time poster here

 

I have a question and looking for some help. Its been along time since I used any chemistry I learned while doing my degree but for the life of me I cant figure out this.

 

I have a 300L overflow tank with a PH of 13 it needs to be reduced to below 9 before it can be disposed of, I have 1M HCl available how much HCl do I need to add to achieve below PH9.

 

Thank you for any help

Edited May 26, 2016 by Dean137

[foxy john]

I'm afraid you will just have to try it and see. It all depends on what is in the tank making the pH high. Just do a test with a small volume and see what happens.

[Dean137]

Should have probally put that info in aswell

 

The cleaning solution is NaOH and its diluted down with water to the required strength, and i made a typo and its a 300L tank

[John Cuthber]

Very roughly, at pH 13 assuming it is all NaOH you must have a solution that's about 0.1 M and to neutralise it you would need about a tenth of it's volume of the HCl (which is roughly ten times more concentrated). That means about 30 litres.

 

A better approach might sometimes be to ask how much NaOH you added in the first place.

Each gram of NaOH will need 25 ml of 1M HCl to neutralise it.

 

In any event, beware that the mixture will get a bit warm, and more importantly, that it will probabaly fizz and foam.

(because the NaOH will have picked up CO₂ from the air to make Na₂CO3 and when you add acid that will decompose and give the CO₂ back again.)

Try it with 300 ml and 30 ml of acid + see how far that gets you.

Also, remember that it is nothing like linear.

The pH vs added acid will look something like the Titration curves for strong acid v strong base here

 

http://www.chemguide.co.uk/physical/acidbaseeqia/phcurves.html

 

It drops like a rock, just about where you want to control it.

[Dean137]

I tired it yesterday befor eyour post with 100ml and the pH dropped to 4 after 2ml of HCl

[foxy john]

You have cracked it! Really hard to control the exact pH.