# Reduce PH of water using Hydrochloric Acid

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Hi Guys,

I have a problem and I need your assistance.

I have 59000 litres of stormwater trapped in a concrete sediment pond. It currently has a ph of 11 and I need to reduce this to no greater than 9 prior to discharge into bio basin. I have Hydrochloric Acid available at a concentrate of 33%.

My question is how much of this Acid will i require to treat the 59000 litres to reduce the ph level from 11 to 9.

I can assure you this is not an exam question from my sons grade 6 chemistry class it is a real world problem a poor old layman like myself would like to solve but im too old and tired. Sorry.

Any assistance would be appreciated.

I have had those at work come up with figures like .0076ml, 67 litres , 445 litres and one over 1000ltrs of acid required.

Can I leave it to you guys to solve this one for me.

Many thanks

Rod

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pH=11 means 10-3 mol OH- per litre. 59,000 L water contain 59 mol OH-, to be neutralized by 59 mol of pure HCl or 2.15kg. If 33% is a mass concentration, it takes 6.5 kg, or about 6 L.

pH=9 or 10-5 mol OH- per litre needs you to neutralize with 1% accuracy, but the pH=11 measure isn't so accurate, so you need to mix and monitor the pH during the operation.

If your pond is made of concrete, and if this has made pH=11 (which needs a good reason!), the pH may drift further over time and when the neutralization is conducted.

Just wait until John Cuthber passes by. If I botched that, he will let it notice.

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My ears were burning.

Most of the alkali present may be carbonate and silicate rather than hydroxide.

Good luck with getting good mixing on that scale.

Since you can't be sure what the stuff you are trying to neutralise actually is, the calculation is a bit suspect.

I'd try adding 6 litres of 33% HCl and stirring it, waiting a day or so and then measuring the pH again.

It's perfectly possible that the pH will still be about 11

That's because the water will dissolve some silicates and carbonates from the concrete and that will raise the pH again.

Essentially, whatever calculations we come up with, you are going to have to do the experiment with the actual tank full of water..

It might be easier to try with 1 litre of the water and titrate that with the acid - say 1 ml at a time- until it's near neutral. That will give you a good idea of where to start.

Do you, by any chance, have a plastic lined pond you can put the stuff in, rather than the concrete?

If you can, then at least you won't be trying to neutralise all the concrete.

Even working 1 tonne at a time in an IBC might be a better bet than trying to work on the whole pond full.

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and don't forget to add the acid SLOWLY, not all at once!

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As we know the

pH + pOH = 14 , if you know the concentration of thesoluton you may calculate easily pH of solution as well as pOH.

Here is formula for the determination of pH,

pH = log ( H+)

and you may put the determined value of pH in the equation of pH + pOH = 14 , and get the value of pOH.

We can reduce the pH of the soultion by adding any kind of acid, if we use acid its pH may reduce to1 or even 0, it means the concentration of Hydrogen ions will be increased.

You may detect the pH of the solution by unversal indicator paper and pH meter.

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As we know the

pH + pOH = 14 , if you know the concentration of thesoluton you may calculate easily pH of solution as well as pOH.

Here is formula for the determination of pH,

pH = log ( H+)

and you may put the determined value of pH in the equation of pH + pOH = 14 , and get the value of pOH.

We can reduce the pH of the soultion by adding any kind of acid, if we use acid its pH may reduce to1 or even 0, it means the concentration of Hydrogen ions will be increased.

You may detect the pH of the solution by unversal indicator paper and pH meter.

Do you think that helped in any way?

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This is correct formula to culclate the pH of the solution.

pH= - log ( H+)

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No it isn't- or at least not with the usual conventions.

pH= -log [H+]

is better and, btw, the word is calculate.

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[H+] shows the concentration of hydrogen ion.

pH is negative log of hydrogen ion concentration

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[H+] shows the concentration of hydrogen ion.

pH is negative log of hydrogen ion concentration

Why do you bother to state the obvious?

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!

Moderator Note

Parshotam,

Please try and remain on topic when responding to threads. None of what you have said is helpful to the OP and does nothing the answer the question. If you don't understand the question, perhaps it would be better to ask for clarification or to read the responses.

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• 7 years later...
On 7/24/2013 at 4:09 AM, dirtyamerica said:

and don't forget to add the acid SLOWLY, not all at once!

I know this is an ooooold post, but why shouldn't one add all the required acid at once?

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43 minutes ago, NotYou said:

I know this is an ooooold post, but why shouldn't one add all the required acid at once?

It is a safety issue.

If you add concentrated acid to water, the reaction can be so violent that the mixture spits drops of concetrated acid about.
This is because the acid heat of reaction heats the liquid in direct contact and can be enough to generate steam which propels the drops.

This effect is even more pronounced if you try to do it the other way round ie add water to acid, which is why you should always add strong acid to water, a small amount at a time.

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