[scientizscht (OP)]

Hello

I have bought a buffer salt to add to a water container.

The pKa of the salt is 7.2. Does that mean that after I add the salt to the water, the pH will be 7.2?

If I want to adjust that pH, what materials can I use to do that? NaOH and HCl are dangerous so I want to use safer alternatives preferably something I can get from the supermarket like vinegar and baking soda.

Thanks!

[Bored chemist]

It depends.

The pKa of the salt is 7.2. Does that mean that after I add the salt to the water, the pH will be 7.2?

Probably not.

[scientizscht (OP)]

It depends.

The pKa of the salt is 7.2. Does that mean that after I add the salt to the water, the pH will be 7.2?

Probably not.

How can I calculate the pH that will be formed and what materials can I use to adjust it?
The salt is di-sodium hydrogen phosphate dihydrate at 150mM.

[Bored chemist]

How can I calculate the pH that will be formed

https://en.wikipedia.org/wiki/Henderson%E2%80%93Hasselbalch_equation

what materials can I use to adjust it?

It depends.
As usual, you have not bothered to give us enough information to work on.
This is annoying from my perspective and unproductive from yours.
Why do you keep doing it?

[scientizscht (OP)]

How can I calculate the pH that will be formed

https://en.wikipedia.org/wiki/Henderson%E2%80%93Hasselbalch_equation

what materials can I use to adjust it?

It depends.
As usual, you have not bothered to give us enough information to work on.
This is annoying from my perspective and unproductive from yours.
Why do you keep doing it?

"The salt is di-sodium hydrogen phosphate dihydrate at 150mM".
That's all. I need this to make it neutral.

[Bored chemist]

I need this to make it neutral.

That's the bit of information you didn't supply before.

So why did you say this?

"The salt is di-sodium hydrogen phosphate dihydrate at 150mM".
That's all.

Anyway, in this case baking soda will work. Other bases would also work, so you could use ammonia or trisodium phosphate or even something like potassium citrate.

However, I still don't actually know what you want to achieve, so I can't fully answer the question.
Do you want to keep the phosphate concentration constant or the sodium concentration?

You probably don't know that answer to that question. I can't tell you how to proceed until you answer it so, once again, you haven't got (and can't get) the information you are looking for because you are too stubborn to answer a simple question.

What are you trying to achieve?


Why do you always do this?

[scientizscht (OP)]

I need to prepare the above buffer solution at the above mentioned concentration.

Then I need to adjust its pH to be 7 hence I asked how to achieve that.

The rest, ie what I will be doing next with the solution is already defined in a known protocol so I don't mention it since I don't have any particular question around that.

The protocol says to add HCl or NaOH to adjust the pH of the buffer solution. That's the only bit of the protocol that puzzles me because it's not easy to get HCl and NaOH hence the question.

[Bored chemist]

Odd. I never had much difficulty getting NaOH and HCl from the hardware store.

However, I'm sure you can see how adding things to a 150 mM solution means that it won't be 150 mM any more.
You could use a 150 mM solution of trisodium phosphate. That way you keep the phosphate concentration at 150 mM at the cost of having a different sodium concentration.

Because you stubbornly refuse to say what you are going to do with it, I can't say which approach would work better.

I don't mention it since I don't have any particular question around that.

Yes you do. You just don't know enough chemistry to realise that you have a question.
Your question is "which option is better, to maintain the phosphate concentration at 150mM or to maintain the sodium concentration?"