Accident at factory, how to solve it?

Kyoma

In an accident at a factory, some nitric acid was split.

Which substance then, when added in excess, would be the best chemical to neutralise the acid without leaving an alkaline solution?

Calcium carbonate or sodium carbonate?

I picked sodium carbonate but calcium carbonate is the best choice. Why? Is it got to do with it being insoluble in water?

Nemus

Personally I recommend that you use an absorbent like vermiculite first to remove the bulk of the acid and to contain the spill as quickly as possible. I agree with calcium carbonate as a second line of defence but it reacts very vigorously (although not as violently as sodium carbonate which is probably the answer to your question) and you get a very nasty smoke of nitric acid aerosol which is not only unhealthy (you need a gas mask anyway) but it will also corrode everything in the room very badly too. Believe me, I have tried this.And don't forget to scrub the floor with calcium carbonate and water several times. And your clothes goes directly into the washing machine. Some of them may be saved. Maybe.

Borek

Hint to simple answer: think about sodium and calcium carbonates solubilities.

Kyoma

From what I know, calcium carbonate is insoluble but sodium carbonate is soluble. Why does solubility matter?

Studiot

Yes!


( How do you get a left over alkali solution with an insoluble compound?)

Note Calcium carbonate is slightly soluble.

Q: Why do you not want a left over alkaline solution?

A: Because that might also be dangerous.

Q: What happens if sodium carbonate solution is poured onto concrete?

A the solution attacks the concrete and weakens it.

Q: What happens if calcium carbonate solution is poured onto concrete?

A: You get a white chalky residue after the water has evaporated. The concrete is not attacked.

Kyoma

I was thinking; is it because the nitric acid itself contains a small amount of hydroxide ions, thus the addition of sodium carbonate would form a small amount of sodium hydroxide, which is alkaline?

Borek

No. Have you heard about hydrolysis? Brønsted-Lowry theory of acids and bases? Do you know that CO₃^2- is a base?

Kyoma

I'm still unable to understand it. Yes, I have checked hydrolysis on Wikipedia and I think my previous post is correct. I have no idea, seriously.

Borek

What is the characteristic reaction of a Bronsted base? Or - in other words - what is the property that makes something a Bronsted base?

Assuming CO₃^2- is a Bronsted base - can you try to write reaction equation with water? There will be two products.

Kyoma

Okay, you caught me.

I have no idea what is Brønsted-Lowry theory. I have tried to check it on Wikipedia and other websites but I have no idea what they are saying.

This is the two equations I could come out with:

Sodium carbonate plus nitric acid gives you sodium nitrate, carbon dioxide and water.
Calcium carbonate plus nitric acid gives you calcium nitrate, carbon dioxide and water.

???

Studiot

Check out which nitrate is more explosive, sodium or calcium.

Note this is extra information and not to do with the original question, which Borek is handling.

Borek

Problem is not in the nitric acid, but in the carbonate ion - it changes pH of the solution, as it reacts with water. Try to write reaction equation - as I wrote, you start witch CO₃^2- and water, and CO₃^2- is a weak Brønsted base, which means it will accept a proton (stealing it from the water molecule).

Now, think if that can happen if you add calcium carbonate to water?

Borek

How is it related to the solution pH?

SpectraCat

Here is another hint ... the issue is not the neutralization reaction ... seems like you have done that correctly from your post #10. The issue is that you are adding EXCESS carbonate solution, so after the neutralization reaction is over, there will be calcium carbonate left over. That is why Borek is guiding you to think about the reaction of carbonate with water.

Kyoma

Okay, I think I kinda get it. I will try.

CO₃^2- + H₂O -------> HCO₃^- + OH^-

I think this is the equation. So, if you add calcium carbonate to water, the calcium ions would be bonded to the hydroxide ions above to form calcium hydroxide. Am I right?

SpectraCat

Yup! That is the correct interpretation [EDIT: I should point out that it is correct only for the carbonate ions that are dissolved in solution. You also need to take the stoichiometry of the problem into account, since carbonate and hydroxide ions have different charges]. Do you now understand why the relative solubilities of sodium hydroxide and calcium hydroxide are important for this case?

[EDIT: whoops! I really meant sodium carbonate and calcium carbonate in the last sentence above. The solubilities of sodium hydroxide and calcium hydroxide are also relevant to the problem, but aren't as important.]

Studiot

Are you sure? You started this thread (correctly) noting that calcium carbonate is (nearly)insoluble.

So start at the beginning.

How would you add sodium carbonate or calcium carbonate to the nitric acid to neutralise it?

In solution or as a solid (powder)?