[ElSeba]

Hello Everyone,

I am not a chemical engineer and the last time I had chemistry was in college 9 years ago, so please forgive any non technical lingo I may use in the following.

The manufacturer of an engine provides a two step type heavy duty radiator cleaner consisting of an acidic solution and a neutralizer as follows (verbatim):

- Acid: Mix 900 g (2 lb) of sodium bisulfate (NaHSO₄) per 38 liters (10 gal) of water (25 grams per liter).
- Neutralizer: Mix 225 g (1/2 lb) of sodium carbonate crystals Na₂CO₃ per 38 liters (10 gal) of water (6 grams per liter)

A service company is offering a different combination of chemicals that they claim will do the work too. They are planning on using:

- Acid: Citric Acid (Anhydrous) C₆H₈O₇
- Neutralizer: Sodium Carbonate (Anhydrous) Na₂CO₃

Relevant but not important: They mention that if oil/grease is present they may also use Trisodium Phosphate (Na₃PO₄). And for the neutralizer they also use a solution of Sodium Nitrite (NaNO₂).

This company is not providing us with the exact concentrations they use (mainly because they are not very thorough) and so I am trying to come up with an Engineering reasoning as to concentrations for the Acid and Neutralizer solutions with the chemicals they offer.

1- What would the equation I need to balanced be in order to obtain the right amount of neutralizer (please use the given concentrations for the solutions to explain it).

2- If I need to calculate anions concentrations or pH what would these be for the second set of chemicals?

3- Anyone has experience in cooling system cleanup that can give me an idea of how well will the citric acid clean rust and scale?

Thank you all very much and I hope I formulated the question clearly enough.

Have a nice day!

ElSeba

[Borek]

Not sure if I understand what you are trying to do. Amount of acid left after cleaning depends on the amount of scale dissolved, not knowing how much scale was dissolved you can't predict amount of neutralizer required. You may at best evaluate maximum amount.

[ElSeba]

You are totally right. I thought of that but I didn't know how to include it.

The solutions provided then probably take into account some estimate of scale to be removed so I guess the neutralization, without considering the effect of actually removing scale, is incomplete. If the neutralization is incomplete, can that be expressed as a metric? For example, can we say XX moles/g/liters of the acid solution are not neutralized.

If so, I would just use the same value when calculating concentrations using the new chemicals. I know this is probably not technically correct, but I want to at least have a ball-park value that I can use. Minor adjustments can be obtained afterwards checking the pH of the system.

Thanks for the quick answer!!!

ElSeba

[Borek]

What is the neutralization procedure? Is it "add given amount" or "add till solution gets neutral"?

[ElSeba]

What is the neutralization procedure? Is it "add given amount" or "add till solution gets neutral"?

The neutralization works as "add till solution gets neutral".
However, I would like to have an idea of a way to estimate the necessary amount of neutralizer. Maybe based on the pH of the solution after cleaning the scale.

[Borek]

I would like to have an idea of a way to estimate the necessary amount of neutralizer. Maybe based on the pH of the solution after cleaning the scale.

It won't work. pH depends on many factors and doesn't tell anything about buffer capacity of the solution.

You can get rough estimate of maximum amount assuming citric acid reacts with carbonate in 2:3 molar ratio.

[ElSeba]

It won't work. pH depends on many factors and doesn't tell anything about buffer capacity of the solution.

You can get rough estimate of maximum amount assuming citric acid reacts with carbonate in 2:3 molar ratio.

OK, so I was way off with what I wanted in the first place. Let me change the question a little bit then.

1- You said citric acid reacts with sodium carbonate in approximately a 2:3 molar ratio. What would be an approximate ratio for Sodium Bisulfate (instead of Citric Acid)?

2- What are the product of the reaction in both cases?
    a- Citric Acid solution + Sodium Carbonate solution
    b- Sodium Bisulfate + Sodium Carbonate solution

3- What would change if instead of a Sodium Carbonate solution I have a solution with Sodium Carbonate and Sodium Nitrite?

Once again, thanks a ton Borek!!

ElSeba

[Borek]

You said citric acid reacts with sodium carbonate in approximately a 2:3 molar ratio.

Not approximate, exact. This is a simple high school stoichiometry.

What would be an approximate ratio for Sodium Bisulfate (instead of Citric Acid)?

As for the rest of your questions - these are all simple acid base reactions, nothing fancy, producing salt and water. Carbonate can react with two H⁺ and decomposes to water and CO₂.

If you will brush your chemistry (on the very basic level) you will be easily able to calculate everything on your own. Try, ask in the case of problems. This way you will not need to ask for help each time something changes in your setup.

These may help:

http://www.chembuddy.com/?left=balancing-stoichiometry&right=stoichiometric-calculations

http://www.titrations.info/titration-calculation

[ElSeba]

Thanks for your suggestions Borak.

Not approximate, exact. This is a simple high school stoichiometry.

The way you worded it in the previous message was:

You can get rough estimate of maximum amount assuming citric acid reacts with carbonate in 2:3 molar ratio.

That rough estimate part made me think the balance was not exactly 2:3 molar

As for the rest of your questions - these are all simple acid base reactions, nothing fancy, producing salt and water. Carbonate can react with two H⁺ and decomposes to water and CO₂.

If you will brush your chemistry (on the very basic level) you will be easily able to calculate everything on your own. Try, ask in the case of problems. This way you will not need to ask for help each time something changes in your setup.

I don't want to justify my lack of knowledge of chemistry, but this is nothing even close to what I do on a daily basis. I am a mechanical engineer working with compressor packages. This was just thrown on my desk on the lack of better resources.

Also, things don't usually change in this setup because usually in industry we go with what the manufacturer says. In this case, the company doing the maintenance of our engine uses something that does not match exactly the manufacturer's recommended procedure (and the manufacturer is taking for ever to give us an answer whether we can use this or not) so I wanted to see if I could figure out what the difference was.

So, maybe I asked this question in the wrong forum or used the wrong wording, but if it is such a simple reaction, the equation would have helped me greatly. Someone on a different forum gave me the following reaction equations for both combinations:

1:   2 NaHSO₄ + Na₂CO₃ = 2 Na₂SO₄ + CO₂ + H₂O
2:   2 C₆H₈O₇ + 3 Na₂CO₃ = 2 C₆H₅O₇Na₃ + 3 CO₂ + 3 H₂O

That is not all I need, but gives me a ball park of how much neutralizer I would need in case I needed to neutralize all the acid I'm using. Considering I will be removing some scale and rust, I will definitely need less than that value. And still in the air is the question as to what concentration of citric acid can match the results of the manufacturer's concentration of sodium bisulfate.

Thanks.

ElSeba

[Borek]

You can get rough estimate of maximum amount assuming citric acid reacts with carbonate in 2:3 molar ratio.

That rough estimate part made me think the balance was not exactly 2:3 molar

I see it could be confusing. I was aiming at the fact that all concentrations given seem to be rather approximate, so even if you know exact stoichiometry, calculated results are closer to the educated guess than to precise answer.

1:   2 NaHSO₄ + Na₂CO₃ = 2 Na₂SO₄ + CO₂ + H₂O
2:   2 C₆H₈O₇ + 3 Na₂CO₃ = 2 C₆H₅O₇Na₃ + 3 CO₂ + 3 H₂O

If you compare them with what I wrote, you will see that's the same. Carbonate reacts with acid producing water and carbon dioxide.
 

And still in the air is the question as to what concentration of citric acid can match the results of the manufacturer's concentration of sodium bisulfate.

This is not easy, as these solutions will behave differently. I would bet molar concentration of citric acid can be lower than molar concentration of bisulfate, but by how much is not that obvious, this is a subtle equilibrium involving three dissociation steps of citric acid and two dissociation steps of carbonic acid. In the simple terms citric acid should be able to consume three times more scale per mole than bisulfate, but I doubt reaction will proceed to the end, so you need some more.