Neutralization Solution Calculation

[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

[expert]

Let’s start with the reaction of neutralization:

2 NaHSO₄ + Na₂CO₃ = 2 Na₂SO₄ + CO₂ + H₂O

Basically that means 2 mols of NaHSO₄ can be neutralized by 1 mol of Na₂CO₃
Calculating molecular weights: NaHSO₄ 120 g/mol; Na₂CO₃ 106 g/mol
So for complete neutralization you need to add 106 g of Na₂CO₃ to 2*120 = 240 g of NaHSO₄. Calculate proportionally your situation. Make sure the reagents are anhydrous. Sodium carbonate can come in a decahydare form. decahydrate Na₂CO₃.10H₂O (soda crystals, washing soda) is formed in large transparent crystals. Molecular weight is higher: Na₂CO₃*10H₂O is 286 g/mol so recalculate accordingly.
Citric acid http://en.wikipedia.org/wiki/Citric_acid can react with different amounts of Na₂CO₃ forming a buffer. Complete and maximal neutralization goes by the following equation:
2 C₆H₈O₇ + 3 Na₂CO₃ = 2 C₆H₅O₇Na₃ + 3 CO₂ + 3 H₂O
or 2* 192 g (or 2*210 for monohydrate) requires 3*106 g (or 3*286 g for dehydrate) of Na₂CO₃ for complete neutralization.
Citric acid forms complexes with iron and many other metals and therefore it’s excellent rust remover.

Na₃PO₄ is a known good grease remover but not much for the rust elimination or prevention. NaNO₂ is not neutralizing Na₃PO₄ but rather acts as a rust inhibitor.
http://en.wikipedia.org/wiki/Corrosion_inhibitor

[ElSeba]

Let’s start with the reaction of neutralization:

2 NaHSO₄ + Na₂CO₃ = 2 Na₂SO₄ + CO₂ + H₂O

Basically that means 2 mols of NaHSO₄ can be neutralized by 1 mol of Na₂CO₃
Calculating molecular weights: NaHSO₄ 120 g/mol; Na₂CO₃ 106 g/mol
So for complete neutralization you need to add 106 g of Na₂CO₃ to 2*120 = 240 g of NaHSO₄. Calculate proportionally your situation. Make sure the reagents are anhydrous. Sodium carbonate can come in a decahydare form. decahydrate Na₂CO₃.10H₂O (soda crystals, washing soda) is formed in large transparent crystals. Molecular weight is higher: Na₂CO₃*10H₂O is 286 g/mol so recalculate accordingly.
Citric acid http://en.wikipedia.org/wiki/Citric_acid can react with different amounts of Na₂CO₃ forming a buffer. Complete and maximal neutralization goes by the following equation:
2 C₆H₈O₇ + 3 Na₂CO₃ = 2 C₆H₅O₇Na₃ + 3 CO₂ + 3 H₂O
or 2* 192 g (or 2*210 for monohydrate) requires 3*106 g (or 3*286 g for dehydrate) of Na₂CO₃ for complete neutralization.
Citric acid forms complexes with iron and many other metals and therefore it’s excellent rust remover.

NA₃PO₄ is a known good grease remover but not much for the rust elimination or prevention. NaNO₂ is not neutralizing Na₃PO₄ but rather acts as a rust inhibitor.
http://en.wikipedia.org/wiki/Corrosion_inhibitor

Wow, that was exactly what I needed. Thanks a lot expert!

There's only one last thing I would like to know. If I have a solution with a given concentration of Citric Acid what would the reaction be in presence of a solution of Sodium Nitrite and Sodium Carbonate?

Thanks again!

ElSeba

[expert]

Citric acid is not effective rust remover after neutralization. Keep this in mind. Try to avoid mixing citric acid with sodium nitrite. That reaction will produce toxic and corrosive vapors of nitrogen oxides: brown gas NO₂ and NO http://www.ace.mmu.ac.uk/eae/air_qualit ... oxide.html

It's OK to mix sodium nitrite with neutralized mixture of citric acid and sodium carbonate. Just avoid acids with NaNO₂. If you need to use sodium nitrite as a rust inhibitor, add it after flushing and neutralizing citric acid.