July 09, 2025, 06:18:43 AM
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Topic: Nitric Acid Concentration  (Read 2935 times)

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Offline Matt.Swearingen03

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Nitric Acid Concentration
« on: July 01, 2025, 03:20:21 PM »
My company has a passivation procedure for some metal parts where we have 2 tanks of 24% concentration and 34% concentration. We are going to test the concentrations tomorrow using specific gravity to see if we need to add acid or water in order to get back to that desired concentration. My question is is my math for determining how much we need to add correct. Be warned this is 2 mechanical engineers in lab coats attempting to work on this project so it very well could be off.

Ci*Vi + Ca*Va = Cf*(Vi+Va)
So Va = Vi*((Cf - Ci)/(Ca - Cf))
Where Va is the volume added of acid or water, Cf is desired concentration Ci is initial concentration Ca is Acid concentration Vi is volume initial.

Any help is appreciated.

Offline Borek

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Re: Nitric Acid Concentration
« Reply #1 on: July 01, 2025, 04:49:07 PM »
It is not clear how Ca and Ci relate to 24% and 34%.

In general your equation

Ci*Vi + Ca*Va = Cf*(Vi+Va)

is reasonably OK, but it ignores fact volumes are (in general) not additive (Vf is not guaranteed to be equal to sum of Vi and Va). Masses are additive though, which makes the problem solvable with the help of the density table.

Depending on how accurate result you need this approach can be good enough though.

If you need really accurate result try to download the concentration calculator - it does exact calculations for mixing (if memory serves me well density table for nitric acid is built in). Free trial version should be enough for you to check if the numbers are OK.

I can help with the program if something is not clear.
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