[Matt.Swearingen03]

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.

C_i*V_i + C_a*V_a = C_f*(V_i+V_a)
So V_a = V_i*((C_f - C_i)/(C_a - C_f))
Where V_a is the volume added of acid or water, C_f is desired concentration C_i is initial concentration C_a is Acid concentration V_i is volume initial.

Any help is appreciated.

[Borek]

It is not clear how C_a and C_i relate to 24% and 34%.

In general your equation

C_i*V_i + C_a*V_a = C_f*(V_i+V_a)

is reasonably OK, but it ignores fact volumes are (in general) not additive (V_f is not guaranteed to be equal to sum of V_i and V_a). 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.