Thread: Coolant
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Unread 10-30-2002, 04:54 AM   #14
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So you just added something strongly basic to water (pK = 14), and the pH dropped? Reasonableness?

(I think you want to remove a proton when writing a reaction for the dissociation and not release an OH-)

HOC2H40H <--> -OC2H4OH + H+ (logKa1 = -14)

Not so simple in real world though.

Consider the equilibrium between copper ions and aluminum ions and the glycol as well (that will affect the speciation of the glycol). I dont have stability constants for such at fingertips; dont know what concentrations for metals is "normal".

Another complication with neutral/alkaline pH:

Don't forget to consider the solubility of CO2.

CO2(g) <-->CO2(l)
CO2(l) + H2O <--> H2CO3*
H2CO3* <--> H+ + HCO3^- (logKa1 = -6.3)
HCO3- <--> H+ + CO3^2- (log Ka2 = -10.3)

You'll find quite a lot of total dissolved CO2 (H2CO3* + HCO3- + CO3^2-) at pH 8 or higher. You can solve the above by considering that the relationship between CO2(g) and CO2(l) is related to Pco2 and the Henry's Law constant for CO2.

Not going to be able to solve this without an iterative approach. Mineql is a free download and not too bad (DOS but works mostly in XP/2k)
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