Estimating pH
Estimating pH
(OP)
Hello,
I have two process streams both are water, one is rain water from a coal storage area with an estimated pH of 3 and the other is rain water from paved areas such as roads with an estimated pH of 5.6.
My question is if I know the flow rates of each stream, is there any way of estimating the pH of the combined streams.
Regards,
athomas236
I have two process streams both are water, one is rain water from a coal storage area with an estimated pH of 3 and the other is rain water from paved areas such as roads with an estimated pH of 5.6.
My question is if I know the flow rates of each stream, is there any way of estimating the pH of the combined streams.
Regards,
athomas236





RE: Estimating pH
However, you deal with almost pure water, so the buffer capacity of each stream should be low, and I think that, for an estimate, the following is OK.
The major assumption is that you have no components buffering.
A buffer is some component or mix that prevents pH from changing quickly.
at pH 3 you have 1.e-3 mol/l H+ (0.001)
at ph 5.6 you have 1.e-5.6 mol/l H+ (2.5e-6)
mixing Q1 of pH3 with Q2 of pH 5.6 yield a concentration of (Q1&Q2 same unit, both are mostly water)
C=(Q1*1.e-3 + Q2*1.e-5.6)/(Q1+Q2)
and the pH is -log10(C)
ex 50% 50% Q1=1 Q2=1 m3
C=0.00501 mol/l H+ pH=3.3=-log10(0.005)
RE: Estimating pH
PH=3.3 was correct sorry
RE: Estimating pH
Thank you very much for your assistance.
Best Regards,
athomas236
RE: Estimating pH
As explained by siretb, assuming no buffering effects, a pH≅5.6 in rain water at ambient temperatures, points to the possible presence of CO2 that partly dissociates to form both weak carbonic acid and bicarbonate ion in a ratio of about 5.5 to 1.
At pH<4,0 there is practically no bicarbonate ion.
A pH≅3 indicates the possible presence of other stronger mineral acid moieties as well.
Mixing both water streams may free some CO2 releasing it from the higher-pH water resulting in a somewhat higher-pH mixture than would be obtained just by applying the above-mentioned mixing rule.
IMHO, measuring the pH of samples of various mixtures might give you a better picture of the expected pH.