pH question
pH question
(OP)
Hi,
I haven't done chemistry in a long time so this is probably quite basic but I just want to check my working for a pH problem:
There are two streams that enter a mixing tank. Stream 1 flows at 92 m3/d and has a pH of 11. Stream 2 flows at 105.6 m3/d and has a pH of 2.45. I need to know what will be the resulting pH in the mix tank after the streams combine.
How I got my answer:
H+ + OH- <-> H2O
I need to find the final H+ concentration
stream 1)
Assuming concentration of H+ is insignificant
mol of OH- per day = (10^-(14-11))*92.5 = 0.0925
stream 2)
Assuming concentration of OH- is insignificant
mol of H+ per day = (10^-(2.45))*105.6 = 0.3747
H+ and OH- react
0.3747 - 0.0925 = 0.282 mol of H+ after reaction
resulting pH = -log10(0.282/(92.5+105.6)) = 2.846
I haven't done chemistry in a long time so this is probably quite basic but I just want to check my working for a pH problem:
There are two streams that enter a mixing tank. Stream 1 flows at 92 m3/d and has a pH of 11. Stream 2 flows at 105.6 m3/d and has a pH of 2.45. I need to know what will be the resulting pH in the mix tank after the streams combine.
How I got my answer:
H+ + OH- <-> H2O
I need to find the final H+ concentration
stream 1)
Assuming concentration of H+ is insignificant
mol of OH- per day = (10^-(14-11))*92.5 = 0.0925
stream 2)
Assuming concentration of OH- is insignificant
mol of H+ per day = (10^-(2.45))*105.6 = 0.3747
H+ and OH- react
0.3747 - 0.0925 = 0.282 mol of H+ after reaction
resulting pH = -log10(0.282/(92.5+105.6)) = 2.846





RE: pH question
Interesting perspective on things though.
RE: pH question
Please, correct me if I'm wrong.
RE: pH question
25462, I don't think you can use your method because you didn't take into account H+ and OH- reacting together. It is valid if you mix two acids and neutralisation doesn't occur. Pretty close to my answer anyway.
RE: pH question
RE: pH question
Two pieces of information are necessary to calculate the molarity of a solute in a solution:
• The moles of solute present in the solution.
• The volume of solution (in liters) containing the solute.
To calculate the pH of an aqueous solution you need to know the concentration of the hydronium ion in moles per liter (molarity). The pH is then calculated using the expression:
pH = - log [H3O+].
Example: Find the pH of a 0.0025 M HCl solution. The HCl is a strong acid and is 100% ionized in water. The hydronium ion concentration is 0.0025 M. Thus:
pH = - log (0.0025) = - ( - 2.60) = 2.60
RE: pH question
RE: pH question
RE: pH question
• whether there is a buffer effect present
• that the streams are thoroughly mixed
• that there is no additional reaction between the acidic and the alkaline streams such as, for example, the release of CO2.
• that the reaction has been carried out at 25oC for pKw = 14. Its variation with temperature is:
at 0ºC it is 14.94
at 10ºC it is 14.53
at 20ºC it is 14.16
at 30ºC it is 13.83
at 40ºC it is 13.53
Therefore, your conclusion of actually measuring the final pH is IMHO the correct one.