July 05, 2020, 07:32:16 PM
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Topic: Calculate pH using Ionic Strength  (Read 1387 times)

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Offline AWK

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Re: Calculate pH using Ionic Strength
« Reply #15 on: April 02, 2020, 11:37:18 AM »
And now correct this value with ionic strenght of solution.
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Offline BHAVESH

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Re: Calculate pH using Ionic Strength
« Reply #16 on: April 03, 2020, 05:12:55 AM »
can you please give some hint??
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Offline AWK

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Re: Calculate pH using Ionic Strength
« Reply #17 on: April 03, 2020, 05:38:18 AM »
Calculate activity coefficients.
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Offline BHAVESH

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Re: Calculate pH using Ionic Strength
« Reply #18 on: April 03, 2020, 09:29:06 AM »
Shall I use Davies Equation?

Log[γz ]= -A* Z2 [√I/(1+ √I)]-0.3I
A = 1.82X106*[ET]-1.5
E = 60954/[T + 116] - 68.937

T = Temp in °K
I = Ionic Strength
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Offline AWK

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Re: Calculate pH using Ionic Strength
« Reply #19 on: April 03, 2020, 09:37:36 AM »
For the beginning use standard temperature 25°C.
Check your Davies equation for the correct syntax.
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Offline BHAVESH

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Re: Calculate pH using Ionic Strength
« Reply #20 on: April 05, 2020, 01:33:49 AM »
Thanks AWK

Log[γz]= -A*Z2[√I/(1+ √I)-0.3I]

I hope this is correct now. Thanks :D :D :D
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Offline BHAVESH

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Re: Calculate pH using Ionic Strength
« Reply #21 on: April 09, 2020, 08:08:02 AM »
I Calculated Activity Coefficients
Ionic Strength - 0.2499
Temp. - 25°C = 298.15°K
A Value - 0.511
E Value - 78.24

Ionic Charge            γ Value   
      1                      0.738   
      2                     0.297   
      3                     0.065   
      4                     0.008   

Now, what should be the next step?
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Offline AWK

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Re: Calculate pH using Ionic Strength
« Reply #22 on: April 09, 2020, 09:57:08 AM »
For the problem given by Borek, the ionic strength is close to 0.04.
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Offline BHAVESH

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Re: Calculate pH using Ionic Strength
« Reply #23 on: April 10, 2020, 07:09:39 AM »
Ok
Ionic Strength is 0.04 using I = 0.5ΣCiZi2
Temp. - 25°C = 298.15°K
A Value - 0.511
E Value - 78.24
For,
Ionic Charge     γ Value
       1                 0.834
       2                 0.483

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Offline AWK

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Re: Calculate pH using Ionic Strength
« Reply #24 on: April 10, 2020, 07:51:27 AM »
Now calculate pH of this solution with activity coefficients and compare with the value obtained without activities.
AWK

Offline BHAVESH

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Re: Calculate pH using Ionic Strength
« Reply #25 on: April 11, 2020, 02:38:43 AM »
Ok
Ionic Strength is 0.04 using I = 0.5ΣCiZi2
Temp. - 25°C = 298.15°K
A Value - 0.511
E Value - 78.24
For,
Ionic Charge     γ Value
       1                 0.834
       2                 0.483
Division of γ Value = 0.834/0.483 = 1.7267
K - 4.8 X 10-11
K' =4.8 X 10-11 X 1.7267 = 8.2882 X 10-11
Corrected pH = -Log[K'] = 10.082
Original pH is 10.32

Please correct me if I am wrong.
BS

Offline AWK

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Re: Calculate pH using Ionic Strength
« Reply #26 on: April 11, 2020, 02:48:15 AM »
And where is the activity of H+ ions?
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Offline BHAVESH

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Re: Calculate pH using Ionic Strength
« Reply #27 on: April 12, 2020, 02:07:38 AM »
Ok
Ionic Strength is 0.04 using I = 0.5ΣCiZi2
Temp. - 25°C = 298.15°K
A Value - 0.511
E Value - 78.24
For,
Ionic Charge     γ Value
       1                 0.834
       2                 0.483
Division of γ Value = (0.834 X 0.483)/0.483 = 0.834 (Product/Reactant)
K - 4.8 X 10-11
K' =4.8 X 10-11 X 0.834 = 4.0032 X 10-11
Corrected pH = -Log[K'] = 10.40
Original pH is 10.32

Does it mean that pH always increases when we use Ionic Strength as a correction factor, OR does it depend upon what kind of Acid, Base or salt reaction we work with???

Please correct me if I am wrong.
« Last Edit: April 12, 2020, 02:20:59 AM by BHAVESH »
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Offline AWK

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Re: Calculate pH using Ionic Strength
« Reply #28 on: April 12, 2020, 02:40:10 AM »
The value of K' is ambiguous. What exactly does it mean for you? Calculations can be made using the thermodynamic constant K. I expect a pH value very close to 10.
AWK

Offline BHAVESH

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Re: Calculate pH using Ionic Strength
« Reply #29 on: April 12, 2020, 05:07:08 AM »
What I think is that at constant temperature, ionic strength affect K value OR pH Value. When It is corrected using ionic strength, gives us actual value.

Can you please give me some hint on using thermodynamic constant K?
BS

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