The Student Room Group
Uni students - Complete our survey >>
Uni students - Complete our survey >>
Uni students - Complete our survey >>

ionic activity, a+-

may i know how to calculate the ionic activity of an ion, a+-, given the ionic strength, I, concentration in molarity and mean activity coefficient?From what i understand, it cannot be found without molality (m)

Scroll to see replies

Reply 1
Avatar for alow
alow
19
Original post by lucasleiva
may i know how to calculate the ionic activity of an ion, a+-, given the ionic strength, I, concentration in molarity and mean activity coefficient?From what i understand, it cannot be found without molality (m)


Take a look here: http://www.aqion.de/site/69
Reply 2
Avatar for lucasleiva
lucasleiva
OP
Original post by alow
Take a look here: http://www.aqion.de/site/69

hmmm i cant find my answer there?
Reply 3
Avatar for lucasleiva
lucasleiva
OP
is this formula correct?ionic activity, a+-= activity coefficient multiply with molarity (M)
Reply 4
Avatar for alow
alow
19
Original post by lucasleiva
hmmm i cant find my answer there?



Original post by lucasleiva
is this formula correct?ionic activity, a+-= activity coefficient multiply with molarity (M)


Are you sure you read what I posted?

There's also this which is the same thing but prettier: https://web.stanford.edu/~cgong/cee373/documents/CEE373Lecture03.pdf

Also what is a+-? Do you mean a±a^{\pm}?
Reply 5
Avatar for lucasleiva
lucasleiva
OP
Original post by alow
Are you sure you read what I posted?

There's also this which is the same thing but prettier: https://web.stanford.edu/~cgong/cee373/documents/CEE373Lecture03.pdf

Also what is a+-? Do you mean a±a^{\pm}?


a+- is mean ionic activity?
Reply 6
Avatar for alow
alow
19
Original post by lucasleiva
a+- is mean ionic activity?


Okay... so did you not read the first site I posted? Everything is explained there.
Reply 7
Avatar for lucasleiva
lucasleiva
OP
Original post by alow
Okay... so did you not read the first site I posted? Everything is explained there.


i did, and it is stated
ai = γi ci, so just multiply molarity with activity coefficientt?
Reply 8
Avatar for alow
alow
19
Original post by lucasleiva
i did, and it is stated
ai = γi ci, so just multiply molarity with activity coefficientt?


Well yeah... that's how you calculate activity. It's calculating γi\gamma_i where you have to consider Ionic strength.

Is this actually a question which has been given to you? What is the precise wording of the entire question as what you've posted does not make much sense as there are a multitude of answers using different models.
Reply 9
Avatar for lucasleiva
lucasleiva
OP
Original post by alow
Well yeah... that's how you calculate activity. It's calculating γi\gamma_i where you have to consider Ionic strength.

Is this actually a question which has been given to you? What is the precise wording of the entire question as what you've posted does not make much sense as there are a multitude of answers using different models.

the whole question is calculate the ionic strength, mean activity coefficient and the ionic activity of 0.0325M K4Fe(CN)6 at 298K
Reply 10
Avatar for alow
alow
19
Original post by lucasleiva
the whole question is calculate the ionic strength, mean activity coefficient and the ionic activity of 0.0325M K4Fe(CN)6 at 298K


So have you found any of those yet?
Reply 11
Avatar for lucasleiva
lucasleiva
OP
Original post by alow
So have you found any of those yet?


My answer is:
Ionic strength: 0.325
Mean activity coefficient: 0.06907Mean ionic activity: 0.0325 x 0.06907 = 0.00224
Am i right?
Reply 12
Avatar for alow
alow
19
Original post by lucasleiva
My answer is:
Ionic strength: 0.325
Mean activity coefficient: 0.06907Mean ionic activity: 0.0325 x 0.06907 = 0.00224
Am i right?


Your Ionic Strength is right. Which model did you use to find the activity coefficients?
Reply 13
Avatar for lucasleiva
lucasleiva
OP
Original post by alow
Your Ionic Strength is right. Which model did you use to find the activity coefficients?


Debye Huckel limited law?
Reply 14
Avatar for alow
alow
19
Original post by lucasleiva
Debye Huckel limited law?


If you look on this site: http://www.aqion.de/site/101 it shows that Debye-Huckel is only appropriate for I < 10-2.3M.
Reply 15
Avatar for lucasleiva
lucasleiva
OP
Original post by alow
If you look on this site: http://www.aqion.de/site/101 it shows that Debye-Huckel is only appropriate for I < 10-2.3M.


but the question did not provide me the constant values that can be used for the extended debye huckel limiting rule?
Reply 16
Avatar for alow
alow
19
Original post by lucasleiva
but the question did not provide me the constant values that can be used for the extended debye huckel limiting rule?


Extended Debye-Huckel is also not valid. You should really use the Davies model.

Is your solution aqueous?
Reply 17
Avatar for lucasleiva
lucasleiva
OP
Original post by alow
Extended Debye-Huckel is also not valid. You should really use the Davies model.

Is your solution aqueous?


the question just provdide 0.0325M solution of K4Fe(CN)6
Reply 18
Avatar for alow
alow
19
Original post by lucasleiva
the question just provdide 0.0325M solution of K4Fe(CN)6


I would assume it is aqueous then.
Reply 19
Avatar for lucasleiva
lucasleiva
OP
Original post by alow
I would assume it is aqueous then.


may i know is my method of calculating the mean ionic activity is right or wrong?i multiply the activity coefficient with the molarity (0.0325M)

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you