a. Hºsoln (standard state) of KCl is +17.2 kJ/mole. What is Sºsurr ? If the mola

Question

a. Hºsoln (standard state) of KCl is +17.2 kJ/mole. What is Sºsurr ? If the molar solubility of KCl is 4.2 M, what does this tell you about the value and sign of Sºsys ?
b. If the solution is at pH=7, then what is the overall charge of a protein whose pI=9? a. Hºsoln (standard state) of KCl is +17.2 kJ/mole. What is Sºsurr ? If the molar solubility of KCl is 4.2 M, what does this tell you about the value and sign of Sºsys ?
b. If the solution is at pH=7, then what is the overall charge of a protein whose pI=9? a. Hºsoln (standard state) of KCl is +17.2 kJ/mole. What is Sºsurr ? If the molar solubility of KCl is 4.2 M, what does this tell you about the value and sign of Sºsys ?
b. If the solution is at pH=7, then what is the overall charge of a protein whose pI=9?

Explanation / Answer

(b)

At pI, the net charge on an amino acid is zero. At pH values above the pI, there is an overall negative charge, and at pH values below pI, the overall charge is positive.

This is because of the following Henderson Hasselbach relation:

pH = pKa + log(a/(1-a))

Here, 'a' is the degree of dissociation of the ionizable group

When pH is less than pKa, the group is fully protonated and hence carries a positive charge.

So when pI = 9, the protein will have a positive charge at pH = 7

Hope this helps !

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