In the last part of the 2nd image, it says that the concentration is 3/4 and 1/4

Question

In the last part of the 2nd image, it says that the concentration is 3/4 and 1/4.. I want to know where they get the 3/4 and the 1/4 from.

Draw a stick structure of the peptide R-I-S-K in the predominant form found at pH 7.0 - please show all atoms and bonds in your drawing, and label the relevant pKa values for each ignitable group. Calculate the isoelectric point (pI) for this peptide, and make it clear how you arrived at your answer. What will the total charge be for this peptide in a solution at pH 8.48? Please make sure that your final answer, and all associated calculations, are clear (circle final answer if necessary)! (note that it is OK to consider any group fully (de)protonated when it is >2.0 pH units from its pKa). Don't forget that you have scratch paper at the back of the test!

Explanation / Answer

we got

[NH2 / NH3+] = 3

so the ratio of [ NH2] / [NH3+] = 3

the reaction is given by

NH2 + H+ ----> NH3+

initally [NH2] , [Nh3+] are 1, 0

at equilibrium [ NH2] , [NH3+] are 1- x , x

so

[NH2] + [NH3] = 1- x+ x =1

so

[NH2] + [NH3+] = 1

so

3[NH3+] + [NH2 ] = 1

4 [ NH3+] = 1

[Nh3+] = 1/4

[NH2] = 1 - [NH3+]

[NH2] = 1 - 1/4

[NH2] = 3/4

Related Questions

Navigate

• Browse (All)
• Browse I
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.