titration and amino acids 9/10

Question 1

when pK_a= pH what does that mean?

Answer 1

base = acid

Question 2

How much NaH2PO4 would you have to add to water to get 1 liter of a pH 5.5 solution?

pK_a=6.86

Answer 2

pH = pKa + log b/a

5.5 = 6.86 + log (10-5.5/a)

a = 10-5.5/ 10-1.36 = 7.24x10-5 mole of acid form

Total added is acid + base:
7.24x10-5 + 10-5.5 = 7.56x10-5 moles

pH 5.5 is 1.36 pH units below pKa

So there is 23x more acid than base at pH 5.5

Question 3

what does alpha amino acid mean?

Answer 3

they consist of an amino, carboxyl, hydrogen and side chain attached to an alpha carbon

Question 4

what do pK₁, pK₂, and pK_R represent?

Answer 4

pK₁ = carboxyl group

pK₂ = alpha amino group

pK_R = R group

Question 5

how many titratable groups can amino acids have?

Answer 5

2 or 3

Question 6

amino acids exist in differently charged forms at

Answer 6

different pH

Question 7

zwitterion form

Answer 7

neutral pH able to accept or donate protons

Question 8

isoelectric pH

Answer 8

pH at which the average charge on an amino acid is 0; can be determined by tritration curve and known pK_a values for each group; average of the two pK values on either side of neutral charge form

Question 9

what is isoelectric focusing?

Answer 9

could be used to separate amino acids from each other but normally not the most convenient method for amino acids but used for separating mixtures of peptides or proteins

Question 10

ion exchange chromatography

Answer 10

often used to separate a mixture of amino acids and identify the individual amino acids

Question 11

how does the change in pH change the amino acid

Answer 11

the charge will change based on whether the pH is low or high