1) For the following question, assume the pKa of the alpha-carboxyl group = 2.0.
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Question
1) For the following question, assume the pKa of the alpha-carboxyl group = 2.0.
What would be the charge of the alpha-carboxyl group of glycine at pH 7?
2) For the following question, assume the pKa of the alpha-carboxyl group = 2.0. What would be COOH:COO- ratio of the alpha-carboxyl group of glycine at pH 3?
3) For the following question, assume the pKa of the alpha-carboxyl group = 2.0. What would be the COOH:COO-ratio of the alpha-carboxyl group of glycine at pH 2?
4) For the following question, assume the pKa of the alpha-amino group = 10.0. What would be charge of the alpha-amino group of glycine at pH 12?
5) For the following question, assume the pKa of the alpha-amino group = 10.0. What would be the NH3+:NH2 ratio of the alpha-amino group of glycine at pH 9?
6) For the following question, assume the pKa of the alpha-amino group = 10.0. What would be charge of the alpha-amino group of glycine at pH 10?
7) What would be the charge of the imidazole side chain of histidine at pH 7? Assume the pKa of the side chain is 6.0.
8) Assume the pKa of the alpha-carboxyl group = 2.0 and the pKa of the alpha-amino group = 10.0. What would be the net charge of glycine at pH 6?
9) Assume the pKa of the alpha-carboxyl group = 2.0 and the pKa of the alpha-amino group = 10.0. What would be the net charge of glycine at pH 3?
10) Assume the pKa of the alpha-carboxyl group = 2.0 and the pKa of the alpha-amino group = 10.0. What would be the net charge of glycine at pH 9?
11) Assume the pKa of the alpha-carboxyl group = 2.0 and the pKa of the alpha-amino group = 10.0. What would be the net charge of aspartic acid at pH 9? Assume the pKa of the carboxyl side chain is 4.0.
12) Assume the pKa of the alpha-carboxyl group = 2.0 and the pKa of the alpha-amino group = 10.0. What would be the net charge of histidine at pH 3? Assume the pKa of the side chain is 6.0.
Explanation / Answer
by using the formula
pH = pKa - log [salt]/[acid]
we can apply ths to get the ans of all the parts
1] 7-2= -log [salt]/[acid]= 10^-5 = [salt ]/[acid ]
2]3-2= -log [salt]/[acid]= 10^-1= [salt ]/[acid ]
3] 2-2= -log [salt]/[acid]= 1 = salt = acid
4]as the pka of the compound is 10 and to us it is provided 12 so it would be a rather basic medium and the amino acid would lose the H+ from it and will remain + charged species
5]9-10 =-log [salt]/[base] = 10^1 =[salt]/[base]
6]at ph=10 the amino compound would be neutral and will not be attracted towards any of the cathode or the anode
7] the charge would be +ve as the medium is basic for the amino acid
8]the net pka of the compound is =10+2/2 =6 so at pH =6 the compound would be neutral
9]the net pka of the compound is = 10+2/2 =6 so at pH =6 the compound will be negatively charged at ph =3 as it will be an acidic medium for the compound
10]the net pka of the compound is =10+2/2 =6 so at pH =6 the compound will be +vely charged as the soln is basic at ph =9
11]for two carboxyl group yhge pka of the compound is =4+2 /2 =3 , so at pH =9 the comp will be +vly charged
12] for two ammino group the pka = 10+6 /2 =8 so at pH =3 the compound will behave negatively as the soln will behave negatively .......
the main concept is that we have to use the equation to find the pK a of the compound and than compute it to the given pH at the left side of the pKa that is less than the pka the soln behave acidic and to the right the soln behaves basically so the compound will remain negatively ..........
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