JEE Main On 08 April 2018 Question 23

Question: The predominant form of histamine present in human blood is $ \text{(p}{K_a},Histidine=6.0) $ [JEE Main Online 08-04-2018]

Options:

A)

B)

C)

D)

Show Answer

Answer:

Correct Answer: B

Solution:

  • Isoelectronic point $ =\frac{5.74+9.8}{2}=7.77 $ Histamine has two basic center which are Aliphatic amino group and imidazole ring. In blood, the aliphatic amino group (pKa = 9.4) will be exist whereas the second nitrogen of imidazole ring (pKa = 5.8) will not be protonated in blood which pH is 7.4. $ \text{pH=pKa+log}\frac{[\text{ Salt }]}{[\text{ Acid }]} $ $ 7\text{.4=}\underset{\begin{smallmatrix} \downarrow \\ \text{It should be high for balancing} \end{smallmatrix}}{\mathop{7\text{.77+log}\frac{[\text{ Salt }]}{[\text{ Acid }]}}}, $