1.

If K_(a_1) and K_(a_2)are the ionisation constant of H_3overset+NCHRCOOH and H_2NCHRCOO^(-), respectively the pH of the solution at the isoelectric point is

Answer»

`PH=(pK_(a_1)+pK_(a_2))`
`pH=(ppK_(a_1)-pK_(a_2))^(1/2)`
`pH=(pK_(a_1)+pK_(a_2))^(1/2)`
`pH=(ppK_(a_1)+pK_(a_2))^(2)`

Solution :At a given pH, the species of AMINO acid EXISTS in equilibrium
`underset"Low pH"(H_3overset+N-undersetundersetR|CH-COOH) underset(H^+)overset(OH^-)hArr underset"Intermediate pH"(H_3overset+N-undersetundersetR|CH-COO^-) underset(H^+)overset(OH^-)hArr underset"HighpH"(H_2NundersetundersetR|CHCOO^-)` with `K_(a_1)=([H_3Noverset+CH(R)COO^(-)][H^(+) ])/([H_3overset+NCH(R)COOH])`
`K_(a_2)=([H_2NCH(R)COO^(-)][H^+])/([H_3N^(+)CHRCOO^(-)])`
Thus, `K_(a_1)K_(a_2)=([H_2NCH(R)COO^(-)][H^+]^2)/([H_3N^(+)CH(R)COOH])`
As isoelectric point, `[H_2NCH(R)COO^(-)]=[H_3N^(+)CH(R)COOH]`
Thus, `K_(a_1)K_(a_2)=[H^(+)]^2 ` or pH=`[pK_(a_1) + pK_(a_2)]^(1//2)`


Discussion

No Comment Found

Related InterviewSolutions