Alanine, h2nch (ch3) co2h, has ka = 4.5  10-3 and kb = 7.4  10-5. which species has the highest concentration at a ph of 7.00 in h2o?

Question

Chemistry

Hazel Frank

13 September, 14:30

Alanine, h2nch (ch3) co2h, has ka = 4.5  10-3 and kb = 7.4  10-5. which species has the highest concentration at a ph of 7.00 in h2o?

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Marianna · Answer 1

Answer is: the highest concentration has ⁺H₃NCH (CH₃) CO₂⁻.

pKa (carboxylic group) = - log (4,5·10⁻³) = 2,35.

pKb (amino group) = - log (7,4·10⁻⁵) = 4,13.

pKa + pKb = 14.

pKa (amino group) = 14 - 4,13 = 9,87.

At pH = 7 carboxylic group lost proton (H⁺) and became COO⁻, amine is protoneted (NH₃⁺) in this pH value.