glycine properties

[TimeforDAT]

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Why does it take two equivalents of base to completely neutralize glycine? glycine is H2NCH2COOH

thanks.

 

[whoaaitzkyle]

Look at the titration curve of glycine:

Glycine is normally +NH3CH2COOH...the amino acid is fully protonated

As you titrate NaOH, the carboxyl groups will lose its proton. Since the amino acid acts as a buffer, the pH changes very slowly. At the point, you added 0.5 moles of NaOH and this is where +NH3CH2COOH = +NH3CH2COO-...aka pka1=pH (refer to Henderson Hasselbach equation). After you add 1 mole, you have 100% +NH3CH2COO- now.

Add a second mole of NaOH and at the half equivalence point you'll get deprotonation of +NH3CH2COO- =NH2CH2COO-. After adding the full 2 moles of NaOH you will have 100% NH2CH2COO-.

 

[TimeforDAT]

Look at the titration curve of glycine:

Glycine is normally +NH3CH2COOH...the amino acid is fully protonated

As you titrate NaOH, the carboxyl groups will lose its proton. Since the amino acid acts as a buffer, the pH changes very slowly. At the point, you added 0.5 moles of NaOH and this is where +NH3CH2COOH = +NH3CH2COO-...aka pka1=pH (refer to Henderson Hasselbach equation). After you add 1 mole, you have 100% +NH3CH2COO- now.

Add a second mole of NaOH and at the half equivalence point you'll get deprotonation of +NH3CH2COO- =NH2CH2COO-. After adding the full 2 moles of NaOH you will have 100% NH2CH2COO-.

cool thanks