Dr.Bob,
Arrange these acids in terms of increasing acidity:
CH3COOH, NH3+CH2COOH, CH3CONHCH2COOH
According to my Chem textbook,NH3+CH2COOH has a low pKa value since both the COOH & NH3+ are protonated,so it is most acidic. CH3COOH is a weak acid, but I'm not sure about the N-acetylglycine.Dr.Bob said earlier that I had the order reversed,which means CH3COOH is most acidic among all three. Hope Dr.Bob can explain why my assumptions went wrong.
Thank you
First, can you tell me what NH3+CH2COOH is. I have no idea. Is this a way of writing NH3 + CH3COOH for ammonium acetate. CH2COOH isn't anything is it?
Ok,that NH3+CH2COOH is obtained when 1 mol of glycine is added with a strong acid,which results in both amino & carboxyl groups to be fully protonated.
See my later post to your explanation. However, I think you get the amino group protonated; the carboxyl group is already fully protonated isn't it?
To determine the order of acidity for the given acids, we need to consider the factors that contribute to acid strength. These factors include the stability of the conjugate base, electronegativity, and the ability to delocalize charge or stabilize negative charge.
Let's analyze each of the given acids to determine their acidity:
1. CH3COOH: This is acetic acid, a weak acid. The carboxylic acid group (COOH) can release a proton (H+) but is not as stable in its conjugate base form (CH3COO-). The electronegativity and delocalization of charge are lower, which makes it a weaker acid compared to the other two.
2. NH3+CH2COOH: This is an amino acid called glycine. It has an amino group (NH3+) and a carboxylic acid group (COOH). The amino group has a positive charge, which stabilizes the conjugate base (NH2CH2COO-). This positive charge increases the acidity since it can easily lose a proton. Therefore, this acid is stronger than acetic acid.
3. CH3CONHCH2COOH: This is N-acetylglycine, which also acts as an amino acid with additional functional groups. The presence of an amide group (CONH) increases the stability of the conjugate base (CH3CONHCH2COO-) compared to the carboxylic acid group alone. This makes it more acidic than acetic acid but less acidic than NH3+CH2COOH.
Therefore, the correct order in terms of increasing acidity is:
CH3COOH < CH3CONHCH2COOH < NH3+CH2COOH
It's important to note that acidity is a complex concept influenced by multiple factors, and it can sometimes be challenging to determine the absolute acidity of compounds without experimental data or more detailed calculations.