Titration Curve

Memorization Hack 💡

Protonated: Has a proton! HA contains an H in the name! This is acidic, as more acidic substances contain more H+. 

Deprotonated: No proton, does not contain an H in the name. This is basic which can be remembered as it only has one letter. "Basic!"  

Notes:

A titration curve plots how the pH changes as more and more basic titrant. Since lower on the pH scale is acidic, the left side of the graph showcases [HA], and the right side is basic showing [A-]. 

Additionally, the equivalence point is the pKa of the substance. You will notice that there is a steep curve around this point, and this is because around the pKa, there is the highest buffering point. This is due to the addition of water, as acetic acid is donating H+ to the water, so the pH does not increase at the same rate. 

The pKa tells you when a substance will be protonated vs deprotonated. If the pH is below the pKa, it will be protonated as the environment is an acid and donates H+ to the molecule. Conversely, if the pH is greater than the pKa, it will be deprotonated as the environment is basic and acts as a stronger H+ acceptor. 

Deprotonated pH > pKa 

Protonated pH < pKa

Determining Charge 

The information above allows us to determine the charge of an amino acid. For instance, if the pKa is 4.7, it can be determined from the surrounding pH if it will be protonated or not. 

If the pH is 3, it will be protonated. 

If the pH is 7, it will be deprotonated. 

Each amino acid will either be positive, negative, or uncharged at each protonation state. 

This can be applied to molecules that contain multiple "chargeable groups". This process is easier when you have memorized the amino acids and their charges! In this case, you determine the charge of each group at a certain pH and add the charges together.