Problem Set 1: Buffers and Amino Acids

Opened: Saturday, 11 February 2023, 12:00 AM
Due: Saturday, 18 February 2023, 7:00 PM
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General Instructions

  1. This is a group activity. 
  2. Answer the problems shown below use the previously given pKa table as reference.
  3. Submit your answers in pdf/jpg formats only following naming, Chem40_PS1_<Section>_<Group No.>
  4. One submission per group is enough. 

Problems

  1. What is the pH of a buffer prepared by adding 6.4g of NaOAc and 2.5ml HOAc to make 100ml of a buffer? The pKa of HOAc is 4.7. MW of NaOAC is 82 g/mol, while the MW of HOAc is 60 g/mol. Density of HOAc is 1.049. (OAc=acetate, HOAc=acetic acid)
  2. What is the pH of 0.1 M HCl? What is the pH of the same concentration of HOAc, Ka = 1.8\times10^{-5}?
  3. If you have 100 ml of a 0.10 M Tris buffer at pH 8.3 and you add 3.0 ml of 1M HCl, what will be the new pH of the solution? (Tris pKa= 8.3)
  4. Name an amino acid in which the R group contains the following:
    –A hydroxyl group
    –An amide group
    –An acid group
    –A branched side chain
    –An aromatic ring
  5. Identify the nonpolar amino acids and the acidic amino acids in the following peptide: Glu-Thr-Val-Asp-Ile-Ser-Ala

  6. Draw the structures of the following amino acids, indicating the charged form that exists at pH 4 and 10, respectively: H, N, W, P, Y

  7. Sketch the titration curve for the amino acid cysteine and indicate the pKa values for all titratable groups. Also indicate the pH at which the zwitterion form predominates.