Chem 153A - Midterm 1 Exam With Complete Solutions 100%
2025/2026
Instructions (please read carefully)
1. The exam consists of 6 questions (9 pages total)
2. Pen is preferred but if you use a pencil you MUST write dark
3. Take the time to write your name and ID on EVERY page (points will be deducted
otherwise!)
4. Do NOT write on the back of any page of the exam as we don’t scan the backs of pages.
If you cannot fit your answer in the provided space, write your answer on Page 8.
5. If you are in need of assistance, please raise your hand quietly. Do your best!
6. The only resources you are allowed are your brain, a writing utensil, and a calculator.
Usage of any other resource will result in your test being invalidated.
1
This study source was downloaded by 100000902164626 from CourseHero.com on 12-14-2025 11:11:34 GMT -06:00
https://www.coursehero.com/file/245937734/Chem-153A-Midterm-1-solutionspdf/
, 1. Amino acids and oligopeptides (15+1 pts)
a. You have a solution containing the following
species at the stated concentrations. at 0.03 M at 0.12 M
i. (2 pts) Is this a buffer system? Why or
why not?
buffer system because: the ratio between
yes no conjugate acid/base is less than 10:1 (or 1:10) OR
the pH of the solution is within one unit of the pKa
ii. (3 pts) What pH is this solution at? (show your work!)
pH = 9.5 + log(0.12/0.03) pH = 10.1
b. Consider the oligopeptide H-A-I-R
i. (5 pts) Draw this peptide at physiological conditions (pH = 7.4)
ii. (2 pts) What is the charge of the predominant form of H-A-I-R at a
pH of 4?
-2 -1 0 +1 +2
iii. (3 pts) Calculate the isoelectric point of this peptide (show work!)
pI = (8.5 + 12.5)/2 pI = 10.5
iv. (+1 serious bonus) What class/family of proteins (that we’ve
discussed in lecture) makes up the structure of human hair?
type of protein fibrous
2
This study source was downloaded by 100000902164626 from CourseHero.com on 12-14-2025 11:11:34 GMT -06:00
https://www.coursehero.com/file/245937734/Chem-153A-Midterm-1-solutionspdf/
2025/2026
Instructions (please read carefully)
1. The exam consists of 6 questions (9 pages total)
2. Pen is preferred but if you use a pencil you MUST write dark
3. Take the time to write your name and ID on EVERY page (points will be deducted
otherwise!)
4. Do NOT write on the back of any page of the exam as we don’t scan the backs of pages.
If you cannot fit your answer in the provided space, write your answer on Page 8.
5. If you are in need of assistance, please raise your hand quietly. Do your best!
6. The only resources you are allowed are your brain, a writing utensil, and a calculator.
Usage of any other resource will result in your test being invalidated.
1
This study source was downloaded by 100000902164626 from CourseHero.com on 12-14-2025 11:11:34 GMT -06:00
https://www.coursehero.com/file/245937734/Chem-153A-Midterm-1-solutionspdf/
, 1. Amino acids and oligopeptides (15+1 pts)
a. You have a solution containing the following
species at the stated concentrations. at 0.03 M at 0.12 M
i. (2 pts) Is this a buffer system? Why or
why not?
buffer system because: the ratio between
yes no conjugate acid/base is less than 10:1 (or 1:10) OR
the pH of the solution is within one unit of the pKa
ii. (3 pts) What pH is this solution at? (show your work!)
pH = 9.5 + log(0.12/0.03) pH = 10.1
b. Consider the oligopeptide H-A-I-R
i. (5 pts) Draw this peptide at physiological conditions (pH = 7.4)
ii. (2 pts) What is the charge of the predominant form of H-A-I-R at a
pH of 4?
-2 -1 0 +1 +2
iii. (3 pts) Calculate the isoelectric point of this peptide (show work!)
pI = (8.5 + 12.5)/2 pI = 10.5
iv. (+1 serious bonus) What class/family of proteins (that we’ve
discussed in lecture) makes up the structure of human hair?
type of protein fibrous
2
This study source was downloaded by 100000902164626 from CourseHero.com on 12-14-2025 11:11:34 GMT -06:00
https://www.coursehero.com/file/245937734/Chem-153A-Midterm-1-solutionspdf/
