CH228H Unit 5 Reassessment

CH 228H Unit 5 Reassessment

 

Instructions:

 

1. Hand draw/write your answers to each problem on white or lined paper.
2. Make sure your answers are legible.
3. Once you have completed the reassessment, return your work by email.
4. The reassessment problems start on the next page.

 

Resources for the Unit 5 Reassessment

You may use any of your Course Materials while you are completing the reassessment

 

 

Criterion 1: Use definitions to correctly identify and predict acids, bases, and conjugate acid-base pairs in acid-base reactions

 

 

 

Problem 1

Amino acids are the building blocks of the proteins in your body. As the name implies amino acids contain both an acidic functional group (carboxylic acid) and a basic functional group (amine). The structure of the amino acid asparagine is shown below.

 

 

O

 

H2N

 

NH2

OH

 

O

 

asparagine

 

Draw in the products of the following 2 reactions. Label the acid/base on each side of the reactions and connect conjugate acid/base pairs.

 

a.	O         NH2 +                                 H N                           OH                     +     H3O 2 O
b.	O          NH2 OH                               –                              H2N                                               +     HO O

 

Problem 2

Finish the equation below for the dissociation of asparagine in water where asparagine is acting as a weak acid. Clearly show the structure of the product(s).

 

 

O

 

H2N

 

NH2

OH

 

O

 

 

+     H2O

 

 

Problem 3

Finish the equation below for the reaction of asparagine with water where asparagine is acting as a weak base. Clearly show the structure of the product(s).

 

 

O

 

H2N

 

NH2

OH

 

O

 

 

+     H2O

 

 

Criterion 2: Identify polar acidic, polar basic, polar neutral, and nonpolar functional groups in organic structures

 

 

 

Problem 4

For each molecule given below:

1. 1. redraw each one
   2. label and identify all functional groups in each one
   3. classify each functional group as: polar acidic, polar basic, polar neutral or nonpolar.

 

Molecule I	Molecule II	Molecule III	Molecule IV	Molecule V
H H2N    C     CO2H H2C   N N   H His	H   H2N     C     CO2H HC     OH CH3 Thr	H H2N C CO2H CH3 Ala	HO            OH     HO                                  O O HO   Vitamin C	OH       N H   Pseudoephedrine (decongestant)

 

 

Criterion 3: Define Ka and pKa and use values to predict the relative strength of acids

 

 

 

 

Problem 5

Write the expression for the Ka of asparagine. The structure of asparagine is given in Criterion 1 Problem #1. Remember to use the acid dissociation reaction in water when determining the Ka expression. Do not use condensed structures. Clearly show which structure is in the numerator and the denominator.

 

Problem 6

Two weak acids are given below along with the Ka for each.

 

Acid	Ka
O   Carbonic Acid, HO        OH	4.3 x 10-7
O   Acetic Acid,        OH	1.8 x 10-5

 

1. Write the acid dissociation reaction for BOTH of these weak acids. Remember this means the reaction with water.
2. Label the acid, base, conjugate acid and conjugate base and connect conjugate acid/base pairs.
3. Write the Ka expression for both weak acids.
4. Which one of these 2 acids is the weaker one?

 

 

Criterion 4: Accurately articulate how a buffer is created, how to predict and control the pH of a buffer, how buffers work to maintain pH in a narrow range, and the physiological importance of buffers in the body

 

 

Problem 7

Consider the following reaction.

 

HPO4?2      +     H2O                                            PO4?3         +       H3O+

 

Ka  =            4.72 x 10-11

 

 

1. Label the acid/base on each side of the equation. Connect the conjugate acid/base pairs.

 

1. How do the formulas for a weak acid and its conjugate base differ?

 

1. Explain why this system represents a buffer.

 

1. What is the purpose of this buffer system?

 

1. What compounds would you add to water to make this buffer?

 

1. What is the initial pH of this buffer system?

 

1. What would happen to the pH of this buffer if a small amount of strong acid was released into the blood stream?

 

Problem 8

Describe the components of a buffer, how a buffer is made, how it works and what behavior is expected for buffers under the conditions of either added base or added acid.