Question 1

Which of the following best describes the equilibrium shown in the first image (antibody + antigen ⇄ antibody-antigen complex)?

Accepted Answer

A reversible binding interaction characterized by an affinity constant $$K_{affinity}.$$

Question 2

Given the pH scale in the second image, what is the pH of a solution that is 100 times more acidic than pure water (pH 7)?

Accepted Answer

$$pH = 5$$

Question 3

Thymol blue is used as an acid-base indicator as shown in the third image. At which pH value would you expect the solution to be yellow?

Accepted Answer

$$pH = 5$$

Question 4

Which instrument shown in the fourth image is used to measure the pH of a solution with high precision?

Accepted Answer

A pH meter with a glass electrode

Question 5

A student titrates a weak acid with a strong base using the setup in the fifth image. What is the best method to determine the equivalence point?

Accepted Answer

Record the pH after each addition of base and plot the titration curve.

Question 6

Which glassware in the sixth and seventh images is best for preparing a solution of known volume and concentration?

Accepted Answer

Volumetric flask

Question 7

The buffer capacity graph (image 12) shows a peak at a certain pH. What does this peak represent?

Accepted Answer

The pH equal to the $$pK_a of $$the weak acid in the buffer.

Question 8

Which equation would you use to calculate the pH of a buffer solution containing a weak acid and its conjugate base?

Accepted Answer

$$pH = pK_a + \log \frac{[A^-]}{[HA]}$$

Question 9

A solution contains 0.001 mol/L HCl and 0.001 mol/L HNO$$_2. $$Which solution will have the lower pH and why?

Accepted Answer

HCl, because it is a strong acid and dissociates completely.

Question 10

Which of the following best describes a zwitterion, as seen in the amino acid structures?

Accepted Answer

A molecule with both positive and negative charges but an overall neutral charge.

Question 11

Given the structure of glutamic acid and its p$$K_a$$ values (p$$K_{a1} = 2.19$$, p$$K_{a2} = 4.25$$, p$$K_{a3} = 9.67$$), what is the isoelectric point ($$pI) of $$glutamic acid?

Accepted Answer

$$pI = \frac{2.19 + 4.25}{2} = 3.22$$

Question 12

Which type of antibody would be most appropriate for detecting a single, specific variant of a virus in a diagnostic test?

Accepted Answer

Monoclonal antibody

Question 13

In an agglutination assay for blood typing (see image), what is the principle behind the visible clumping?

Accepted Answer

Antibody-antigen complexes form large aggregates that scatter light.

Question 14

Which of the following best explains why sandwich assays (such as pregnancy tests) are more specific than single-antibody assays?

Accepted Answer

They use two antibodies that bind to different epitopes on the same antigen.

Question 15

If you want to prepare a buffer with pH = 5.00 using acetic acid ($$pK_a = 4.74) $$and sodium acetate, what ratio of $$[A^-]/[HA]$$ should you use?

Accepted Answer

$$[A^-]/[HA] = 10$$^{(5.00-4.74)}$$

Question 16

Which of the following statements about buffer solutions is correct?

Accepted Answer

Buffers are most effective when $$pH = pK_a of $$the weak acid.

Question 17

A solution contains 0.01 M acetic acid and 0.01 M sodium acetate. If 0.0005 moles of NaOH are added to 100 mL of this buffer, what will happen to the pH?

Accepted Answer

The pH will increase slightly, but the buffer will resist a large change.

Question 18

Which of the following best describes the relationship between $$pK_a$$ and acid strength?

Accepted Answer

A lower $$pK_a$$ value indicates a stronger acid.

Question 19

Which of the following is true about the fraction of dissociation ($$\alpha_d) $$for a weak acid as its concentration decreases?

Accepted Answer

The fraction of dissociation increases as concentration decreases.

Acid-Base and Antibody-Antigen Equilibria: Analytical Chemistry Study Notes

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