8.7 pH and pKa

Multiple Choice

The equilibrium constant for the reaction HA + H2O ⇌ H3O+ + A- is represented by the formula K_a = [H+][A-]/[HA]. What does this formula help to determine?

• The strength of the acid

• The color of the solution

• The temperature of the reaction

• The pressure of the system

Multiple Choice

What is the Henderson-Hasselbalch equation used for?

• Calculating the pH of a solution

• Determining the equivalence point

• Measuring the concentration of a base

• Identifying the midpoint of a titration

Open Ended

Explain the significance of the midpoint in the relationship between pH and pKa.

Multiple Choice

If pH < pKa, what can be inferred about the concentration of acid and base?

• [acid] > [base]

• [acid] = [base]

• [acid] < [base]

• [acid] is negligible

Fill in the Blank

Knowing pKa, we can predict ___ relationships at any pH.

Multiple Choice

According to Le Chatelier's Principle, what happens when the pH is lowered?

• Increase in [H3O+] and favoring of reverse reaction

• Decrease in [H3O+] and favoring of forward reaction

• Increase in [A-] and favoring of forward reaction

• Decrease in [HA] and favoring of reverse reaction

Multiple Choice

What is the role of an acid-base indicator in a titration?

• To measure the pH directly

• To change color at the equivalence point

• To neutralize the acid

• To increase the reaction rate

Multiple Choice

What is the role of methyl red as an indicator in acid-base reactions?

• It changes color at a specific pH range

• It remains colorless throughout

• It reacts with acids only

• It reacts with bases only

Open Ended

Explain the importance of choosing the correct indicator for a particular reaction.

Multiple Choice

Which statement is true about methyl red based on the pH scale?

• It is red at low pH and yellow at high pH

• It is yellow at low pH and red at high pH

• It is colorless at all pH levels

• It changes color randomly

Fill in the Blank

In a mixture, if one color is ten times stronger than the other, our eyes will only detect the ___ color.

Multiple Choice

What is the color change range for methyl red on the pH scale?

• Red to yellow

• Yellow to blue

• Blue to red

• Colorless to red

Open Ended

Would the protonated or the deprotonated form of alizarin red s be red? Explain your reasoning.

Open Ended

Which species is present in a greater amount, the protonated HNO2 or the deprotonated NO2-?

Fill in the Blank

A buffered solution resists changes to its pH when small amounts of ___ are added.

Multiple Choice

What is the equilibrium constant expression for the reaction HA(aq) + H2O(l) ⇌ H3O+(aq) + A−(aq)?

• K_a = [H+][A−]/[HA]

• K_a = [H3O+][A−]/[HA]

• K_a = [HA][H2O]/[H3O+][A−]

• K_a = [H+][HA]/[A−]

Open Ended

What is the relationship between the predominant form of a weak acid or base in solution at a given pH and the pK_a of the conjugate acid or the pK_b of the conjugate base?