Acid-Base Equilibria - Drug pH Calculations

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Questions and Answers

What is the concentration of hydroxide ions, [OH-], in a 100.0 mL solution of 0.1000 M NaOH?

1.000 x 10^-4 M

1.000 x 10^-1 M (correct)

1.000 x 10^-3 M

1.000 x 10^-2 M

If the hydroxide ion concentration [OH-] is 1.000 x 10^-1 M, what is the concentration of hydronium ions, [H3O+]?

1.000 x 10^-11 M

1.000 x 10^-12 M

1.000 x 10^-13 M (correct)

1.000 x 10^-14 M

What is the pH of a 0.1000 M NaOH solution?

11.0000

14.0000

12.0000

13.0000 (correct)

When calculating pH before reaching the equivalence point in a titration, what needs to be considered?

The concentrations and volumes of both the titrant and analyte Signup and view all the answers

Which statement correctly explains how to calculate the pH after mixing NaOH with an acid before the equivalence point?

Use the total volume and the moles of NaOH to determine the concentration of hydroxide ions. Signup and view all the answers

How does the sharpness of the endpoint in titration change with varying pH levels?

The endpoint becomes less sharp as pH decreases. Signup and view all the answers

What can be inferred about complex formation at lower pH levels?

Complex formation is less complete at lower pH levels. Signup and view all the answers

In the context of titration, what role does the pH play in the reaction with EDTA?

Lower pH levels lead to reduced complexation efficiency. Signup and view all the answers

Which statement best describes the relationship between pH and the completeness of the complex formation?

Higher pH leads to more complete complex formation. Signup and view all the answers

What is the primary effect of reducing pH on the titration curve of Ca2+ with EDTA?

The titration curve becomes less defined. Signup and view all the answers

What determines the hydrogen ion concentration in solutions of salts formed from strong acids and bases?

Dissociation of water only Signup and view all the answers

What is the pH of a neutral solution formed with salts of strong acids and bases?

7 Signup and view all the answers

Which ions are mentioned as not reacting with water?

K+ and Cl- Signup and view all the answers

If a solution contains only a strong acid and a strong base, what is the expected concentration of hydrogen ions?

10^-7 M Signup and view all the answers

In a salt solution derived from strong acid and strong base, what can be inferred about the acidity or basicity of the solution?

The solution is neutral Signup and view all the answers

What occurs to the Ag+ ions after the equivalence point in a titration?

There is excess Ag+ in solution. Signup and view all the answers

What is the effect of the adsorbed charge on the surface of the crystal during the reaction?

It induces a partial negative charge on the crystal surface. Signup and view all the answers

How does the negative charge on the surface of the crystal affect interaction with Ag+ ions?

It repels Ag+ ions due to like charges. Signup and view all the answers

What phenomenon can result from the presence of excess Ag+ ions in a solution?

Increased crystallization of Ag salts. Signup and view all the answers

What is the significance of reaching the equivalence point in a titration involving Ag+ ions?

It shows that no excess reactants remain. Signup and view all the answers

What occurs at the equivalence point during a titration involving A-?

A- hydrolyzes as a weak base. Signup and view all the answers

What dominates the solution beyond the equivalence point in a titration?

Excess OH- ions from the base. Signup and view all the answers

How is a weak base treated during a titration process compared to a titration involving a weak acid?

It begins with base and ends with acid. Signup and view all the answers

What is the primary characteristic of A- at the equivalence point in terms of its acid-base behavior?

A weak base that hydrolyzes in an aqueous solution. Signup and view all the answers

Which statement accurately describes the behavior of excess OH- beyond the equivalence point?

It leads to an increase in the solution's pH. Signup and view all the answers

What is the primary purpose of using a titrant standard solution in a titration?

To determine the concentration of an unknown solution Signup and view all the answers

Which statement correctly describes the titration curve of a weakly basic drug titrated with a strong acid?

It will show a rapid drop in pH near the equivalence point. Signup and view all the answers

When constructing titration curves for polyfunctional acidic/bases, which calculation is primarily needed?

Determining the pKa values of each functional group Signup and view all the answers

In the titration of weak acidic drugs, what factor most significantly affects the curvature of the titration graph?

The concentration of the weak acid compared to the titrant Signup and view all the answers

Which equation is most relevant when calculating the results of a titration involving weakly basic drugs?

$K_b = \frac{[OH^-][HB^+]}{[B]}$ Signup and view all the answers

Study Notes

Acid-Base Equilibria - ILO's

Calculate the pH scale of hydrogen ion concentration
Evaluate pH values of salts of simple weak acidic and basic drugs
Use the Henderson-Hasselbalch equation to estimate the pH of a buffer solution and find the equilibrium pH in acid-base reactions of weak drugs
Recognize the concept of buffering capacity as a quantitative measure of resistance to pH change upon the addition of H+ or OH- ions
Explain polyprotic acidic and basic drugs and their salts
Calculate the pH of the solution of a polyprotic acidic and basic drugs
Construct fractions of polyprotic species as a function of pH

Acidic/Basic Drugs - pKa Values

Acetyl salicylic acid (Acid) - pKa 3.49
Benzyl penicillin (Acid) - pKa 2.76
Ethosunamide (Acid) - pKa 9.3
Chlorpropamide (Acid) - pKa 4.8
Sulfadrazine (Acid) - pKa 6.48
Dephenghydantoin (Acid) - pKa 8.3
Atropine (Base) - pKa 9.65
Amphetamine (Base) - pKa 9.8
Lignocaine (Base) - pKa 7.9
Procaine (Base) - pKa 8.8
Tetracycline (Base) - pKa 3.3, 7.8, 9.7

Acid-Base Theories

Arrhenius Theory:
- Acid: substance that ionizes in water to produce H+ ions increasing H3O+ concentration
- Base: substance that ionizes in water to produce OH- ions
- Limitation: doesn't explain acids/bases in non-aqueous solutions
Brønsted-Lowry Theory:
- Acid: proton donor
- Base: proton acceptor
- Conjugate acid-base pairs involve the transfer of a proton
- Reactions involve acid donating a proton to a base

Lewis Acids and Bases

Lewis Acid: electron pair acceptor
Lewis Base: electron pair donor

Amphiprotic Solvents and Solutes

Amphiprotic Solvents: exhibit both acidic and basic properties (e.g. water, methanol, ethanol, glacial acetic acid)
Amphiprotic Solutes: act as both acids and bases (e.g. HCO3⁻, HPO₄²⁻)

pH Scale

pH = -log[H+]
pAnything = -log(Anything)
pKw = -logKw at 25°C = 14.00
Kw = [H+][OH-]
pKw = pH + pOH = 14
Blood pH (at 37°C) is 7.35-7.45 (slightly basic).

Salts of Strong Acids and Bases

The pH of salts of strong acids or bases remains constant (pH=7).
Ions of these salts do not react with water.

Weak Acids and Bases

A weak acid/base partially dissociates in water.
Equilibrium constant is small
Amount dissociated is negligible compared to the original concentration.

pH Calculations - Examples

Examples demonstrate calculations for strong and weak acids/bases using equilibrium expressions.
Calculations consider the contribution of water dissociation to the overall H+ concentration, and use the assumption that x is small
Examples demonstrate how to find pOH and then pH using equilibrium constants.

Salts of Weak Acids and Bases

Salts of weak acids and bases are not neutral.
Conjugate bases of weak acids can hydrolyze in water to increase the OH⁻ concentration
Salts and bases influence pH

Buffer Solutions

A buffer resists changes in pH upon addition of small amounts of acid or base.
Buffer solutions contain a weak acid and its conjugate base, or a weak base and its conjugate acid
The Henderson-Hasselbalch equation relates pH to the pKa and concentrations of the weak acid and conjugate base

Polyprotic Acids and Their Salts

Polyprotic acids can donate more than one proton.
Stepwise dissociation; each step has its own equilibrium constant
Dissociation constants become progressively smaller as a result of the increasing negative charge.

Acid-Base Titrations

Calculate titration curves.
Recognize acid-base color indicators.
Calculate titration curves with weakly acidic drugs vs. strong base.
Calculate titration curves with weakly basic drugs vs. strong acid.
Calculate equations for weak acidic/basic drugs' titrations.
Calculate & construct polyfunctional acidic/basic titration curves (including drugs).

Titration

A standard solution with known concentration (titrant) is used to determine the concentration of an unknown solution (analyte).
The reaction occurring is a neutralization reaction.
Acidimetry/Alkalimetry
The quantitative determination of basic/acidic drugs respectively

Volumetric Analysis - Acid-Base Titrations - Additional Topics

Calculate the pH before a titration begins.
Explain how to find pH during a titration before reaching the equivalence point
Determine pH at equivalence point
How to find pH after equivalence point

Titration Curves for Strong Acids and Bases

Strong acids and bases completely dissociate
Stoichiometric ratio of the acid-base reaction is considered.
Only one equilibrium is considered in the calculations (ion product constant, Kw)

Titration Curves for Weak Acids/Weak Bases

Weak acids and bases partially dissociate.
Henderson-Hasselbalch equation is used in the buffer region to calculate pH.
Consider hydrolysis at the equivalence point.

Polyfunctional Acids/Bases

Polyprotic acids/bases have multiple ionizable groups.
Equivalence points may occur at multiple pH values for polyprotic acids/bases.

Amino Acids

Amino acids are polyprotic.
Zwitterions.

Appendix - Aqueous Titrations from USP

Provides specific procedures for direct and indirect titrations of different substances, including quantities, indicators and calculations using standardized solutions. Note: these are USP specific titration methods.

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Description

This quiz covers the fundamental concepts of acid-base equilibria, including the calculation of pH values for various acidic and basic drugs. It explores the use of the Henderson-Hasselbalch equation, buffering capacity, and polyprotic species. Test your knowledge on calculating pH and understanding drug properties related to acidity and basicity.