Lab 3: pH, Buffers, and Acid-Base Reactions

Acid

Substance donating hydrogen ions in water.

Base

Substance releasing hydroxide or absorbing hydrogen ions.

HCl

Strong acid donating protons in water.

Water (H2O)

Amphoteric substance acting as acid or base.

Conjugate Base

Species formed after an acid donates a proton.

Conjugate Acid

Species formed after a base accepts a proton.

Acid Dissociation Constant (Ka)

Equilibrium constant for acid ionization.

Strong Acid

Completely dissociates in solution, e.g., HCl. Acid with large Ka, equilibrium shifts right.

- Gastric Secretions

Weak Acid

Acid with small Ka, equilibrium shifts left. Partially dissociates in solution, fewer H+ ions.

- lemon juice: pH 2

Auto-ionization of Water

Water dissociating into H3O+ and OH-.

Dissociation Constant of Water (Kw)

Product of concentrations of H3O+ and OH-.

pH Scale

Logarithmic scale measuring hydrogen ion concentration.

pH Formula

pH = -log10[H+].

Neutral pH

pH of 7, equal concentrations of H+ and OH-.

pH 0

Indicates 1 M concentration of H+ ions.

pH 14

Indicates very low concentration of H+ ions.

Equilibrium Expression

[H+][OH-] = 1 x 10^-14 M.

Organic Acids

Typically weak acids found in biological systems.

Hydrogen Ion Concentration

Measured in molarity, affects pH value.

pH Decrease

Increased [H+] relative to [OH-].

pH Increase

Decreased [H+] relative to [OH-].

Dissociation

Process of an acid breaking into ions.

Ka

Equilibrium constant for weak acid dissociation.

pKa

Negative logarithm of the acid dissociation constant.

Henderson-Hasselbalch Equation

pH = pKa + log10([A-]/[HA]).

Buffer

Solution that resists pH changes upon acid/base addition.

Buffer Pair

Combination of weak acid and its conjugate base.

Acetic Acid

Common weak organic acid, CH3COOH. Used in buffer solutions.

Acetate

Conjugate base of acetic acid, CH3COO-.

Equilibrium

State where reactants and products remain constant.

Ionization

Process of forming ions from molecules.

Buffer Capacity

Amount of acid/base a buffer can neutralize.

pH Regulation

Maintaining constant H+ concentration in cells.

Enzyme Inactivation

Loss of enzyme function due to pH extremes.

HI

Hydroiodic acid, a strong acid indicator.

H+

Proton that influences acid-base balance.

OH-

Hydroxide ion that raises pH level.

pH Meter

Device for accurate pH measurement using electrodes.

Electrometric Method

Technique using voltage difference to measure pH.

Thymol Blue

Dibasic acid indicator, changes color at pH 1.2-9.6.

Brom Phenol Blue

Indicator changing from yellow (pH 3.0) to blue (pH 4.6).

Brom Cresol Green

Indicator changing from yellow (pH 4.0) to blue (pH 5.6).

Methyl Red

Indicator changing from red (pH 4.4) to yellow (pH 6.0).

Chlor Phenol Red

Indicator changing from yellow (pH 4.8) to red/purple (pH 6.0).

Brom Cresol Purple

Indicator changing from yellow (pH 5.2) to blue/purple (pH 6.8).

Brom Thymol Blue

Indicator changing from yellow (pH 6.0) to blue (pH 7.6).

Neutral Red

Indicator changing from red (pH 6.8) to orange (pH 8.0).

Phenol Red

Indicator changing from yellow/orange (pH 6.8) to red/pink (pH 8.4).

Cresol Red

Indicator changing from pink/orange (pH 7.2) to red/purple (pH 8.8).

Phenolphthalein

Indicator changing from colorless (pH 8.3) to red/pink (pH 10.0).

Buffer System

Solution that resists pH changes upon acid/base addition.

Hydrochloric acid solution used for titration.

0.1 M HCl

Sodium hydroxide solution used for titration.

0.1 M NaOH

In what increments should either acid/base be added to the water/buffer at a time?

5 drop increments

HAc

Acetic acid, a weak acid in solutions.

NaAc

Sodium acetate, a conjugate base of acetic acid.

Acid precipitation

Rain or snow with pH lower than 5.6.

Carbonic acid (H₂CO₃)

Weak acid formed from CO2 and water.

Natural acidity level of rainwater.

pH 5.8

SO2

Sulfur dioxide, contributes to acid rain formation.

Nitrogen oxides

Gases that form nitric acid in rain.

Environmental degradation, Acid rain

Damage to ecosystems from acid precipitation.

Acid rain - pH: 2.4

Buffering capacity

Ability to neutralize acidity.

Limestone soils

Soils that can buffer acid rain effects.

Acid-base response

Change in pH upon adding acid or base.

pH

Measure of hydrogen ion concentration in solution.

pH Indicator

Substance that changes color at specific pH.

Titration

Technique to determine concentration of a solution.

Sodium Acetate

Salt that acts as a buffer component.

NaOH

Strong base, fully dissociates in water.

Buffer Saturation

Point where buffer can no longer maintain pH.

pH Curve

Graph showing pH changes during titration.

pH of Water

Neutral pH is typically 7.

pH of AcH-NaAc

Buffer solution maintains pH around 4.76.

Acidic Solution

Solution with pH less than 7.

Basic Solution

Solution with pH greater than 7.