Acids, Bases, and Proteins: GOB Chemistry Exam 4 Review Notes

Acids and Bases

Definitions

Acids and bases are fundamental concepts in chemistry, especially in biological and environmental systems. Their definitions are based on their behavior in water.

• Acids: Proton donors (release H+ in water)

• Bases: Proton acceptors (accept H+ or release OH- in water)

Recognizing Acids and Bases in Reactions

• Strong Acids and Bases: Completely ionize in water.

  • Strong acids: HCl, HBr, HI, HNO3, H2SO4, HClO4

  • Strong bases: LiOH, NaOH, KOH, Ca(OH)2

Neutralization and Balancing Reactions

Acids and bases react to give H2O and a salt. Always balance the equation:

• Example: $\mathrm{HCl} + \mathrm{NaOH} \rightarrow \mathrm{NaCl} + \mathrm{H_2O}$

• Example: $2\mathrm{HNO_3} + \mathrm{Ca(OH)_2} \rightarrow 2\mathrm{H_2O} + \mathrm{Ca(NO_3)_2}$

• Example: $\mathrm{H_2SO_4} + \mathrm{Ca(OH)_2} \rightarrow 2\mathrm{H_2O} + \mathrm{CaSO_4}$

Equilibrium (When Reactions Are Partially Reversible)

• Equilibrium Constant ($K_{eq}$): Describes the ratio of product to reactant concentrations at equilibrium.

• Expression: $K_{eq} = \frac{[\text{Products}]}{[\text{Reactants}]}$ (exclude solids and pure liquids)

• Equilibrium can be shifted by:

  • Adding/removing reactants or products

  • Changing temperature

  • Changing pressure (for gases)

Le Châtelier’s Principle

If a system at equilibrium is disturbed, it will shift to counteract the disturbance.

• Adding reactants or removing products shifts equilibrium toward products.

• Adding products or removing reactants shifts equilibrium toward reactants.

• Heat and endothermic/exothermic reactions:

  • Heat as a reactant: favors products

  • Heat as a product: favors reactants

Weak Acids and Bases

• Only partially ionize in water.

• Equilibrium constants ($K_a$ for acids, $K_b$ for bases) describe their strength.

Conjugate Acids and Bases

• Every acid has a conjugate base, and every base has a conjugate acid.

• Example: $\mathrm{NH_3} + \mathrm{H_2O} \rightleftharpoons \mathrm{NH_4^+} + \mathrm{OH^-}$

pH and pOH Calculations

• pH: Measures acidity of a solution.

  • $\mathrm{pH} = -\log[\mathrm{H^+}]$

• pOH: Measures basicity of a solution.

  • $\mathrm{pOH} = -\log[\mathrm{OH^-}]$

• Relationship: $\mathrm{pH} + \mathrm{pOH} = 14$

Proteins

Amino Acids: Recognize Categories

Amino acids are the building blocks of proteins. Their structures vary by R group (side chain).

• General structure:

  • Central carbon (alpha carbon) bonded to:

    • Amino group (-NH2)

    • Carboxyl group (-COOH)

    • Hydrogen atom

    • R group (side chain)

All Amino Acids Used in Proteins are L-Isomers

• L and D refer to the arrangement around the alpha carbon.

• Proteins use only L-amino acids.

Recognizing Amino Acid Categories

• Nonpolar

• Polar

• Acidic

• Basic

Essential Amino Acids

• There are 9 essential amino acids that must be obtained from the diet.

Peptide Bonds

• Formed through condensation (dehydration) reactions:

$\mathrm{Amino\ acid}_1 + \mathrm{Amino\ acid}_2 \rightarrow \mathrm{Dipeptide} + \mathrm{H_2O}$

• Hydrogen bonds formed through peptide bonds are crucial to higher-level structures of proteins.

Protein Structure

• Primary Structure: Sequence of amino acids in a chain.

• Secondary Structure: Hydrogen bonding forms structures such as:

  • Alpha-helix: coiled

  • Beta-sheet: flat and stretched out

• Tertiary Structure: Overall 3D shape stabilized by interactions such as:

  • Hydrophobic interactions

  • Hydrogen bonds

  • Salt bridges

  • Disulfide bonds

• Quaternary Structure: Multiple polypeptide chains assemble for function.

Denaturation of Proteins

• Denaturation disrupts secondary, tertiary, and quaternary structures, often by heat or chemicals.

• Denatured proteins lose their function.

Protein Functions

• Enzymes: Catalyze biochemical reactions.

• Antibodies: Recognize and bind antigens for immune defense.

• Structural: Collagen in skin, keratin in hair.

Enzyme Activity

• Enzymes lower activation energy, increasing reaction rates.

• Lock-and-key model: Substrate fits exactly into enzyme active site.

• Induced fit model: Enzyme changes shape to fit substrate.

• Proximity: Enzyme holds reactants close together, increasing reaction likelihood.