General Chemistry Study Notes: Acid-Base Equilibrium, Biomolecules, and Biochemical Processes

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Acid-Base Equilibrium

Bronsted-Lowry Acids and Bases

The Bronsted-Lowry theory defines acids as proton (H+) donors and bases as proton acceptors. This concept is fundamental to understanding acid-base reactions in aqueous solutions.

Acid: Substance that donates a proton.
Base: Substance that accepts a proton.
Conjugate Acid-Base Pair: When an acid donates a proton, it forms its conjugate base; when a base accepts a proton, it forms its conjugate acid.
Example: In the reaction NH3 + HCN → NH4+ + CN-, NH3 acts as a base, HCN as an acid, NH4+ as the conjugate acid, and CN- as the conjugate base.

pH and Acid Strength

pH is a measure of the hydrogen ion concentration in a solution and is used to determine acidity or basicity.

pH Scale: Ranges from 0 (most acidic) to 14 (most basic).
Acidic Solution: pH < 7
Neutral Solution: pH = 7
Basic Solution: pH > 7
Formula:
Example: If [H+] = 1.2 × 10-12 M,

Acid and Base Strength

The strength of an acid or base is determined by its ability to dissociate in water.

Strong Acid: Completely dissociates in water (e.g., HCl).
Weak Acid: Partially dissociates (e.g., HCN).
Strong Base: Completely dissociates (e.g., NaOH).
Weak Base: Partially dissociates (e.g., NH3).

Biomolecules: Structure and Function

Amino Acids and Proteins

Amino acids are the building blocks of proteins. Each amino acid contains a central carbon (the alpha carbon) bonded to an amino group, a carboxyl group, a hydrogen atom, and a unique side chain (R group).

Chiral Centers: Most amino acids (except glycine) have a chiral alpha carbon.
Protein Structure:
- Primary: Sequence of amino acids.
- Secondary: Local folding (e.g., alpha helix, beta sheet).
- Tertiary: Overall 3D structure.
- Quaternary: Arrangement of multiple polypeptide chains.
Example: Hemoglobin has quaternary structure composed of four polypeptide subunits.

Enzymes

Enzymes are biological catalysts that speed up chemical reactions in living organisms.

Function: Lower activation energy, increase reaction rate.
Specificity: Each enzyme acts on a specific substrate.
Example: Amylase catalyzes the breakdown of starch into sugars.

Nucleic Acids

Nucleic acids (DNA and RNA) are polymers of nucleotides, which consist of a sugar, a phosphate group, and a nitrogenous base.

DNA: Contains deoxyribose sugar; bases include adenine, thymine, cytosine, guanine.
RNA: Contains ribose sugar; bases include adenine, uracil, cytosine, guanine.
Example: Adenine is found in both DNA and RNA, while uracil is unique to RNA.

Carbohydrates

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen. They serve as energy sources and structural components.

Monosaccharides: Simple sugars (e.g., glucose).
Disaccharides: Two monosaccharides joined (e.g., sucrose).
Polysaccharides: Long chains (e.g., starch, cellulose).
Example: The backbone of DNA contains five carbon atoms from the deoxyribose sugar.

Biochemical Processes

Catabolism and Anabolism

Metabolism consists of two main processes: catabolism (breakdown of molecules) and anabolism (synthesis of molecules).

Catabolism: Converts large molecules into smaller ones, releasing energy.
Anabolism: Builds large molecules from smaller ones, consuming energy.
Example: Cellular respiration is a catabolic process; protein synthesis is anabolic.

Digestion and Absorption

Digestion involves breaking down food into smaller molecules for absorption and use by the body.

Carbohydrate Digestion: Begins in the mouth with amylase, continues in the small intestine.
Lipid Digestion: Involves emulsification by bile and breakdown by lipases.
Protein Digestion: Begins in the stomach with pepsin, continues in the small intestine.

Chemical Equilibrium

Equilibrium Expressions

Chemical equilibrium occurs when the rates of the forward and reverse reactions are equal, and the concentrations of reactants and products remain constant.

Equilibrium Constant (K): Expresses the ratio of product concentrations to reactant concentrations at equilibrium.
General Formula: For the reaction :

Example: For the reaction C(s) + 2 I2(g) → CI4(g):

Additional info:

Some questions reference biochemistry topics (e.g., enzymes, nucleic acids, metabolism) that overlap with general chemistry, especially in introductory college courses.
For more advanced biochemistry, consult a dedicated biochemistry textbook.