Solutions and Their Properties

Definition and Components of a Solution

A solution is a homogeneous mixture composed of two or more substances. The solute is the substance present in a lesser amount and is dissolved in the solvent, which is present in a greater amount.

• Solvent: The component in greater quantity; often water in aqueous solutions.

• Solute: The component in lesser quantity; the substance being dissolved.

• Example: In salt water, NaCl is the solute and water is the solvent.

Concentration Units and Calculations

Concentration expresses the amount of solute in a given amount of solution or solvent. Common units include:

• Percent by mass (% m/m):

• Percent by volume (% v/v):

• Percent mass/volume (% m/v):

• Molarity (M):

These units can be used as conversion factors in calculations.

Dilution of Solutions

Dilution involves adding solvent to a solution to decrease its concentration. The relationship is given by:

• Where and are the initial molarity and volume, and and are the final molarity and volume.

• Example: To dilute 15.0 mL of 0.050 M NaCl to 60.0 mL,

Types of Mixtures: Solutions, Colloids, and Suspensions

Mixtures can be classified based on particle size and behavior:

Osmosis, Diffusion, and Tonicity

• Diffusion: Movement of particles from high to low concentration.

• Osmosis: Movement of water across a semipermeable membrane from low to high solute concentration.

• Osmotic Pressure: The pressure required to stop osmosis.

• Tonicity: Describes the relative solute concentration of two solutions separated by a membrane.

Solubility and Polarity

• "Like dissolves like": Polar solvents dissolve polar solutes; nonpolar solvents dissolve nonpolar solutes.

• Polarity: Determined by molecular structure and electronegativity differences.

• Example: CH3F (polar) is more soluble in water (polar) than CCl4 (nonpolar).

Intermolecular forces (hydrogen bonding, dipole-dipole, London dispersion) influence solubility.

Electrolytes and Nonelectrolytes

• Strong electrolytes: Completely dissociate in water (e.g., NaCl).

• Weak electrolytes: Partially dissociate (e.g., acetic acid).

• Nonelectrolytes: Do not dissociate (e.g., sugar).

Acids, Bases, and Equilibrium

Acids, Bases, and pH

• Acid: Substance that donates a proton (H+).

• Base: Substance that accepts a proton or donates OH-.

• pH:

• pOH:

• Relationship:

Classify solutions:

• Acidic: pH < 7

• Neutral: pH = 7

• Basic: pH > 7

Conjugate Acid-Base Pairs

• When an acid donates a proton, it forms its conjugate base.

• When a base accepts a proton, it forms its conjugate acid.

• Example:

Equilibrium

• Chemical equilibrium: The rate of the forward reaction equals the rate of the reverse reaction; concentrations remain constant.

• Example:

Strong vs. Weak Acids

• Strong acids: Completely ionize in water (e.g., HCl).

• Weak acids: Partially ionize (e.g., CH3COOH).

• Relative concentrations: Strong acids produce more H3O+ than weak acids at the same concentration.

Neutralization and Titration

• Neutralization: Acid reacts with base to form water and a salt.

• Titration: Analytical technique to determine concentration by reacting a known volume with a standard solution.

• Example equation:

• Use molarity as a conversion factor:

Buffers

• Buffer: Solution that resists changes in pH upon addition of small amounts of acid or base.

• Composed of a weak acid and its conjugate base (or weak base and its conjugate acid).

• Example: buffer system.

• Acid added:

• Base added:

Preparation and Calculation of Solutions

Preparing Solutions of Specific Concentration

• To prepare a % (m/v) solution: Dissolve the required mass of solute in enough solvent to reach the desired final volume.

• To prepare a molar solution: Calculate moles needed, weigh out solute, and dilute to final volume.

• Example: To make 250 mL of 0.45% (m/v) NaCl:

• To dilute: Use .

Ion Concentrations and mEq/L

• When salts dissolve, they dissociate into ions.

• Example:

• mEq/L:

Hydrocarbons and Organic Chemistry

Types and Naming of Hydrocarbons

• Alkanes: Saturated hydrocarbons (single bonds only).

• Alkenes: Unsaturated hydrocarbons (at least one double bond).

• Alkynes: Unsaturated hydrocarbons (at least one triple bond).

• Aromatic compounds: Contain benzene ring(s).

• Can be straight-chain, branched, or cyclic.

Structural Representations

• Condensed formula: Shows all atoms in a linear form (e.g., CH3CH2CH3).

• Structural formula: Shows all bonds between atoms.

• Skeletal (line-angle) formula: Lines represent carbon chains; hydrogens on carbons are implied.

Cis-Trans Isomerism in Alkenes

• Cis isomer: Substituents on the same side of the double bond.

• Trans isomer: Substituents on opposite sides of the double bond.

Saturated vs. Unsaturated Hydrocarbons

• Saturated: Only single C–C bonds (alkanes).

• Unsaturated: Contains double or triple C–C bonds (alkenes, alkynes).

Reactions of Hydrocarbons

• Combustion: Hydrocarbon reacts with O2 to form CO2 and H2O.

• Hydrogenation: Addition of H2 to alkenes/alkynes to form alkanes.

• Hydration: Addition of H2O to alkenes to form alcohols.

Example:

• Combustion: (balance as needed)

• Hydrogenation:

• Hydration:

Aromatic Compounds

• Benzene: Six-membered ring with alternating double bonds (delocalized electrons).

• Properties: Stable, undergoes substitution rather than addition reactions.

• Derivatives: Toluene (methylbenzene), phenol (hydroxybenzene), etc.

Summary Table: Electrolytes

Additional info:

• Lewis structures and intermolecular forces can be used to justify solubility trends.

• For solution preparation, always add solute first, then dilute to final volume.

• For titration, the endpoint is detected by an indicator or pH meter.