Comprehensive Study Guide: Solutions, Acids & Bases, and Hydrocarbons

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): $\%\ (m/m) = \frac{\text{mass of solute (g)}}{\text{mass of solution (g)}} \times 100$

• Percent by volume (% v/v): $\%\ (v/v) = \frac{\text{volume of solute (mL)}}{\text{volume of solution (mL)}} \times 100$

• Percent mass/volume (% m/v): $\%\ (m/v) = \frac{\text{mass of solute (g)}}{\text{volume of solution (mL)}} \times 100$

• Molarity (M): $M = \frac{\text{moles of solute}}{\text{liters of solution}}$

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:

• $M_1V_1 = M_2V_2$

• Where $M_1$ and $V_1$ are the initial molarity and volume, and $M_2$ and $V_2$ are the final molarity and volume.

• Example: To dilute 15.0 mL of 0.050 M NaCl to 60.0 mL, $M_2 = \frac{M_1V_1}{V_2}$

Types of Mixtures: Solutions, Colloids, and Suspensions

Mixtures can be classified based on particle size and behavior:

Type	Particle Size	Appearance	Separation
Solution	< 1 nm	Clear, homogeneous	Not separated by filtration
Colloid	1–1000 nm	Cloudy, scatters light (Tyndall effect)	Not separated by filtration
Suspension	> 1000 nm	Cloudy, heterogeneous	Particles settle, can be filtered

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.

Type	Definition	Effect on Red Blood Cells
Isotonic	Equal solute concentration	No net water movement; cell remains normal
Hypotonic	Lower solute concentration outside	Water enters cell; cell swells (hemolysis)
Hypertonic	Higher solute concentration outside	Water leaves cell; cell shrinks (crenation)

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: $pH = -\log_{10}[H_3O^+]$

• pOH: $pOH = -\log_{10}[OH^-]$

• Relationship: $pH + pOH = 14$

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: $NH_3 + H_2O \rightleftharpoons NH_4^+ + OH^-$

Equilibrium

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

• Example: $A + B \rightleftharpoons C + D$

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: $HCl + NaOH \rightarrow NaCl + H_2O$

• Use molarity as a conversion factor: $M_1V_1 = M_2V_2$

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: $H_2PO_4^- / HPO_4^{2-}$ buffer system.

• Acid added: $HPO_4^{2-} + H^+ \rightarrow H_2PO_4^-$

• Base added: $H_2PO_4^- + OH^- \rightarrow HPO_4^{2-} + H_2O$

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: $0.45\% = \frac{\text{g NaCl}}{250\ \text{mL}} \times 100$

• To dilute: Use $M_1V_1 = M_2V_2$.

Ion Concentrations and mEq/L

• When salts dissolve, they dissociate into ions.

• Example: $NaCl \rightarrow Na^+ + Cl^-$

• mEq/L: $\text{mEq/L} = \text{mmol/L} \times \text{charge}$

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: $CH_3CH_2CH_2COOH + O_2 \rightarrow CO_2 + H_2O$ (balance as needed)

• Hydrogenation: $CH_2=CH_2 + H_2 \rightarrow CH_3CH_3$

• Hydration: $CH_2=CH_2 + H_2O \rightarrow CH_3CH_2OH$

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

Type	Definition	Example	Behavior in Water
Strong Electrolyte	Completely dissociates	NaCl	Conducts electricity well
Weak Electrolyte	Partially dissociates	CH3COOH	Conducts electricity weakly
Nonelectrolyte	No dissociation	Glucose	Does not conduct electricity

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.