CHEM 102 Exam 4 Study Guide: Solution Chemistry and Acids/Bases (Ch. 8-9)

Chapter 8: Solution Chemistry

Identifying Solutions and Their Physical Properties

Solutions are homogeneous mixtures composed of a solute dissolved in a solvent. Understanding the differences between solutions, colloids, and suspensions is essential for predicting their behavior and properties.

• Solute: The substance present in a lesser amount, dissolved in the solvent.

• Solvent: The substance present in a greater amount, which dissolves the solute.

• Solution: Homogeneous mixture; particles are molecular or ionic in size and do not settle out.

• Colloid: Heterogeneous mixture; particles are larger than in solutions but do not settle out (e.g., milk).

• Suspension: Heterogeneous mixture; particles are large enough to settle out over time (e.g., muddy water).

Example: Salt water is a solution; milk is a colloid; sand in water is a suspension.

Effects of Temperature and Pressure on Solution Formation

The solubility of substances depends on temperature and, for gases, pressure.

• Saturated Solution: Contains the maximum amount of solute that can dissolve at a given temperature.

• Dilute Solution: Contains a small amount of solute relative to the solvent.

• Temperature Effect: Solubility of solids generally increases with temperature; solubility of gases decreases with temperature.

• Pressure Effect (for gases): Solubility of gases increases with increasing pressure (Henry's Law).

Example: More sugar dissolves in hot tea than in cold; carbonated beverages lose fizz (CO2) faster when warm.

Chemical Equations for Hydration and Dissociation

Electrolytes dissociate in water to form ions, while nonelectrolytes do not. The degree of dissociation determines the strength of the electrolyte.

• Strong Electrolyte: Fully dissociates into ions (e.g., NaCl).

• Weak Electrolyte: Partially dissociates (e.g., acetic acid).

• Nonelectrolyte: Does not dissociate (e.g., glucose).

Example Equations:

• NaCl (s) $\rightarrow$ Na+ (aq) + Cl- (aq) (strong electrolyte)

• CH3COOH (aq) $\rightleftharpoons$ CH3COO- (aq) + H+ (aq) (weak electrolyte)

• C6H12O6 (s) $\rightarrow$ C6H12O6 (aq) (nonelectrolyte)

Milliequivalents and Conversions

Milliequivalents (mEq) are used to express the amount of ions in solution, especially in biological contexts.

• 1 Equivalent (Eq): Amount of ion that supplies 1 mole of charge.

• Conversion: $\text{mEq} = \text{mmol} \times |\text{charge}|$

• To convert Eq to moles: $\text{mol} = \frac{\text{Eq}}{|\text{charge}|}$

Example: 1 mmol Ca2+ = 2 mEq

Concentration Units

Concentration expresses the amount of solute in a given amount of solution. Common units include molarity, percent, ppm, and ppb.

• Molarity (M): $\text{M} = \frac{\text{mol solute}}{\text{L solution}}$

• Percent by mass: $\% = \frac{\text{g solute}}{\text{g solution}} \times 100$

• Parts per million (ppm): $\text{ppm} = \frac{\text{mg solute}}{\text{kg solution}}$

• Parts per billion (ppb): $\text{ppb} = \frac{\mu\text{g solute}}{\text{kg solution}}$

Dilution Calculations

Dilution involves adding solvent to decrease the concentration of a solution. The dilution equation relates initial and final concentrations and volumes.

• Dilution Equation: $C_1V_1 = C_2V_2$

• Application: Used to calculate unknown concentrations or volumes after dilution.

Example: To prepare 100 mL of 0.1 M NaCl from 1.0 M stock: $V_1 = \frac{C_2V_2}{C_1} = \frac{0.1 \times 100}{1.0} = 10$ mL stock needed.

Osmosis and Tonicity

Osmosis is the movement of water across a semipermeable membrane from low to high solute concentration. Tonicity describes the relative solute concentrations of two solutions separated by a membrane.

• Isotonic: Equal solute concentration on both sides; no net water movement.

• Hypotonic: Lower solute concentration outside; water enters the cell (cell swells).

• Hypertonic: Higher solute concentration outside; water leaves the cell (cell shrinks).

Example: Red blood cells in pure water (hypotonic) swell and may burst.

Transport Across Cell Membranes

Substances cross cell membranes by different mechanisms, depending on their properties and the cell's needs.

• Passive Diffusion: Movement from high to low concentration without energy input.

• Facilitated Transport: Movement via protein channels or carriers; no energy required.

• Active Transport: Movement against concentration gradient; requires energy (ATP).

Chapter 9: Acids, Bases, and Buffers

Properties of Acids and Bases

Acids and bases have distinct physical and chemical properties, and can be defined by different theories.

• Acid: Tastes sour, turns litmus red, reacts with metals; produces H+ in water (Arrhenius), or donates a proton (Brønsted-Lowry).

• Base: Tastes bitter, feels slippery, turns litmus blue; produces OH- in water (Arrhenius), or accepts a proton (Brønsted-Lowry).

Example: HCl is an acid; NaOH is a base.

Neutralization Reactions

Acids and bases react to form water and a salt in a neutralization reaction.

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

• Strong Bases: Group 1 and 2 metal hydroxides (e.g., NaOH, KOH, Ca(OH)2)

• Neutralization Equation: $\text{Acid} + \text{Base} \rightarrow \text{Salt} + \text{Water}$

Example: $\text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O}$

Chemical Equilibrium and Le Chatelier's Principle

Chemical equilibrium occurs when the rates of the forward and reverse reactions are equal. Le Chatelier's principle predicts how a system at equilibrium responds to disturbances.

• Equilibrium Expression: $K = \frac{[\text{products}]}{[\text{reactants}]}$ (for gases and aqueous species only)

• Le Chatelier's Principle: A system at equilibrium will shift to counteract a change in concentration, temperature, or pressure.

Weak Acid-Base Equilibria

Weak acids and bases do not fully dissociate in water. Their strengths are quantified by equilibrium constants and pKa values.

• Weak Acid Equilibrium: $\text{HA} + \text{H}_2\text{O} \rightleftharpoons \text{A}^- + \text{H}_3\text{O}^+$

• pKa: $\text{p}K_a = -\log K_a$; lower pKa means stronger acid.

• Conjugate Acid-Base Pairs: Differ by one proton (e.g., NH4+/NH3).

Example: Acetic acid (CH3COOH) and acetate (CH3COO-).

pH Calculations

pH measures the acidity or basicity of a solution, based on the concentration of hydronium ions.

• pH Definition: $\text{pH} = -\log [\text{H}_3\text{O}^+]$

• Calculating [H3O+]: $[\text{H}_3\text{O}^+] = 10^{-\text{pH}}$

• Acidic Solution: pH < 7

• Neutral Solution: pH = 7

• Basic Solution: pH > 7

Relative Strengths of Weak Acids

The strength of a weak acid is inversely related to its pKa value.

• Lower pKa: Stronger acid

• Higher pKa: Weaker acid

• Relative Amounts: At pH = pKa, [A-] = [HA]

Pharmaceuticals: pH, pKa, and Charge

The ionization state of pharmaceuticals affects their solubility and ability to cross membranes. The Henderson-Hasselbalch equation relates pH, pKa, and the ratio of ionized to unionized forms.

• Henderson-Hasselbalch Equation: $\text{pH} = \text{p}K_a + \log \left( \frac{[A^-]}{[HA]} \right)$

• Charged Form: Usually more soluble in water, less able to cross lipid membranes.

• Uncharged Form: Less soluble in water, more able to cross membranes.

Example: At pH > pKa, weak acid is mostly in A- (ionized) form.

Buffers and the Bicarbonate Buffer System

Buffers resist changes in pH upon addition of acid or base. The bicarbonate buffer system is crucial for maintaining blood pH.

• Buffer: Mixture of weak acid and its conjugate base.

• Bicarbonate Buffer Equation: $\text{CO}_2 + \text{H}_2\text{O} \rightleftharpoons \text{H}_2\text{CO}_3 \rightleftharpoons \text{HCO}_3^- + \text{H}^+$

• Homeostasis: The body maintains pH within a narrow range; disruptions can cause acidosis or alkalosis.

• Le Chatelier's Principle: Increased CO2 (e.g., hypoventilation) shifts equilibrium to produce more H+ (lower pH); decreased CO2 (hyperventilation) raises pH.

Table: Comparison of Solution Types

Type	Particle Size	Appearance	Separation
Solution	< 1 nm	Clear	Not separated by filtration
Colloid	1-1000 nm	Cloudy	Not separated by filtration
Suspension	> 1000 nm	Cloudy, settles	Separated by filtration

Table: Strong Acids and Bases

Strong Acid	Formula
Hydrochloric acid	HCl
Hydrobromic acid	HBr
Hydroiodic acid	HI
Nitric acid	HNO3
Sulfuric acid	H2SO4
Perchloric acid	HClO4

Strong Base	Formula
Sodium hydroxide	NaOH
Potassium hydroxide	KOH
Calcium hydroxide	Ca(OH)2