뒤로Reactions in Aqueous Solutions: Electrolytes, Solution Stoichiometry, and Ionic Processes
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Reactions in Aqueous Solutions
Introduction to Solutions
Solutions are homogeneous mixtures composed of two or more substances. The composition is uniform throughout, and the components can be gases, liquids, or solids.
Solvent: The component present in the largest amount; determines the state of the solution.
Solute: The substance(s) dissolved in the solvent.
Examples of Common Solutions:
Solution | Components |
|---|---|
Gaseous solutions | Air (N2, O2, etc.), Natural gas (CH4, C2H6, etc.) |
Liquid solutions | Seawater (H2O, NaCl), Vinegar (H2O, CH3COOH), Soda pop (H2O, CO2, C12H22O11) |
Solid solutions | Yellow brass (Cu, Zn), Palladium-hydrogen (Pd, H2) |
Electrolytes and Nonelectrolytes
Substances dissolved in water can be classified based on their ability to conduct electricity:
Electrolyte: A substance that, when dissolved in water, produces a solution that conducts electricity due to the presence of ions.
Nonelectrolyte: A substance that, when dissolved, does not produce ions and thus does not conduct electricity.
Types of Electrolytes:
Strong Electrolyte: Completely dissociates into ions in solution (e.g., NaCl, HCl).
Weak Electrolyte: Partially dissociates; only some molecules form ions (e.g., CH3COOH).
Demonstration: A lightbulb glows brightly with a strong electrolyte, dimly with a weak electrolyte, and not at all with a nonelectrolyte.
Classification of Solutes in Aqueous Solution
Solutes can be classified as strong or weak electrolytes based on their degree of ionization in water.
Strong Electrolyte | Weak Electrolyte |
|---|---|
HCl, HNO3, HClO4, H2SO4, NaOH, Ba(OH)2, Ionic compounds | CH3COOH, HF, HNO2, NH3, H2O |
Strong electrolytes dissociate 100% into ions:
Weak electrolytes partially dissociate and exist in equilibrium:
Hydration
Hydration is the process in which an ion is surrounded by water molecules arranged in a specific manner. When an ionic compound such as sodium chloride dissolves in water, the ions are separated and surrounded by water molecules.
Hydration shell: The cluster of water molecules surrounding an ion.
This process stabilizes ions in solution and is essential for the dissolution of ionic compounds.
Solution Stoichiometry
Concentration of Solutions
The concentration of a solution is the amount of solute present in a given quantity of solvent or solution. The most common unit is molarity (M):
Example: A 1.46 M C6H12O6 solution contains 1.46 mol of solute per 1 L of solution. For 0.730 mol in 500 mL:
Calculating Ion Concentrations
When ionic compounds dissolve, they dissociate into their constituent ions. The concentration of each ion depends on the stoichiometry of the dissociation.
Example 1: For 0.1 M MgCl2 solution:
Example 2: For 0.2 M Cr2(SO4)3 solution:
Summary Table: Ion Concentrations from Ionic Compounds
Compound | Dissociation | Ion Ratio |
|---|---|---|
MgCl2 | Mg2+ + 2Cl- | 1:2 |
Cr2(SO4)3 | 2Cr3+ + 3SO42- | 2:3 |
Key Terms and Concepts
Solution: Homogeneous mixture of two or more substances.
Solvent: The major component of a solution.
Solute: The minor component(s) dissolved in the solvent.
Electrolyte: Substance that produces ions in solution and conducts electricity.
Nonelectrolyte: Substance that does not produce ions in solution.
Molarity (M): Moles of solute per liter of solution.
Hydration: Surrounding of ions by water molecules in solution.
Additional info:
Strong electrolytes include most soluble salts, strong acids, and strong bases.
Weak electrolytes include weak acids and weak bases, which only partially ionize in water.
Nonelectrolytes include most molecular compounds (e.g., sugar, ethanol) that do not ionize in water.
