Strong acid–strong base reactions | Acids and bases | AP Chemistry | Khan Academy
Hydrochloric Acid and Sodium Hydroxide: Understanding Acid-Base Reactions
Overview of Acid-Base Neutralization
- Hydrochloric acid (HCl) is identified as a strong acid, while sodium hydroxide (NaOH) is recognized as a strong base. Their reaction produces sodium chloride (NaCl) and water (H2O), indicating a complete reaction with no equilibrium.
- The reaction between HCl and NaOH is classified as an acid-base neutralization reaction, characterized by the complete ionization of both reactants in solution.
Ionization of Reactants
- In solution, HCl fully dissociates into hydrogen ions (H⁺) and chloride ions (Cl⁻). Similarly, NaOH dissociates completely into sodium ions (Na⁺) and hydroxide ions (OH⁻).
- The products include aqueous sodium cations (Na⁺), chloride anions (Cl⁻), and water, which remains un-ionized in this context.
Ionic Equations
- The overall ionic equation for the reaction can also be referred to as the complete ionic equation. This equation helps derive the net ionic equation by identifying spectator ions.
- Spectator ions are those that do not participate in the chemical change; here, Na⁺ and Cl⁻ are canceled out from both sides of the equation.
Net Ionic Equation
- After removing spectator ions, the net ionic equation simplifies to H⁺ + OH⁻ → H₂O. Alternatively, using hydronium ion notation gives 2 H₃O⁺ + 2 OH⁻ → 2 H₂O.
Reaction Completion Analysis
- When equal moles of strong acid and base react—like 1 mole each of HCl and NaOH—the resulting solution will have a pH of 7 due to complete neutralization at standard conditions.
Calculating pH in Unequal Molar Solutions
Example Calculation Setup
- A scenario is presented where 300 mL of 1.0 M HCl reacts with 100 mL of 1.0 M NaOH. The goal is to calculate the resulting pH after this reaction occurs.
Molarity Calculations
- For HCl:
- Volume = 300 mL = 0.300 L
- Moles = molarity × volume = 1.0 × 0.300 = 0.30 moles.
- For NaOH:
- Volume = 100 mL = 0.100 L
- Moles = molarity × volume = 1.0 × 0.100 = 0.10 moles.
Ion Concentration Post-Reaction
- After determining initial concentrations:
- Hydronium Ions: From .30 moles of HCl → .30 moles of H₃O⁺.
- Hydroxide Ions: From .10 moles of NaOH → .10 moles of OH⁻.
Hydronium and Hydroxide Ion Reaction Analysis
Understanding the Net Ionic Equation
- The net ionic equation is presented as hydronium ion plus hydroxide ion forming 2H₂O, indicating a neutralization reaction.
- An ICF (Initial, Change, Final) table is utilized to track the moles of reactants: initial moles of hydronium ions are 0.30 and hydroxide ions are 0.10.
- Due to unequal amounts of moles and a one-to-one mole ratio, there will be a limiting reactant (hydroxide ions) and an excess reactant (hydronium ions).
Reaction Completion and Molar Calculations
- All 0.10 moles of hydroxide ions will react with an equal amount of hydronium ions, leading to a decrease in hydronium from 0.30 to 0.20 moles.
- The hydroxide ions are identified as the limiting reactant while the hydronium ions remain in excess after the reaction completes.
pH Calculation from Excess Hydronium Ions
- The pH of the resulting solution can be calculated based on the remaining moles of excess hydronium ions (0.20).