Acid-Base Titration
Neutralization & Volumetric Analysis | Chemistry
1. What is Acid-Base Titration?
Definition: A method to determine the concentration of an acid or base by neutralizing it with a standard solution of base or acid of known concentration.
The core reaction is Neutralization:
$$ H^+ (aq) + OH^- (aq) \rightarrow H_2O (l) $$Key Terms:
- Titrant: The solution in the burette (Known concentration).
- Titrand (Analyte): The solution in the flask (Unknown concentration).
- Equivalence Point: The theoretical point where equivalents of acid = equivalents of base.
- End Point: The experimental point where the indicator changes color.
2. The Law of Equivalence
At the equivalence point, the number of gram equivalents of acid equals the number of gram equivalents of base.
$$ N_1 V_1 = N_2 V_2 $$
Where $N$ is Normality and $V$ is Volume.
3. Choice of Indicators
Indicators are weak organic acids or bases that change color depending on the pH of the medium. The choice depends on the pH range at the equivalence point.
| Titration Type | pH Range at Eq. Point | Suitable Indicator |
|---|---|---|
| Strong Acid vs Strong Base (e.g., HCl vs NaOH) |
pH = 7 | Any (Methyl Orange, Phenolphthalein) |
| Weak Acid vs Strong Base (e.g., CH3COOH vs NaOH) |
pH > 7 (Basic range ~8-10) | Phenolphthalein (8.3 - 10) |
| Strong Acid vs Weak Base (e.g., HCl vs NH4OH) |
pH < 7 (Acidic range ~4-6) | Methyl Orange (3.1 - 4.4) |
| Weak Acid vs Weak Base | No sharp pH change | No simple indicator works |
4. Standard Solutions
- Primary Standard: A substance available in high purity, stable in air, and can be weighed directly to make a standard solution (e.g., Oxalic Acid, Sodium Carbonate).
- Secondary Standard: A solution whose concentration changes over time (hygroscopic) and must be standardized against a primary standard (e.g., NaOH, HCl).
Practice Quiz
Test your knowledge on Titration.
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