Understanding Acid-Base Titration
Titration is a fundamental analytical technique in chemistry used to determine the concentration of an unknown solution by reacting it with a solution of known concentration. Acid-base titration, specifically, involves neutralization reactions between acids and bases, and is one of the most common types of volumetric analysis.
What is Titration?
In a titration, a solution of known concentration (the titrant) is gradually added to a known volume of solution with unknown concentration (the analyte) until the reaction reaches completion. This completion point, called the equivalence point, is often detected using an indicator that changes color or by monitoring pH.
n₁M₁V₁ = n₂M₂V₂
Where n is the n-factor (number of H+ or OH- ions per molecule).
Why Titration Matters
- Quantitative analysis: Accurately determine unknown concentrations
- Quality control: Verify product concentrations in manufacturing
- Environmental testing: Measure water quality and pollutant levels
- Food industry: Determine acidity in beverages and foods
- Pharmaceuticals: Assay drug concentrations
- Research: Characterize new compounds and reactions
Titration Calculation Formula
For simple 1:1 stoichiometry (like HCl + NaOH):
M₁V₁ = M₂V₂
For reactions with different stoichiometry (like H₂SO₄ + 2NaOH):
n₁M₁V₁ = n₂M₂V₂
Where n represents the n-factor or number of acidic hydrogens (for acids) or hydroxide ions (for bases).
Example Calculation
25.0 mL of 0.1 M HCl is used to titrate 20.0 mL of NaOH solution. Find the concentration of NaOH:
- M₁V₁ = M₂V₂
- (0.1 M)(25.0 mL) = M₂(20.0 mL)
- M₂ = (0.1 × 25.0) / 20.0
- M₂ = 0.125 M
Types of Acid-Base Titrations
- Strong acid - strong base: Sharp pH change at equivalence point (pH 7)
- Strong acid - weak base: Equivalence point pH < 7
- Weak acid - strong base: Equivalence point pH > 7
- Weak acid - weak base: No sharp endpoint, rarely used
Common Indicators
- Phenolphthalein: Colorless to pink (pH 8.2-10), used for strong acid-base titrations
- Methyl orange: Red to yellow (pH 3.1-4.4), used for strong acid-weak base
- Bromothymol blue: Yellow to blue (pH 6.0-7.6), general purpose
- Universal indicator: Multiple color changes across pH range
Equipment and Procedure
Essential titration equipment includes:
- Burette: For delivering precise volumes of titrant
- Pipette: For measuring exact volumes of analyte
- Erlenmeyer flask: For mixing the solutions
- pH meter or indicator: For detecting the endpoint
- White tile: To better see color changes
Standard Solutions
The titrant must be a standard solution - one with accurately known concentration. Primary standards are highly pure compounds used to prepare standard solutions. Common primary standards include:
- Sodium carbonate (Na₂CO₃) - for standardizing acids
- Potassium hydrogen phthalate (KHP) - for standardizing bases
- Oxalic acid (H₂C₂O₄) - for standardizing bases
Sources of Error
- Parallax error: Reading burette from wrong angle
- Air bubbles: In burette tip affecting volume
- Overshooting endpoint: Adding titrant too quickly
- Contamination: Dirty glassware affecting results
- Incorrect indicator: Choosing wrong pH range
- Temperature effects: Volume changes with temperature
Tips for Accurate Titrations
- Rinse burette with titrant solution before filling
- Remove air bubbles from burette tip
- Add titrant slowly near the endpoint
- Swirl flask constantly during titration
- Perform multiple trials and average results
- Read meniscus at eye level
- Use appropriate indicator for the titration type
Beyond Acid-Base Titrations
Other types of titrations include:
- Redox titrations: Involve electron transfer (e.g., KMnO₄ titrations)
- Complexometric titrations: Form complex ions (e.g., EDTA for metal ions)
- Precipitation titrations: Form precipitates (e.g., silver nitrate for chloride)
Applications in Industry
- Water treatment: Measuring alkalinity and hardness
- Wine making: Determining titratable acidity
- Dairy industry: Testing milk acidity
- Chemical manufacturing: Quality control of products
- Petroleum industry: Measuring acid or base number of oils
Whether you're a chemistry student performing laboratory experiments, an analyst conducting quality control tests, or a researcher quantifying compounds, our titration calculator provides quick, accurate concentration determinations from your titration data.