Understanding Acid-Base Titration: Principles and Practice

Expert reviewed • 22 November 2024 • 6 minute read

Introduction

Titration is a fundamental analytical technique in chemistry used to determine the precise concentration of a solution. This quantitative method is particularly important in acid-base analysis, where it enables chemists to measure unknown concentrations with high accuracy.

Types of Acid-Base Titration

There are two main approaches to acid-base titration:

  • Indicator-based titration: Uses chemical indicators that change color at the equivalence point
  • Conductometric titration: Measures changes in electrical conductivity to determine the endpoint

Understanding Standard Solutions

A standard solution is a solution of precisely known concentration. In acid-base titration:

  • If analyzing an unknown base, use an acid standard solution
  • If analyzing an unknown acid, use a base standard solution

Primary Standards

A primary standard must meet these essential criteria:

  • High chemical purity
  • Known, stable composition
  • Moisture-free
  • Good water solubility
  • High molar mass

Common examples of reliable primary standards include:

  • Oxalic acid
  • Benzoic acid
  • Anhydrous sodium carbonate
  • Anhydrous sodium hydrogen carbonate

Secondary Standards

Secondary standards, such as sodium hydroxide (NaOH), require standardization against a primary standard before use. They are less preferred due to:

  • Additional standardization steps
  • Increased potential for error
  • Reduced accuracy

Preparing a Standard Solution

Let's walk through preparing a standard sodium carbonate solution:

  • Calculate required mass For a 250.0 mL solution of 0.0500 mol/L Na2CO3\text{Na}_2\text{CO}_3:

    n=c×V=0.0500 mol/L×0.250 L=0.0125 moln = c \times V = 0.0500 \text{ mol/L} \times 0.250 \text{ L} = 0.0125 \text{ mol}

    m=n×MM=0.0125×(2×22.99+12.01+3×16.00)m = n \times \text{MM} = 0.0125 \times (2 \times 22.99 + 12.01 + 3 \times 16.00)

    m=1.33 gm = 1.33 \text{ g}

  • Dissolution Process

    • Dissolve the weighed solid in distilled water
    • Use a clean beaker and stirring rod

  • Solution Transfer

    • Transfer to a 250.0 mL volumetric flask
    • Rinse equipment with distilled water
    • Add washings to the flask

  • Volume Adjustment

    • Fill to approximately 1 cm below mark
    • Add dropwise to reach meniscus

  • Homogenization

    • Stopper and invert 10 times

Equipment Preparation

Burette Setup

  • Clean with distilled water
  • Rinse with titrant solution
  • Fill and record initial volume
  • Ensure no air bubbles in tip

Conical Flask Preparation

  • Rinse with distilled water
  • Add measured aliquot using pipette
  • Add appropriate indicator
  • Place on white tile for visibility

Sample Calculation

For a titration where 50.00 mL of HCl neutralizes 20.00 mL of 0.0500 mol/L Na2CO3\text{Na}_2\text{CO}_3:

Na2CO3+2HCl→2NaCl+H2O+CO2\text{Na}_2\text{CO}_3 + 2\text{HCl} \rightarrow 2\text{NaCl} + \text{H}_2\text{O} + \text{CO}_2

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