Back to Library

(AI-Powered Suggestions)

Related Topics

A topic from the subject of Titration in Chemistry.

  • 1 year ago
  • 6 min read
Molarity and Normality in Titration
Introduction

Titration is a quantitative analytical technique used in chemistry to determine the concentration of a solution. It involves the gradual addition of a solution of known concentration (the titrant) to a solution of unknown concentration (the analyte) until the reaction between them is complete. The point at which the reaction is complete is called the equivalence point or stoichiometric point.

Basic Concepts
  • Molarity (M): Molarity is a measure of the concentration of a solution, expressed as the number of moles of solute per liter of solution (mol/L).
  • Normality (N): Normality is a measure of the concentration of a solution, expressed as the number of equivalents of solute per liter of solution (eq/L). An equivalent is the amount of a substance that can react with or provide one mole of hydrogen ions (H+) in an acid-base reaction, or one mole of electrons in a redox reaction. The normality of a solution is always equal to or a multiple of its molarity.
Equipment and Techniques

Common equipment used in titration includes:

  • Buret: Delivers the titrant to the analyte.
  • Pipet: Measures the volume of the analyte.
  • Erlenmeyer flask or conical flask: Contains the analyte.
  • Indicator (e.g., phenolphthalein): Signifies the endpoint of the titration.
  • Magnetic stirrer (optional): Provides uniform mixing.

Titration Procedure:

  1. A known volume of the analyte is accurately measured using a pipet and transferred to an Erlenmeyer flask.
  2. A few drops of a suitable indicator are added to the analyte solution.
  3. The buret is filled with the titrant.
  4. The titrant is added slowly to the analyte while continuously swirling the flask. This continues until the indicator changes color, signaling the endpoint of the titration (which is close to the equivalence point).
  5. The volume of titrant used is carefully recorded.
Types of Titration
  • Acid-Base Titrations: These titrations determine the concentration of an acid or base by reacting it with a base or acid of known concentration, respectively.
  • Redox Titrations: These titrations involve the transfer of electrons between the titrant and the analyte. An example is titrating potassium permanganate (KMnO4) with iron(II) sulfate (FeSO4).
  • Complexometric Titrations: These titrations involve the formation of a complex ion between the titrant and the analyte. EDTA titrations are a common example used to determine metal ion concentrations.
  • Precipitation Titrations: These titrations involve the formation of a precipitate between the titrant and the analyte. An example is titrating silver nitrate (AgNO3) with sodium chloride (NaCl).
Data Analysis

The concentration of the unknown analyte is calculated using the following formula (assuming a 1:1 stoichiometric ratio between the titrant and analyte):

Concentration of analyte (M) = (Molarity of titrant × Volume of titrant) / Volume of analyte

For reactions with stoichiometric ratios other than 1:1, the appropriate stoichiometric factor must be included in the calculation.

Applications
  • Quality Control: Verifying the purity and concentration of chemicals in manufacturing and pharmaceutical industries.
  • Environmental Analysis: Determining the concentration of pollutants in water, soil, or air samples.
  • Clinical Chemistry: Measuring the concentrations of various substances in biological fluids.
  • Research: Studying reaction stoichiometry and kinetics.
Conclusion

Titration is a fundamental technique in analytical chemistry with broad applications in various fields. Understanding molarity and normality is crucial for accurate data analysis and interpretation of results. The selection of the appropriate titrant and indicator is essential for successful titrations.

Molarity and Normality in Titration

Molarity (M) measures the concentration of a solution in terms of moles of solute per liter of solution.

Normality (N) measures the concentration of a solution in terms of gram equivalents of solute per liter of solution.

Key Points:

  • For monoprotic acids and bases, molarity and normality are equal.
  • For polyprotic acids and bases, normality considers the number of ionizable protons or hydroxide ions. For example, a 1M solution of sulfuric acid (H₂SO₄) is 2N because it has two ionizable protons.
  • In titration, the equivalence point is reached when the moles of acid and base are equal (or, equivalently, when the equivalents of acid and base are equal).
  • The titrant is the solution of known concentration that is added to the analyte.
  • The analyte is the solution of unknown concentration that is being analyzed.

Main Concepts:

Titration is a technique used to determine the concentration of an unknown solution by reacting it with a solution of known concentration. This is often done using an indicator that changes color near the equivalence point. By measuring the volume of the known solution (the titrant) required to reach the equivalence point, the concentration of the unknown solution (the analyte) can be calculated.

For acid-base titrations, the fundamental equation used is based on the equivalence of moles (or equivalents):

Macid x Vacid = Mbase x Vbase

or, in terms of normality:

Nacid x Vacid = Nbase x Vbase

where:

  • Macid is the molarity of the acid solution
  • Vacid is the volume of the acid solution
  • Mbase is the molarity of the base solution
  • Vbase is the volume of the base solution

By understanding molarity and normality, chemists can accurately perform titrations to determine the concentration of unknown solutions. The choice between using molarity or normality depends on the specific reaction and the number of reactive sites on the acid or base.

Molarity and Normality in Titration Experiment
Objective:

To determine the molarity and normality of a given unknown acid solution through titration with a known base solution.

Materials:
  • Unknown acid solution
  • Known concentration base solution (e.g., NaOH, with its exact molarity specified)
  • Buret
  • Erlenmeyer flask
  • Phenolphthalein indicator
  • Magnetic stirrer and stir bar
  • Distilled water
  • Wash bottle
  • Pipet and pipet bulb (or volumetric pipet)
Procedure:
  1. Clean and rinse the buret with distilled water, followed by a small portion of the known base solution. Fill the buret with the known base solution, ensuring no air bubbles are present in the buret tip. Record the initial buret reading.
  2. Using a pipet, accurately measure a known volume (e.g., 25.00 mL) of the unknown acid solution into an Erlenmeyer flask. Add 2-3 drops of phenolphthalein indicator.
  3. Place the flask under the buret and begin magnetic stirring.
  4. Slowly add the base solution from the buret to the acid solution, while continuously swirling the flask. The swirling helps to mix the reactants thoroughly.
  5. As the endpoint approaches, the solution will begin to turn pink. Slow the addition of the base to a drop-wise rate.
  6. The endpoint is reached when a single drop of base causes a persistent faint pink color that remains for at least 30 seconds. Record the final buret reading.
  7. Repeat steps 2-6 for at least two more trials to ensure accuracy and calculate the average volume of base used.
Calculations:
Molarity (M):

Molarity (M) = Moles of acid / Volume of acid solution (L)

To determine the moles of acid, use the following formula (based on a balanced chemical equation assuming a monoprotic acid):

Moles of acid = Molarity of base (NaOH) × Volume of base used (L)

Then, calculate the molarity of the unknown acid solution by dividing the moles of acid by the volume of the acid solution used (in liters). Remember to convert mL to L.

Normality (N):

Normality (N) = Equivalents of acid / Volume of acid solution (L)

An equivalent is the number of moles of H+ ions (or OH- ions for a base) that can be donated or accepted in a reaction. For a monoprotic acid, normality equals molarity.

To determine the equivalents of acid:

Equivalents of acid = Molarity of base (NaOH) × Volume of base used (L) × Number of equivalents per mole of acid

The number of equivalents per mole of acid depends on the number of acidic protons it can donate (e.g., 1 for HCl, 2 for H2SO4).

Calculate the normality of the unknown acid solution by dividing the equivalents of acid by the volume of the acid solution used (in liters).

Significance:

This experiment demonstrates the relationship between molarity and normality in titration and provides a practical method for determining the concentration of an unknown acid solution. Molarity and normality are crucial concepts in chemistry for expressing solution concentrations and calculating the amount of substance in a given volume. Understanding these concepts is essential for accurate titrations and other quantitative chemical analyses.

Share on: