Essential Definitions in Solution Chemistry and Titration

Normality (N)

Normality expresses the equivalent number of grams of solute present in one liter of solution.

Calculating the Equivalent Gram (Eq)

The equivalent gram is crucial for calculating normality. Its determination depends on the nature of the substance:

Equivalent Gram for Acids

To determine the equivalent gram of an acid, divide the gram molecular mass by the number of replaceable hydrogen atoms (H+).

Equivalent Gram for Bases or Hydroxides

To determine the gram equivalent of a base or hydroxide, divide the gram molecular mass by the number of hydroxyl groups (OH-) present.

Equivalent Gram for Salts

To determine the equivalent gram of a salt, divide the gram molecular mass by the total positive valence of the metal cation.

Molality (m)

Molality is the number of moles of solute dissolved in 1 kg (1000 g) of solvent. A molal solution is one that contains one mole of solute dissolved in 1 kg of solvent.

Mole Fraction (X)

This unit refers to the fraction of each component in a solution. It is calculated by dividing the number of moles of a specific component by the total number of moles in the solution.

Titration (Volumetric Analysis)

Titration is a procedure involving the careful addition of a precisely measured amount of a reagent (the titrant) to a solution containing the analyte. The goal is often to achieve a color change in a third substance, called an indicator, which signals that the chemical reaction has been completed (the equivalence point).

Acidimetry and Alkalimetry

These two are specific variants of titration procedures:

Acidimetry

Acidimetry is the assessment (titration) of acids using standard alkaline solutions (bases or hydroxides).

Alkalimetry

Alkalimetry is the reverse process: the assessment (titration) of bases using standard acid solutions.

Neutralization Reactions

When an acid and a base are in contact, a double decomposition reaction takes place, known as neutralization. This reaction produces a salt and water.

Fundamental Principle of Neutralization

The fundamental principle underlying the neutralization reaction is that one gram equivalent of an acid always combines with one gram equivalent of a base, and vice versa.

Chemical Indicators

Indicators are substances characterized by changing color depending on the pH of the medium they are in. Their main requirements for use include being colorless in the medium to avoid color interference and possessing sufficient optical clarity to allow appreciation of the color changes.

Common Indicators

• Methyl Blue
• Bromothymol Blue
• Methyl Red
• Phenolphthalein

Colligative Properties of Solutions

The properties of solutions that depend solely on the number of solute particles present, and not on the nature of these particles, are called colligative properties. These properties are highly useful for determining the molecular mass of an unknown solute.

Key Colligative Properties

• Vapor Pressure Lowering
• Boiling Point Elevation
• Freezing Point Depression
• Osmotic Pressure

Vapor Pressure

Vapor pressure refers to the force exerted by the gas molecules of a material on the surface of that material when the system is in equilibrium.