What is gravimetric analysis?

Short Answer

Gravimetric analysis is a method in chemistry used to determine the amount of a substance by measuring its mass. In this technique, the substance is converted into a solid product, which is then filtered, dried, and weighed. The mass of this solid helps calculate the amount of the original substance.

Gravimetric analysis is very accurate and is used in laboratories, industries, and environmental testing to find the amount of metals, salts, pollutants, and other chemical components with high precision.

Detailed Explanation

Gravimetric Analysis

Gravimetric analysis is a classical quantitative analytical method that determines the amount of an analyte (the substance being measured) based on its mass. It involves converting the analyte into a pure, stable compound whose mass can be measured accurately. Because mass measurement is highly reliable, gravimetric analysis provides extremely precise results when performed correctly.

This method has been used for centuries and remains important today because it requires simple equipment, is inexpensive, and offers high accuracy. Even modern instrumental methods cannot replace gravimetric analysis in certain situations.

Principle of gravimetric analysis

The principle behind gravimetric analysis is based on the idea that the mass of a substance can be used to determine its amount chemically. The analyte is first separated from the mixture and then converted into a measurable form.

The two main steps are:

  1. Separation of the analyte from the mixture
  2. Weighing of the isolated compound

From the mass of the final product, the amount of the original analyte is calculated using stoichiometry.

Types of gravimetric analysis

Gravimetric analysis can be classified into different types based on the method of isolating and measuring the analyte.

  1. Precipitation gravimetry

This is the most common type.
The analyte is converted into an insoluble solid (precipitate).
Steps include:

  • Adding a reagent that reacts with the analyte
  • Forming a solid precipitate
  • Filtering and washing the precipitate
  • Drying or heating (igniting) it to a constant mass
  • Weighing the solid

Example: Determining chloride ions by precipitating them as silver chloride (AgCl).

  1. Volatilization gravimetry

In this method, the analyte is converted into a gas that escapes. The amount lost in mass indicates the amount of analyte.

Example: Determining water content in a hydrate by heating and measuring mass loss.

  1. Electrogravimetry

Here, the analyte is deposited on an electrode by using electricity. The increase in mass of the electrode shows how much analyte was deposited.

Example: Determining copper by depositing it on a platinum electrode.

  1. Thermogravimetry

The mass of a substance is measured continuously as it is heated.
This provides information about decomposition, oxidation, or loss of water.

Steps in gravimetric analysis

Gravimetric analysis involves several carefully controlled steps:

  1. Sample preparation

The sample is dissolved in a suitable solvent.

  1. Precipitation

A reagent is added so the analyte forms an insoluble compound.
The precipitate should be pure, large, and easy to filter.

  1. Digestion

The precipitate is heated in the solution to make the particles larger and purer.

  1. Filtration

The solid is separated using filter paper or a crucible.

  1. Washing

The precipitate is washed to remove impurities.

  1. Drying or Ignition

The solid is heated to remove water or convert it into a stable form.

  1. Weighing

The mass is measured accurately using an analytical balance.

  1. Calculations

Using stoichiometry, the mass of the analyte is determined from the mass of the product.

Advantages of gravimetric analysis

Gravimetric analysis remains important because it has several strengths:

  • High accuracy (mass measurements are very precise)
  • Simple equipment required
  • No need for expensive instruments
  • Useful for standardizing solutions
  • Reliable even for complex samples

It is especially effective when high purity is required.

Limitations

Although useful, gravimetric analysis also has limitations:

  • Time-consuming
  • Requires careful handling
  • Precipitate must be pure and stable
  • Cannot be used for analytes that do not form solid compounds

Despite these drawbacks, it remains a powerful technique in classical chemistry.

Applications of gravimetric analysis

Gravimetric analysis is used in many fields:

  1. Environmental testing

Determining pollutants such as sulphates, phosphates, or metals in water.

  1. Mining and metallurgy

Determining metal content in ores.

  1. Pharmaceuticals

Analysing purity of drug samples.

  1. Food and agriculture

Measuring mineral content like calcium or iron.

  1. Analytical chemistry laboratories

Used in teaching, standardization, and research.

Example of gravimetric analysis

To determine the amount of chloride in a sample:

  1. The sample is dissolved in water.
  2. Silver nitrate solution is added.
  3. Chloride ions form a white precipitate of AgCl.
  4. The precipitate is filtered, dried, and weighed.
  5. From the mass of AgCl, the mass of chloride is calculated.

This simple and accurate method demonstrates the core idea behind gravimetric analysis.

Conclusion

Gravimetric analysis is a quantitative analytical technique that determines the amount of a substance by measuring its mass. By converting the analyte into a stable, weighable form, chemists can obtain highly accurate results. Despite being an older method, it remains widely used in laboratories, industries, and environmental monitoring because of its precision, reliability, and simplicity. Understanding gravimetric analysis is essential for mastering basic analytical chemistry.