How Precipitate is Formed in Gravimetric Analysis and Explain about its Properties

The concept of gravimetric analysis is essential to determine various factors that are parts of our life, such as food nutrition, metal purity, water purity and more. There are multiple ways to scientifically measure, and analyse chemical substances, such as volumetric analysis, instrumental analysis, and gravimetric analysis.

The analysis concludes by determining the volume or weight of the substance. When expressed in weight, it’s called gravimetric analysis. 

A precipitate is a solid formation in a solution or the solid by-product of a chemical reaction within a solution.

What is Gravimetric Analysis?

This is a method where the quantity or amount of analyte is determined by measuring the mass. It relies on comparing the masses of two compounds with the same type of analyte, or it can also be explained as the difference or change in mass compared to its mass concentration. It is highly accurate as it undergoes various reactions to achieve the best results.

Conditions for gravimetric analysis

• The analyte or ion being studied must be precipitated completely, i.e., it needs to be in solid mineral form.
• The analyte precipitated must be pure.
• The precipitate must be easily filterable.

Types of gravimetric analysis

• Volatilisation

In this method of gravimetric analysis, the process of physical gravimetry separates the different components in a compound via the process of heating or decomposition chemically.

• Precipitation

In the precipitation method, the components undergo a precipitation reaction which separates part of the solution into a solid form called a precipitate. This precipitate is the analyte in solid form.

• Electrodeposition

In this process of gravimetric analysis, usually applicable in metals, a unique methodology is used to extract the analyte ions from the metal.

• Thermogravimetry

In this method of gravimetric analysis, the compound undergoes thermal analysis that accounts for the change in chemical and physical factors of the compound with increasing temperature and time.

How is a precipitate formed?

A precipitate is formed during a precipitate reaction. In this reaction, a solid compound is formed because the solution has a mix of cations and anions. This solid which is formed is the precipitate. Precipitates are usually insoluble ionic compounds of precipitate reactions. These reactions are primarily used in the gravimetric analysis.

Examples of precipitate formation in Gravimetric Analysis

• The reaction between sodium sulphate and barium chloride gives us the precipitate barium sulphate. 

Na₂SO₄ + BaCl₂ → BaSO₄ + 2 NaCl

• The reaction of boric acid in water 

Na₂B₄O₇.10H₂0 → 4H₃BO₃ + 5H₂0 + 2NaCl

Factors that affect a precipitate

The precipitate formed during the gravimetric analysis has many variables that alter or may bring about change in the precipitate. These factors are:

1. The solubility of the precipitate – this factor is essential as the solubility determines how easily the precipitate can be extracted if the precipitate is highly soluble. It is very hard and pointless to extract it from the reactant solution.

The dissolution of the precipitate in the solution will result in a loss of mass of the precipitate, resulting in the wrong weight during gravimetric analysis. Hence, the solubility of the precipitate has to be very low to get accurate results during gravimetric analysis.

2. Impurities of a precipitate – if the precipitate is formed in a solution with high-level impurity, then the probability of the precipitate also being impure is significantly high.

This is concerning as it can meddle with the results obtained during gravimetric analysis. The surface of the precipitate formed is the most likely to be impure because it is the most prone to physical and chemical interactions with other reagents. If the impurity of the precipitate is very significant, it must be reprecipitated for more pure results.

3. The particle size of a precipitate – often, the precipitate is crystalline form. These formations need to be of a specific size, as the size of the particles plays a role in their formation. If the crystals are large, they are easier to filter, whereas small crystals are harder to purify from their impurities.

Conclusion

The quantitative chemical analysis seeks to understand the composition of a given mixture. A critical method of quantitative chemical analysis is the gravimetric analysis method. A popular gravimetric analysis method that is used is precipitation gravimetric analysis.

In this, a precipitate is formed from a solution that contains the mixture, and then the dry weight of the precipitate is used to understand the composition of the mixture. There are other forms of gravimetric analysis like thermogravimetry, electrodeposition, and volatilisation.

The precipitate formed during gravimetric analysis has different factors that affect it, like its solubility, the amount of impurity present in it, and the size of the particle present in it. All these factors play a part in ensuring that the precipitate formed is immune to mass changes. The analysis made under the gravimetric analysis method is not faulty and accurate.