What is Gravimetric Analysis? | Chemistry for EmSAT Achieve PDF Download

Introduction

Gravimetric analysis is an analytical chemistry technique used to determine the quantity of a substance (analyte) based on the measurement of its mass in the form of a solid. For instance, one application of gravimetric analysis involves measuring the amount of suspended solids in a water sample. After filtering a known volume of water, the collected solids are weighed to determine their mass.

The Principle of Gravimetric Analysis:

The underlying principle of gravimetric analysis is that the mass of a specific ion can be determined in a pure compound. This mass measurement is then used to calculate the mass percentage of the same ion in a known quantity of an impure compound.

Steps in Gravimetric Analysis

• Preparation of a solution containing a known weight of the sample.
• Separation of the desired constituent.
• Weighing the isolated constituent.
• Calculation of the amount of the specific constituent in the sample based on the observed weight of the isolated substance.

Types of Gravimetric Analysis

There are four fundamental types of gravimetric analysis, two of which involve changes in the phase of the analyte to separate it from the rest of the mixture, resulting in a change in mass.

• Volatilization gravimetry: Involves separating components of a mixture by heating or chemically decomposing the sample.
• Precipitation gravimetry: Uses a precipitation reaction to separate one or more components of a solution by incorporating them into a solid.
• Electrogravimetry: A method used to separate and quantify ions of a substance, typically metals.
• Thermogravimetry: A method of thermal analysis that measures changes in the physical and chemical properties of materials as a function of increasing temperature or time.

Advantages of Gravimetric Analysis

• Provides highly precise analysis when the methods are followed carefully.
• Used to determine the atomic masses of many elements with high accuracy.
• Minimizes instrumental errors and does not require a series of standards for calculating unknown samples.

Disadvantages of Gravimetric Analysis

• Typically limited to analyzing a single element or a specific group of elements at a time.
• Comparing it to modern techniques like dynamic flash combustion coupled with gas chromatography, traditional combustion analysis may have limitations.

Example

An ore is analysed for the manganese content by converting the manganese to Mn₃O₄ and weighing it. If a 1.52g sample yields Mn₃O₄ weighing 0.126g, what would be the percent Mn₃O₃ in the sample? The percent of Mn?

Mn₃O₄ consists of Mn₂O₃ and MnO

All the manganese in the ore is converted into Mn₃O₄

Amount of Mn in Mn₃O₄ = (0.126/2.29) × (3 × 55)

= 0.091 g

% of Mn in the ore = (0.091/1.52 ) × 100

= 5.973 %

% ofMn₂O₃ = [0.126g Mn₃O₄ × (3 Mn₂O₃ / 3 Mn₃O₄) (Mn₂O₃ / Mn₃O₄ ) × 100 ]/ 1.52g sample

= 8.58 %

%Mn = [0.126g Mn₃O₄ × (3 Mn /Mn₃O₄) (gMn/Mn₃O₄) × 100] / 1.52g sample

={0.126g×[3(54.94)/228.8]1.52g}×100%

=5.97%