Introduction

Gravimetric analysis stands as one of the fundamental quantitative analytical techniques in chemistry, used to determine the mass and concentration of specific chemical substances (analytes) in a sample. This method relies on the precise measurement of mass changes during chemical reactions and is particularly valuable in analyzing inorganic compounds.

Types of Gravimetric Analysis

1. Precipitation Gravimetric Analysis

Precipitation gravimetric analysis involves converting the analyte into an insoluble precipitate that can be filtered, dried, and weighed. The process follows these essential steps:

Example: Analysis of Sulfate in Fertilizer

Consider the analysis of calcium sulfate (CaSO₄) in fertilizer using barium nitrate as the precipitating agent:

The reaction proceeds according to:

${CaSO4(aq) + Ba(NO3)2(aq) -> BaSO4(s) + Ca(NO3)2(aq)}$

For a sample calculation with:

The percentage of CaSO₄ can be calculated:

$n(BaSO_4) = \frac{0.6168}{233.37} = 0.002643 \text{ mol}$

$n(CaSO_4) = 0.002643 \text{ mol}$

$m(CaSO_4) = 0.002643 \times 136.14 = 0.3598 \text{ g}$

$\text{Mass percentage} = \frac{0.3598}{0.4550} \times 100 = 79.08\%$

2. Volatilization Gravimetric Analysis

This technique quantifies the analyte by measuring mass loss when a volatile component is released through heating or chemical reaction.

Example: Analysis of Sodium Bicarbonate

The decomposition of sodium bicarbonate in excess acid follows the equation:

${2NaHCO3(aq) + H2SO4(aq) -> 2CO2(g) + 2H2O(l) + Na2SO4(aq)}$

For a 1.00 g sample with mass loss of 0.260 g:

$n(CO_2) = \frac{0.260}{44.01} = 5.91 \times 10^{-3} \text{ mol}$

$n(NaHCO_3) = 5.91 \times 10^{-3} \text{ mol}$

$m(NaHCO_3) = 5.91 \times 10^{-3} \times 84.01 = 0.496 \text{ g}$

$\text{Mass percentage} = \frac{0.496}{1.00} \times 100 = 49.6\%$

Key Considerations