Eudiometry (Gas Analysis) | Basic Concepts of Chemistry Class 11

Eudiometry (Gas Analysis)

Stoichiometry of Gaseous Reactions | Basic Concepts of Chemistry

1. What is Eudiometry?

Eudiometry is the process of determining the molecular formula of gaseous hydrocarbons or investigating the composition of gaseous mixtures by measuring volume changes during combustion or absorption.

                    Principle (Avogadro's Law): At constant temperature and pressure, volume is directly proportional to the number of moles.
                    $$ V \propto n $$
                    Therefore, we can use Volumes directly in stoichiometric calculations instead of moles.
                

2. General Combustion Equations

For a hydrocarbon $C_xH_y$ or an organic compound $C_xH_yO_z$, combustion follows these equations:

Hydrocarbon ($C_xH_y$):
$$ C_xH_y + (x + y/4)O_2 \rightarrow xCO_2 + y/2H_2O(l) $$

Organic Compound ($C_xH_yO_z$):
$$ C_xH_yO_z + (x + y/4 - z/2)O_2 \rightarrow xCO_2 + y/2H_2O(l) $$

Note on Water: At room temperature, water produced is in liquid state, so its volume is considered negligible (zero) compared to gases. Above $100^\circ C$, it is a gas (steam).

3. Volume Contraction

Combustion usually leads to a change in volume. The contraction is calculated as:

$$ \text{Volume Contraction} = V_{reactants} - V_{products} $$

For $C_xH_y$: Contraction = $V_{HC} + V_{O_2} - V_{CO_2}$ (ignoring $H_2O(l)$).

4. Common Gas Absorbents

To analyze a mixture, specific reagents are used to absorb specific gases, reducing the total volume.

Gas	Absorbent Reagent
$CO_2, SO_2, Cl_2$ (Acidic gases)	$KOH$ / $NaOH$ solution
$O_2$ (Oxygen)	Alkaline Pyrogallol
$O_3$ (Ozone)	Turpentine Oil
$CO$ (Carbon Monoxide)	Ammoniacal $Cu_2Cl_2$
$H_2O$ (Moisture)	Anhydrous $CaCl_2$ or $P_4O_{10}$
$NH_3, HCl$	Water (highly soluble)

Practice Quiz

Test your logic on Gas Analysis.

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