Chemistry - Experimental Techniques and Chemical Analysis

Purity of a substance can be determined by its melting point ($MP$) and boiling point ($BP$). Pure substances have a specific, sharp $MP$ and $BP$, while impurities lower the $MP$ and increase the $BP$ over a range of temperatures.

Chromatography is used to separate mixtures of soluble substances like dyes or pigments. The stationary phase is the paper, and the mobile phase is the solvent. The $R_f$ value is a ratio used to identify components.

Filtration is used to separate an insoluble solid (residue) from a liquid (filtrate).

Crystallization is used to obtain a pure solid sample from its solution by evaporating the solvent until the point of crystallization is reached.

Simple Distillation separates a liquid from a solution (e.g., obtaining $H_2O$ from sea water), while Fractional Distillation separates miscible liquids with different boiling points (e.g., separating $C_2H_5OH$ from $H_2O$).

Testing for Anions: Carbonates ($CO_3^{2-}$) react with dilute acid to produce $CO_2$ gas. Chlorides ($Cl^-$) produce a white precipitate with acidified $AgNO_3$. Sulfates ($SO_4^{2-}$) produce a white precipitate with acidified $Ba(NO_3)_2$.

Testing for Cations: Aqueous $NaOH$ or $NH_3(aq)$ is used. For example, $Cu^{2+}$ forms a light blue precipitate, while $Fe^{2+}$ forms a green precipitate and $Fe^{3+}$ forms a reddish-brown precipitate.

Gas Tests: Hydrogen ($H_2$) is tested with a lighted splint (squeaky pop); Oxygen ($O_2$) relights a glowing splint; Carbon Dioxide ($CO_2$) turns limewater ($Ca(OH)_2$) cloudy/milky; Ammonia ($NH_3$) turns damp red litmus paper blue; Chlorine ($Cl_2$) bleaches damp litmus paper.