Experimental Chemistry and Separation: notes

Apparatus and Purity

• Measuring cylinder: measures liquid volume. Read the bottom of the meniscus at eye level.
• Balance: measures mass in grams. Zero it before weighing.
• Pure substance: one substance only, with a sharp melting point and boiling point. Distilled water boils at 100 degrees Celsius.
• Impure substance: a mixture. Impurities lower the melting point, raise the boiling point and widen the melting range.

Separation Methods

• Filtration: separates an insoluble solid from a liquid, such as sand from water.
• Evaporation: removes the solvent to leave the dissolved solid. Heating salt solution leaves salt.
• Crystallisation: cooling a hot saturated solution so crystals form, such as copper sulfate.
• Distillation: separates a solvent from a solution by boiling and condensing. Pure water is collected from salty water.
• Fractional distillation: separates liquids with different boiling points using a fractionating column, such as ethanol and water.
• Chromatography: separates substances by how far they travel on paper. Rf = distance moved by spot divided by distance moved by solvent. A spot moving 3 cm while the solvent moves 6 cm gives Rf 0.5.

Tests for Gases and Ions

• Hydrogen: a lit splint gives a squeaky pop.
• Oxygen: a glowing splint relights.
• Carbon dioxide: limewater turns milky.
• Ammonia: damp red litmus turns blue.
• Chloride ions: silver nitrate gives a white precipitate.