Separation and Purification Techniques

• Separation and purification involves various techniques to isolate and purify substances from mixtures.

Separating Solid-Solid Mixtures

• Magnetic attraction separates magnetic solids from non-magnetic solids.
• Sieving separates solids of different particle sizes using a sieve with suitable pore size.
• Suitable solvents separate solid-solid mixtures when only one solid is soluble in the solvent.
• Sublimation separates substances that sublime on heating from substances stable at sublimation temperatures, e.g., naphthalene and iodine.

Separating Solid-Liquid Mixtures

• Filtration separates insoluble solids from liquids, leaving a residue (insoluble solid) on the filter paper and a filtrate (liquid) in the beaker.
• Solid particles that are too large to pass through filter paper pores get separated from th liquid.
• Evaporation to dryness separates dissolved solids from their solvent by heating until the solvent boils off; however, some solids may decompose, and impurities may remain.
• The solvent must have a lower boiling point than the dissolved solid.
• Crystallization obtains a pure solid from a saturated solution.
• Solubility increases with temperature, while crystallization increases with decreasing temperature.
• Gently heat the solution until saturated, stop heating before all of the solvent evaporates, and allow the solution to cool and crystallize.
• Filter the mixture to collect, wash the solid with cold distilled water to remove impurities, and dry it between sheets of filter paper.

Simple Distillation

• Separates a pure solvent (liquid) from a solution.
• A thermometer placed at the sidearm measures the boiling point.
• Solution is heated with boiling chips to ensure smooth boiling.
• Liquid boils into gas, enters the condenser and is condensed to a purified liquid.
• Liquid is collected as a distillate in a beaker, as more liquid vaporizes, the solution concentrates leaving a solid residue in the distillation flask.

Separating Liquid-Liquid Mixtures

• A separating funnel separates immiscible liquids that do not form a homogenous liquid when mixed.
• Separating funnel can only be used when liquids have uniform composition.

Chromatography

• Chromatography separates a mixture of substances with differing solubilities in a solvent.
• Solvents include ethanol or water.
• The flask with the chromatogram should be covered to minimize solvent loss through evaporation and improve ink separation.
• A pencil line should be used because it is insoluble in most solvents, ensuring it does not dissolve and interfere with results.
• If only one spot is seen for substance B, it is a pure substance.
• Substance D remaining on the start line indicates it is insoluble in the solvent.
• If substance A contains spots at the same height as substances B and C, A is a mixture of B and C.
• The retention factor (Rf) is the ratio between the distance traveled by the substance and the solvent.
• The Rf value is the same regardless of the distance traveled on the chromatogram if the solvent and temperature are the same.

Fractional Distillation

• Separates miscible liquids with different boiling points.
• Heating the solution causes both ethanol and water vapor to rise into the fractionating column.
• Water condenses on the cooler surfaces within the fractionating column and flows back into the flask due to its higher boiling point than ethanol.
• Ethanol vapor continues to rise, exiting the column into the condenser at its boiling point of 78°C.
• Ethanol vapor cools and condenses into a liquid (pure), which is collected as a distillate in a beaker.

Purity

• To prove if a substance is pure, check if it consists of a single element or compound (not mixed with other substances).
• Pure substances have fixed melting and boiling points.
• Impure substances have a range of melting and boiling points.
• Impurities lower the melting point of solids and increase the boiling points of liquids.

Learn about different separation and purification techniques used to isolate substances from mixtures. This includes methods for solid-solid mixtures like magnetic attraction and sieving. Also learn methods for solid-liquid mixtures like filtration and evaporation.