1.1.2 - Mixtures

What is a mixture? Does it have the same chemical properties as its constituent materials?

It consists of two or more elements or compounds not chemically combined together; it does have the same chemical properties.

What are the five methods through which mixtures can be separated? Do these involve chemical reactions?

• Filtration, crystallization, simple distillation, fractional distillation, & chromatography.

• They do not involve chemical reactions.

Describe and explain simple distillation.

• Used to separate liquid from a solution - the liquid boils off and condenses in the condenser.

• The thermometer will read the boiling point of the pure liquid. Contrary to evaporation, we get to keep the liquid.

Describe and explain evaporation.

• Evaporation is a technique for separation of a solid dissolved in a solvent from a solvent (e.g. salt from H₂O)

• The solution is heated until all the solvent evaporates; the solid stays in the vessel.

Describe and explain crystallization.

• Similar to evaporation, but we only remove some of the solvent by evaporation to form a saturated solution (the one where no more solid can be dissolved).

• Then, we cool down the solution. As we do it, the solid starts to crystallize, as it becomes less soluble at lower temperatures.

• The crystals can be collected and separated from the solvent via filtration.

Describe and explain fractional distillation.

• Fractional distillation is a technique for separation of a mixture of liquids. It works when liquids have different boiling points.

• The apparatus is similar to the one of simple distillation apparatus, with the additional fractionating column placed on top of the heated flask.

• The fractionating column contains glass beads. It helps to separate the compounds.

• In industry, mixtures are repeatedly condensed and vaporized. The column is hot at the bottom and cold at the top. The liquids will condense at different heights of the column.

Describe and explain filtration.

• Used to separate an insoluble solid suspended in a liquid.

• The insoluble solid (called a residue) gets caught in the filter paper, because the particles are too big to fit through the holes in the paper.

• The filtrate is the substance that comes through the filter paper.

• Apparatus: filter paper + funnel

Describe and explain chromatography.

• Used to separate a mixture of substances dissolved in a solvent.

• In paper chromatography, we place a piece of paper with a spot containing a mixture in a beaker with some solvent. The bottom of the paper has to be in contact with the solvent.

• The solvent level will slowly start to rise, thus separating the spot (mixture) into a few spots (components).

What is a separating funnel?

• An apparatus for separating immiscible liquids.

• Two immiscible liquids of different densities will form two distinct layers in the separatory funnel.

• We can run off the bottom layer (the liquid with greater density) to a separate vessel.