1.1.5 Mixtures

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

  A mixture consists of two or more elements or compounds chemically combined together; it does have the same chemical properties.
• What are methods through which mixtures can be separated? (5) Do these involve chemical reactions?

  Filtration, simple distillation, fractional distillation, chromatography. These methods do not involve chemical reactions.
• Describe and Explain simple distillation.

  Simple distillation is used to separate liquid from a solution. The liquid boils off and condenses into 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 crystallisation/evaporation.

  Evaporation is a technique for separation of solid dissolved in a solvent from a solvent (e.g. salt from H20). The solution is heated until all the solvent evaporates; the solid stays in the vessel. Crystallisation is similar, but we only remove some of the solvent by evaporation to form a saturated solution (the one where no more solid can be dissolved).
• Describe and explain Crystallisation.

  Then, we cool down the solution. As we do it, the solid starts to crystallise, 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 heated flask. The fractionating column contains glass beads. It helps to separate the compounds. In industry, mixtures are repeatedly condensed and vapourised. The column is hot at the bottom and cold at the top. The liquids will condense at different heights of column.
• Describe and explain filtration.

  Filtration is used to separate an insoluble solid is suspended in a liquid. The insoluble liquid (call a residue) gets caught in a filter paper, because the particles are too big to fit through the holes in paper. The filtrate is the substance that comes through the filter paper. Apparatus: filter paper + Funnel.
• Describe and explain in chromatography.

  Chromatography is 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 will slowly start to rise, thus separating the spot (mixture) into a few spots (components).
• What is a separating funnel?

  A separatory funnel is 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.
• Explain the following: Solute, Solvent, Solution, Miscible, Immiscible, Soluble, Insoluble.

  A solute is a substance that is dissolved in a solvent. Together, they form a solution. Miscible refers to the substances (particularly liquids) that mix together, e.g. water and alcohol. Water and Oil are immiscible, i.e. they don't mix. Soluble refers to the substance that can be dissolved in a solvent, e.g. salt in water. Insoluble substance won't dissolve in a particular solvent.