Mixtures What is a mixture? A mixture contains two or more chemically pure substances that can be separated easily using a physical process such as sieving or filtering.

Types of Mixtures Solution - A solution is formed when one substance (known as the solute) dissolves in another (the solvent). For example, when sugar is mixed with water, the solute is the sugar and the solvent is the water. Concentration - When a solvent (e.g. water) contains a large amount of solute (e.g. salt) the solution is said to be concentrated. The opposite of concentrated is dilute.

Concentration

Suspension - A mixture of water and sand is not a solution, but is known as a suspension. Sand in water

Colloids - A colloid is a mixture that is between a solution and a suspension. The particles in a colloid are bigger than those in a solution, but smaller that those of a suspension, and do not settle out as quickly.

Sols A sol is a colloid where particles of a solid are spread throughout a liquid. Blood plasma is an example of a sol in which solid blood proteins are spread throughout water. Blood is made up of blood plasma and blood cells. Emulsions - An emulsion is a colloid in which particles of a liquid are spread throughout another liquid. Milk, for example, is an emulsion of liquid fat spread throughout water.

Separating insoluble Mixtures Decanting - Decanting is a simple method of separation that can be used to separate suspensions. The suspension is left long enough for most of the sediment to collect at the bottom of a container. The liquid above the sediment is then carefully poured into another container.

Sieving and filtration – Sieving - Sieving is useful when there are different-sized particles in a mixture. Sieves are commonly used in the kitchen to remove lumps from flour. Likewise, a special sieve called a colander catches spaghetti while letting the hot water pass through.

Filtration - Filtration uses a very fine sieve called a filter Filtration - Filtration uses a very fine sieve called a filter. One type of filter used in the laboratory is filter paper. Filter paper contains millions of tiny holes that allow particles in a solution to pass through, but not the larger particles. These get trapped in the filter paper.

Getting particles moving Centrifuging - Another method involving the movement of particles is centrifuging. The spin drier in a washing machine is a type of centrifuge. When the spin cycle activates, the drum rotates rapidly, forcing the clothes and water against the drum wall. The walls contain small holes that allow water to pass through them and be pumped out, leaving the clothes ‘spun dry’.

http://www.youtube.com/watch?v=X1HKpzUvFlQ Magnetic separation -Magnets attract iron and steel (an alloy of iron) but do not attract other metals, such as copper, gold or aluminium. Magnets also have no effect on plastics, glass, paper or cardboard. Therefore, magnets provide an easy way of separating iron and steel from non-magnetic materials.

Froth Floatation - Froth flotation is used in the processing of minerals. During copper production, rocks containing grains of copper must first be crushed and ground to a fine powder—this is called liberation. Once liberation has occurred, the powder is mixed with water and special chemicals in flotation cells. Air is then blown into the mixture to produce bubbles of froth.

Separating Soluble Substances Evaporation and Crystallisation - A filter cannot separate the solute particles in a solution because the particles are far too small to be trapped by any filter. However, pure crystals of the solute(known as residue) will be left behind if the solvent is heated so that it evaporates and becomes a gas. Boiling the solution speeds up the evaporation process. http://www.youtube.com/watch?v=FggCU_Id_mk

Distillation - Distillation involves evaporation too, but collects the evaporated solvent instead of letting it escape into the atmosphere. The evaporated solvent is cooled and condensed back into a liquid, which is distillate. As in evaporation, what remains in the original container is known as the residue. http://www.youtube.com/watch?v=xxNfJLMNS4E

Absorption - Absorption occurs when a material is taken in by another Absorption - Absorption occurs when a material is taken in by another. A kitchen sponge, for example, absorbs water. Special chemicals can be used to absorb particular substances from a mixture.

Chromatography - Chromatography is a technique that can be used to separate colours in inks, food dyes and other mixtures of colours. A medium, such as blotting or filter paper, containing a spot of the mixture is placed in contact with a solvent (e.g. water). The different colours move throughout the medium at different rates and so are separated along it. http://www.youtube.com/watch?v=8uFLOQ18Mt8