Mixtures Jigsaw

Separation Techniques for Mixtures A mixture is a combination of two or more substances that are not chemically joined. Examples of mixtures include ice cubes in a glass of fizzy drink, sand in water, cereal in milk, oil and vinegar. Mixtures can be separated into their individual components using each component’s physical properties. The first method of separating mixtures that we will look at is decanting. Decanting a mixture involves pouring off the liquid portion of a mixture to leave only the solid behind. An example of this is if you have sand and water, you can let the sand settle to the bottom of the beaker and simply pour off the water.

Filtration is another technique used to separate mixtures. Filtering involves separating solids and liquids based on their particle size. An example of this could be when separating the pulp from a mixture of orange juice with it’s pulp. You can line a funnel with filter paper (thin paper with very small holes in it), and simply pour the mixture through the funnel. The larger pieces of pulp will not be able to pass through the filter paper , while the juice can filter through. Centrifuging involves separating objects by their density. The mixture is poured into a test tube and secured with a lid. It is then put into a machine that spins it around very quickly – very much like ‘The Invader’ at Rainbow’s End. The more dense (‘heavier’) component of the mixture will very quickly sink to the bottom of the test tube, while the less dense component stay at the top. This is often used for blood after a blood test so that the plasma and the red blood cells can be separated. Separating mixtures by evaporation involves heating the mixture up and separating the components based on their boiling points. One part of the mixture will have a lower boiling point, and will change from a liquid to a gas first. This can be evaporated off, leaving the component with the higher boiling point behind. An example of this is with salt water. The water can be evaporated off while the salt remains behind, due to salt having a much higher boiling point (1,465 °C) than water (100°C). Distillation involves evaporation where a component of the mixture is removed by turning it into a gas when it reaches it’s boiling point. However, distillation involves collecting the boiled off gas again. This is done by condensing the gas back into a liquid. We do this by passing the gas through a cool tube where it can change state back into a liquid that can be collected again.

Chromatography is a technique that separates compounds based on the size of the soluble particles in a mixture. ‘Chroma’ means colour in Greek so this is the separation based on the colour of the compounds. A small amount of the mixture is placed onto a piece of special paper, and the paper is placed into a solvent. The solvent travels up the filter paper and carries with it the different colours. More soluble (easily dissolved) pigments (colours) are carried faster up the filter paper (see diagram). Chromatography is used to separate the different colours from pens or dyes. Chromatography is used in airports to detect components of bombs too. It can also be used in forensic science where different inks or dyes can be matched to samples based on their solubilities. The last separation technique that we will look at is magnetic separation. This process separates components out of a mixture based on their magnetic properties. An example of this is separating iron from a mixture of iron and sand, or iron and other non-magnetic rocks when it is being mined. A magnet is used, and attracts magnetic components (such as iron) and leaves behind non-magnetic components.