Mixtures often need to be separated into the substances that make them up. Being able to separate insoluble substances from each other is important to many organisms. For example, humans have kidneys that filter our blood of impurities. Grey whales scoop up sand from the sea floor and filter out their food through structures called baleen.
Magnetic separation
Your recycle bin at home contains a mixture of insoluble solids. It probably contains steel cans, glass jars, aluminium cans, paper, cardboard, plastic bottles and packaging. After collection, this mixture needs to be separated so that the different substances can be recycled and then re-used.
Magnets are convenient way of separating any rubbish made of iron, nickel and cobalt. Magnets do not attract other metals such as aluminium, copper or gold or substances such as plastic, paper or glass. Magnetic attraction allows iron and steel to be easily removed from piles of rubbish, leaving the non magnetic material behind. Magnetic separation is also used in the mining industry and in the scrap metal business.
Gravity separation
Not all mixtures contain a collection of solids like those in your recycle bin. Many mixtures are suspensions which contain insoluble solids dispersed through a liquid.
Gravity separation uses gravity to separate heavier substances from a suspension. The heavier particles sink to the bottom of the container. Gold panning uses gravity separation. The heavy gold particles drop to the bottom of the pan, allowing the lighter mud and water to be poured off.
Decantation is a type of gravity separation that lets suspensions of solids or liquids seperate naturally. The top layer can then be poured or scraped off. the top layer could be a:
- Liquid, such as oil
- solid, such as plant material like leaves and twigs in soil
- liquid, if a heavy solid has settled to the bottom
Decanting is used in a kitchen to pour off cook water from vegetables in a saucepan. Sometimes sediment will collect at the bottom of a bottle of wine that has been left to stand. Pouring the bottle into a glass container (a decanter) leaves the sediment in the bottle. Decanting is used to many industries.
Sieving
A sieve is a barrier with holes in it. Small solid particles can get through, but large ones cannot. The process is called sieving. A colander is a sieve that is used in the kitchen to strain water from food. Likewise, large lumps in flour can be removed before baking by sifting the flour through a strainer, or flour sifter.
Sieves are graded to a specific size for the job they do. They are used in mining to ensure that only rocks of the correct size enter a rock crusher. They are also used to grade soil into its different-sized particles to classify the soil being studied.
Filtration
Filtration, also known as filtering is a widely used method of separating:
- solids from gases
- solids from liquids
- liquids from gases
- liquids from other liquids.
Filtration uses a filter. A filter is like a sieve in that it is a barrier with many, many small holes (often microscopic in size) in it. These holes are smaller than the particles being separated and so these particles get caught in the filter. However, smaller particles pass straight through.
Many filters are a mesh of fine fibers like cotton wool.Others include rock with fine pores (small holes) in it.
Filters are used to separate coffee grounds from filter coffee. Likewise, tea bags are a type of filter that allows water to move through them while keeping the tea leaves in the bag. The face mask shown in Figure 4.2.5 is a filter that separates dust from air. A similar filter is used in most vacuum cleaners.The filtered, clean air is then blown back into the room. Filters can also be found in air conditioners, washing machines, dryers, swimming pools, car engines, fuel systems and air cleaners.
Filters are also used in the lab. Several different methods are used, but the most common uses filter paper.
Centrifuging
A simple centrifuge shown below. It has chambers that are spun very fast around a shaft. Any tiny particles suspended in the liquid are forced to the sides and then to the bottom of each number.
A common use of a centrifuge is in the spin cycle on a washing machine, in which the clothes are spun very fast bowl. The below figure shows how this works:
Water is forced out of the clothes and through the holes in the bowl. It then drains away and is pumped out of the machine.
There are many others designs for centrifuges. Some very complicated ones are used in mining. Centrifuging is also widely used in laboratories.
Centrifuging blood
Blood transfusions are often needed to replace blood lost in serious accidents and during major surgery. However, sometimes the blood collected at blood banks is centrifuged instead. This is done to separate it into red and white blood cells and liquid plasma. These components are then used directly or are further separated to treat particular health conditions.
Plasma is used to treat burns patients. some other conditions don’t require plasma but instead need particular chemicals extracted from it. For example chemicals called clotting factors are extracted from plasma to treat people who have haemophilia. patients with this disease can bleed to death because their blood does not clot to seal a cut.
Patients with anaemia have insufficient red blood cells in their blood. They can be given whole unseparated blood but this can stress their heart if they also have heart problems. Instead, they are given transfusions of red blood cells because these place less stress on the heart.
Unit review 4.2
Answers:
- filtering – tea bags, vacuum cleaners, air conditioners, washing machines Sieving- paster strainers, flour sifter
- Using an washing machine
- a) magnetic separation, decantation, sieving b) gravity separation, decantation, filtration c) decantation, filtration, centrifuging
- The rubbish in moving on the conveyor belt then moves onto the magnetic drum whilst the drum is rotating. The magnetic material sticks to the magnetic drum then at the end it realises the magnetic rubbish into its on bin. While the non magnetic material wouldn’t stick to the magnetic drum which makes it drop off into a different bin.
- The gold particles fall to the bottom of the container because its heavier than the mud and water is lighter so it pours out.
- a) If you magnify a paper filter there’s a bunch of fibres with spaces in between them b) A filter is like a sieve its a barrier with many, many small holes. The holes are smaller than particles so the particles get caught in the filter.
- The filter paper have really small holes, which only some particles can go through. Sugar can go through the holes which make it unable to be separated from the water.
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- a) Sieving b) Magnetic separation c) Sieving d) Sieving e) Sieving
- Gravity separation vs centrifugation
Similarities:
- they both separate the water from the solid
Differences:
- For centrifuging it has a chamber however in gravity separation it has an container
- For centrifuging the chamber are being spun however in gravity separation it just pours out the liquid
- Filtering vs sieving
Similarities:
- Both of them use can separate liquid from a solid
- Both of them have small holes that allows small particles to pass threw
Differences:
- for sieving you can separate solid from another solid however with filtering you can’t
- for filtering you can separate a liquid form another liquid however for sieving you can’t
- Folding filter paper
Conical fold (simple fold)
Pros:
- strong and thantle fluted fold and is less likely to break when moving
Cons:
- filtration rate is slow because of less surface area and thicker walls
- solution has to be poured slowly or a block might occur
Fluted fold
Pros:
- filtration speed is higher
- prevents the holes in the paper form getting blocked
Cons:
- the thinner walls make this fold more fragile
- a) more particle’s can be filtered through in less time, do like the fluted filter paper it has a higher filtration rate
b) cars on the road produce carbon dioxide, carbon monoxide and other toxic particles from their exhausts it would be incredibly unhealthy to breath car air filters are used to filter these particles out.