SC.5.P.8.3 Separating Mixtures

SC.5.P.8.3: Demonstrate and explain that mixtures of solids can be separated based on observable properties of their parts such as particle size, shape, color, and magnetic attraction.

What is a Mixture?

A mixture is a combination of two or more things with different physical properties. Mixtures can easily be separated. A box of crayons is a mixture of similar objects with different colors. To separate a mixture of crayons, you would reach in with your fingers and pull out the different colors of crayons.

Some mixtures can be separated with fingers. Sometimes it is easier to use a tool to separate a mixture. For example, if the pieces of a mixture were very small, it might be easier to use tweezers or forceps. Some mixture can be separated using a magnet. A mixture of sand and metal filings is easily separated using a magnet. The particles, or pieces, of sand and magnetic filings are very similar in size, and so small it would be hard to separate them. Because metal filings are magnetic, a magnet can be used to attract the filings and leave behind the sand.

A sifter is another tool that can be used to separate a mixture. A mixture of sand and small pebbles could be separated by hand using forceps but pouring the whole mixture through a sifter easily separates the larger pebbles. The small sand particles fall right through the sifter.

How Can a Mixture Be Separated by Particle Size?

A particle is a smaller piece of something larger. When a large boulder is broken apart smaller rocks are made. The rocks are just smaller pieces of the larger boulder. Break a rock, and pebbles might be made. If pebbles are broken again, particles as small as sand are made. Sand is just smaller piece, or particle, of a larger rock.

There are several ways to separate a mixture of pebbles and sand. You could use your fingers to reach in an pull out the pebbles. You might use forceps to pull out the smaller pebbles. The quickest way to separate a mixture of fine and coarse particles is to pour it through a sifter. The fine particles of sand will fall through the sifter. The coarse pebbles will stay in the sifter.

Salt is another common material that comes in different particle sizes. The salt you are most familiar with is table salt. These are the smallest particles of salt, easy to pour from a shaker. Coarse sea salt is also common. Coarse sea salt is made of particles that are larger than table salt. Rock salt is the largest common size of salt. You might infer from the name that rock salt is about the size of rocks. These are often used in water softeners for homes.

To separate a mixture of rock, sea, and table salts, you might start by picking out the largest particles with your fingers. Rock salt is easy to separate this way. Next, you might try picking out the particles of sea salt using forceps. The quickest way to separate the particles of coarse sea salt and table salt is to pour them through a sifter. The fine particles of table salt through the sifter, leaving behind the coarse sea salt particles.

How Can a Mixture Be Separated by Magnetic Attraction?

Mixtures can be separated by magnetic attraction if one of the solids in a mixture is magnetic. Materials that are magnetic are attracted, or pulled, to a magnet. A magnet has no effect on materials that are not magnetic. Magnets will either attract (pull) or repel (push) other magnets, depending on which pole, or end, of the magnets are put together.

Recycling plants use magnets to separate iron scraps from aluminum cans. Not all metals are magnetic. Aluminum is not magnetic, so the magnet will separate the iron scraps from the aluminum cans.

Scrapyards also use magnets to separate mixtures. Very large magnets on cranes can be used to lift out large pieces of magnetic iron scrap. The non-magnetic metal scraps can then be separated into a different pile.

Metal filings are small pieces, or particles, of metal that are formed when metal objects like axes are sharpened. The small pieces of metal that are scraped from the ax are as small as sand particles. However, because they are sharp, you might want to separate the filings from the sand they fell into. Using a magnet, the metal filings are easily attracted and pulled out of the mixture.