Lesson 3 Page 1
Explore: Separating Heterogeneous Mixtures
You will begin by looking at various methods for separating heterogeneous mixtures. Because the particles in heterogeneous mixtures are not dissolved, they are easier to separate than homogeneous mixtures. (You will consider separating homogeneous mixtures later.)
Remember that you can see the parts of a heterogeneous mixture. Depending on the properties of those parts, you can use one of the following methods for separation:
Mechanical Separation
The obvious property is the different appearance of particles.
Various particles are separated by picking apart by hand or tweezers the parts of the mixture. This works best with larger particles where the differences between them are easy to see.
Filtration
The obvious property is the different sizes of particles.
The mixture is poured through a filter through which smaller particles pass through and larger particles are caught. This works best for mixtures with a significant difference in the sizes of the particles.
Flotation
The obvious property is the ability to float, or buoyancy.
Add water to the mixture. The buoyant particles float. The heavier particles sink to the bottom. This method works only if one part of the mixture is denser than water is and the other part is less dense than water is.
Dissolving
The obvious property is solubility.
Add water to the mixture. The soluble part of the mixture dissolves, leaving the insoluble part behind. Then, this mixture can be filtered to separate the parts further. This method works best for mixtures where one part of the mixture is water soluble and the other part is water insoluble.
Magnet
The obvious property is the response to magnetism.
Use a magnet to attract and remove the magnetic parts of the mixture. This method works if the parts of the mixture have various magnetic properties. (Only one of the components can be magnetic.)
What methods can be used for separating heterogeneous mixtures?
- water
- jar or bowl
- toothpicks
- fine sand
- paper clips
- iron filings (optional)
- magnet
- salt
- marbles
- coffee filters
- sieve or colander
Check Your Answers
Once you have completed this activity, check your answers below.
Mixture |
Separation Method |
How and why did your method work? |
| 1 handful paperclips and 1 handful of marbles |
- mechanical separation
- magnetism - flotation |
- The difference between the marbles and paperclips is seen easily.
- Paperclips are magnetic; marbles are not. - Paperclips float on the water; marbles will not. |
| 1 spoonful salt and 1 spoonful pepper | - dissolving | - The salt is soluble in water and dissolves, leaving the pepper behind |
| 1 spoonful sand and 1/4 cup water | - filtration | - The water passes through the coffee filter. The sand is too big to pass through and is caught in the filter. |
| 1 handful marbles and 1/4 cup water |
- mechanical separation
- filtration |
- The marbles are large and easy to remove from the water by hand.
The marbles are large and are caught in the sieve or colander as the water passes through it. |
| 1 pinch of iron shavings and 1 spoonful salt |
- magnet
- dissolving |
- The iron shavings are magnetic while the salt is not.
- The salt is soluble in water and dissolves while the iron shavings will be left behind. |
| 1 handful of paperclips and 1 handful of toothpicks |
- mechanical separation
- magnet |
- The various parts are large enough and easy to pick apart by hand.
- The paperclips are magnetic while the toothpicks are not. |
| 1 handful of toothpicks and 1 handful of sand |
- mechanical separation
- filtration |
- The parts have different shapes. Picking out the toothpicks is easy by hand.
- The toothpicks are large and are caught in the sieve/colander while the fine sand passes through. |
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Which of your hypotheses did not work? Explain.
Answers will vary.
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Mechanical separation can be used for many of the mixtures you made. Explain why you might choose another method instead of mechanical separation.
Mechanical separation takes more time and effort. Other methods can separate the mixtures more quickly and effectively.
- Based on your observations, complete the following chart to answer your Explore Question: What methods can be used for separating heterogeneous mixtures?
| Mixtures that have parts that are… | can be separated by… |
| Various sizes | mechanical separation/filtration |
| various magnetic properties | magnetism |
| various solubility in water | dissolving |
| various densities (and buoyancy in water) | flotation |
Science Connection
Iron is an important mineral that our bodies need to keep us healthy. Many breakfast cereals are fortified with iron to ensure we get enough iron in our diets. Because iron is magnetic, you can separate the iron from the cereal by using a strong magnet.
See how it is done in this video, and you can even try it at home!