1. Grade 7 Science: Pure Substances and Mixtures S. Willis
Separating Mixtures
Grade 7 Science: Pure Substances and Mixtures
S. Willis

2. Separating Mixtures
Key Question: How can we separate the components of a mechanical mixtures or solution?

3. Learning Goals/Success Criteria
I can describe the processes used to separate mixtures into their components and identify some industry applications of these processes.
Key terms: Sorting, floating, settling, sieve, sieving, filter, filtration, sewage

4. Separating Mixtures
Kalia always picks the tomatoes out of her salad.
Ali sorts the laundry before washing.
Jen boils pasta in water for lunch. When it is cooked she drains it through a colander.
All of these are examples of separating mechanical mixtures.

5. Sorting Mechanical Mixtures
There are 5 main ways of separating mechanical mixtures:
Sorting
Floating and Settling
Using a Magnet
Using Sieves and Filters
Dissolving Soluble Components

6. Sorting
Definition:
Physically separating large pieces of mechanical mixture so that similar pieces are together

7. Floating and Settling
Floating: a separation technique in which a “lighter” component rises to the top of a liquid where it can be skimmed or poured off.

8. Floating and Settling
Settling: a separation technique in which a “heavier” component sinks to the bottom of a liquid and the liquid can be poured off.

9. Floating and Settling
This technique is use to separate blood which is very helpful for doctors. A centrifuge is used to spin the blood samples to speed up the process of settling.

10. Floating and Settling

11. Using Sieves and Filters
Sieve: a device used to separate a mixture, with many visible holes that allow smaller solid pieces and liquids to pass through while blocking larger solid pieces.
(Verb: Sieving)
A colander is a household sieve.

12. Using Sieves and Filters
Filter: a device with many small holes or channels that can be used to separate a mixture. Filtration removes tiny pieces of solids from a liquid or a gas. The holes are much smaller than a sieve.

13. Using a Magnet
Some metals and alloys, such as iron and steel, are attracted to magnets. If only one part of a mixture is attracted magnets, a magnet can be used to separate that part from the rest of the mixture.

14. Dissolving Soluble Components
If one part of a mechanical mixture dissolves easily in a solvent, you can separate this mixture using dissolving.
What would happen if you pour a mixture of salt and sand in to a glass of water?

15. Applying Separating Mixtures to the Environment
Think about the last time you visited a lake or river. Did it look and smell clean? Often water around cities is polluted. There are two ways that cities deal with this:
1. Try to stop or limit pollution from sources.
2. Treat any water that contains pollutants, such as waste from sinks and toilets, before it reaches the lakes and rivers.

16. Sewage Treatment
Sewage: the mixture of water and waste that is flushed down toilets and sink drains.

17. Sewage Treatment
Primary Treatment: half of the solids in sewage are removed from the mixture through sieving, then settling.

18. Sewage Treatment
Secondary Treatment: The remaining dirty water passes through tanks containing bacteria that break down any remaining human waste and plant material. Then the water is allowed to settle again. The bacteria settles and is removed.

19. Sewage Treatment
Tertiary Treatment: Pollutants like phosphorus and nitrogen (from soaps) are removed by bacteria that is encouraged to grow by ultraviolet or ozone exposure. Chlorine kills any remaining organisms.

20. Sewage Treatment

21. Keeping our Water Clean
Mixtures of dirty water can be very difficult to separate. Some of the contaminants include:
Waste produced by factories
Fertilizers, pesticides or salt from farms, golf courses or roads
Accidental spills and leaks (think oil spills from ships)
Video: Sewage Treatment Process