Separating MixturesGrade 7 Science: Pure Substances and Mixtures

S. Willis

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

Separating Mixtures

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

Learning Goals/Success Criteria

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.

Separating Mixtures

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

Sorting Mechanical Mixtures

Sorting

Definition: Physically separating

large pieces of mechanical mixture so that similar pieces are together

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.

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.

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.

Floating and Settling

Floating and Settling

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.

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.

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.

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?

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.

Applying Separating Mixtures to the Environment

Sewage Treatment

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

Sewage Treatment

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

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.

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.

Sewage Treatment

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

Keeping our Water Clean