Separating a heterogeneous mixture

Challenge students to separate the components of a heterogeneous mixture (marbles, gravel, sand, potting soi/vermiculite) using a variety of tools (sieve, magnets, filter paper and water).
Science content
Chemistry: Physical Changes, Solutions, Mixtures and Separating (2, 4, 5, 6)
  • small pot containing a mixture of materials:
  • 6 marbles
  • 2 Tbspns gravel
  • 2 Tbspns sand (e.g. sieved beach sand to remove shells and plants)
  • 2 Tbspns potting soil (sieved to remove plant materials), or vermiculite/styrofoam balls
  • tools to separate the materials:
  • tall tubs e.g yogurt tub
  • sieve
  • filter papers and elastic band to secure over tub
  • magnets
  • bottle of water
  • large tray to work in and contain mess
  • little cups to put separated materials into

Tell students they will separate a mixture of materials from the mixture in the pot. They will separate the marbles from the gravel from the sand from the magnetic sand from the soil/vermiculite/styrofoam balls, as best as they can, and add each separated material to its own little cup. Tell them that there are many routes to separating each of the materials out.
Show them how to use the sieve, and how to use the elastic band to secure the filter paper over the tall tub.
Students should work in a tray to contain any mess.

As students work, name the methods of separation and write up on the board as they occur:
handpicking (picking one material from a mix to separate it out)
sieving (using a sieve which catches larger materials while allowing smaller materials to pass through it)
filtration (using a filter to catch materials that are too large to pass through the filter, while allowing the liquid to flow through)
magnetic separation (using a magnet to pick up and separate out materials that are attracted to a magnet i.e. they contain iron)
sedimentation (adding materials to water to separate those that sink)
flotation (adding materials to water to separate those that float)

Circulate to encourage students to try different methods to separate out materials in their mix into different little cups.
Do not require the separation to be perfect, but that students try the different separation tools.

Once they have all separated as best they can, review the separation methods that have been written up on the board.
Add in other local processes that use any of these methods e.g. cranberries are harvested in the Lower Mainland by floation e.g. Pacific Northwest Indigenous oolichan grease prepared by flotation e.g. Pacific Northwest Indigenous clam baskets and the sustainable gill nets are sieving/filtration methods.

Other kinds of separation:
Separate seeds from a plant (faster than handpicking) by threshing (shake in bag), then winnowing (blow off lighter parts).
Separate materials of different densities by swirling and shaking in a wide pan, called yandying by Indigenous Australian cultures, also how gold panning works.

Grades taught
Gr 6