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Activity

Making mixtures

Summary: 
Shake water with various solids, to discover different kinds of mixtures - suspensions, colloids and solutions
Science content (2016 curriculum): 
Chemistry: States of Matter, Properties of Materials (K-7)
Chemistry: Atoms, Molecules (3-7)
Chemistry: Physical Changes, Solutions, Mixtures and Separating (2, 4, 5, 6)
Lessons activity is in: 
Materials: 
  • squeeze bottle of water
  • little clear pots with sealable lid
  • materials to shake with the water that will make different kinds of mixtures e.g. flour, baking soda, sugar, sand, milk, coloured drink syrup
  • waste tub for further free experimentation
Procedure: 

Students start by mixing each of the materials in turn with water. They add a thin layer of each material to the bottom of the pot, then top up with water. Shake hard for 10 seconds or so. Then leave it undisturbed. They can pick it up to look closely, but don’t shake it again.
They assess whether they can see through the mixture (when it is shaken up), then if the material settles out again.
They can use the attached worksheet to determine what kinds of mixtures are made in each case. In summary:
A suspension has clumps of one material in another (e.g. particles of sand or flour in water). This kind of mixture does not let light pass through it i.e. you cannot see through it. The solid clumps do settle out, even if they take some time, as they are large enough for gravity to pull them down.
A colloid has smaller clumps of material in another (e.g. milk in water is clumps of liquid fat floating in a watery liquid). A colloid does not let light pass through. It does not settle out, as the clumps are too small to be pulled down by gravity.
A solution is clear - you can see through it (even if it is coloured). It does not settle out. In a solution the particles of one material are completely evenly distributed amongst the particles of the other material. Their molecules are evenly mixed, and behave as one phase of matter.

To see the particles in a colloid, look at milk under a transmission scope at 40X or higher.

Relate to familiar mixtures:
suspension - silt in a river are deposited. sedimentation used for water treatment (particles coagulated first), then filtration to separate more particles.
colloid - milk. other oil in water - salad dressing.
solution - salt, coffee, apple juice - various molecule in solution with water

Allow free play time for students to mix the materials together as they wish, followed by discussion of what they found.

Notes: 

This is a more focused exploration of mixtures. Mixing solids and liquids is a more general discovery of mixtures and chemical reactions.

Students thought that sand made a solution as it settled out very fast to leave the clear water above. Switch to a material that does not settle out quite as fast. Finer sand? Play sand?

Trying to show light passing through, or not, add a level of complication that was not always clear.

Use milk powder instead of liquid milk? Also replace drink mix with a powder - crystal light?

Grades taught: 
Gr 4
Gr 5
Gr 6
Teacher: 
Gretchen Bartlett
Lisa Shideler
Teaching site: 
Maple Grove Elementary
Activity originally developed and delivered: 

Maple Grove Elementary