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Activity

Glue

Summary: 
Make glues from household ingredients and test how long they can hold a marble to a piece of cardboard. Understand some of the ways that glues work on a molecular level.
Science content (2016 curriculum): 
Chemistry: States of Matter, Properties of Materials (K-7)
Chemistry: Physical Changes, Solutions, Mixtures and Separating (2, 4, 5, 6)
Materials: 
  • labelled containers of flour, cornstarch, milk powder, icing sugar
  • small scoops e.g. 1/8 teaspoon measures, or use coffee stir sticks broken in half
  • squeeze bottle of water
  • stir sticks e.g. wooden coffee sticks
  • trays with small compartments e.g. paint trays or ice cube trays
  • optional: worksheet (see attached)
  • marbles
  • strips of cardboard e.g. cut up cereal box
  • waste tub
Procedure: 

This activity adapted from https://www.acs.org/content/dam/acsorg/education/resources/k-8/science-a...

Give students tubs of glue making materials, scoops, water bottles, trays, stir sticks.
Ask them to make the best glue possible, mixing the ingredients in a well of the tray. They should test their glue by putting a blob of it on a cardboard strip, pushing a marble into it, then hanging the strip upside down - the longer the marble holds, the better the glue. A long-lasting recipe can be taped upside down over the edge of the table so other recipes can be tried while it is being tested.
Distribute worksheets for students to record the recipes they make (good and bad), so that they can keep track of their own changes and compare data with other students to improve on recipes.

Note that this activity does not take into account the drying process of glues - commercial glues need dry time to reach maximum strength.

Discuss how these glues work: the long molecules in some of the ingredients (starch molecules in flour and cornstarch, and protein molecules of casein in milk powder) are able to reach into the tiny cracks in the cardboard and hold onto it, like fingers reaching into cracks in a wall. (The smaller sugar molecules of the icing sugar is not so good at making a glue, unless it is made really thick). This mechanical mechanism is just one of the ways that real glues work.
Distribute worksheets for students to record the glue recipes they create, as well as how long the glue holds the marble to the cardboard. Students can compare data to improve on their glue recipes.

Discuss how these glues work: the long molecules in some of the ingredients (starch molecules in flour and cornstarch, and protein molecules of casein in milk powder) are able to reach into the tiny cracks in the cardboard and hold onto it, like fingers reaching into cracks in a wall. (The smaller sugar molecules of the icing sugar is not so good at making a glue, unless it is made really thick). This mechanical mechanism is just one of the ways that real glues work.

Mechanisms of glues:
The molecules of a glue need to be good at sticking to each other and to the material(s) it is glueing together. There are several molecular processes at work.
Adsorption - the glue and the material have charged molecules that attract each other. It is a weak attraction, but with many of these bonds they can hold the glue and surfaces of the material together.
Mechanical - the long molecules of the glue creep into the tiny holes in the surface of the material(s) and hold them together.
Diffusion theory. The adhesive can diffuse into the surface and vice-versa, with molecules swapping over at the join and mingling together.
Chemisorption - there is a chemical reaction between the glue and the material. (not the mechanism for the glues made in this activity)
From www.explainthatstuff.com/adhesives.html

Grades taught: 
Gr K
Gr 1
Gr 2
Gr 3
Gr 4
Gr 5
Gr 6
Gr 7
Teacher: 
Alane Lublow
Becky Evermon
Cindy Woo
Daphne Gurney
Elizabeth Astbury
Hannah Langille
Ingrid
Jess Christie
Lia Cuccurullo
Nellie Wong
Nina Hooker
Rebecca Kargut
Scott Malin
Taz Ismail
Teaching site: 
ingridscience afterschool
MacCorkindale Elementary
McKechnie Elementary
Selkirk Elementary
Tyee Elementary
Activity originally developed and delivered: 

Tyee
Matter and glue worksheet with McKechnie