1. Grade 9/10 Alex Foo – Alexfoo138@gmail.com
Chemistry Demos
Grade 9/10
Alex Foo –

2. Overview Introduction to chemical changes Colour change reactions
Blue bottle
Cobalt chloride equilibrium
Glow in the dark
Slime/polymers

3. Blue Bottle - Protocols
Methylene blue
NaOH
Glucose
Dissolve 1.5g NaOH, 1.7g glucose in 250mL water
Add 5-7 drops of 5% methylene blue solution
Wait until blue colour disappears
Shake flask vigorously to produce colour change
Methylene blue is commonly used as a biological stain
- Also available from pet stores – antiparasitic drug for fish

4. Cobalt Chloride - Protocols
Cobalt chloride (CoCl4 · 6H2O)
Concentrated HCl
Ice/hot water
Test tube
Dissolve 4g of CoCl4 · 6H2O in 40 mL water to form a red solution
Add HCl until solution becomes slightly purple
Add more water if you overshoot
Add the CoCl4 solution to a test tube.
Immerse the test tube in hot water to produce a bright blue colour. Immerse in cold water to reverse the reaction

5. Teaching Notes
Blue bottle: Oxidation of methylene blue by atmospheric O2 produces blue colour
Glucose reduces methylene blue back to colourless form
Cobalt chloride: chemical equilibrium between two coloured species altered by change in temperature
Very visual examples of colour changes as a result of chemical reactions
Higher grades – le chataliers principle
Leading questions – observe what happened. Is this a chemical change or a physical change? How do you know?
Highlight the fact that chemical changes are reversible
Highlight the fact that sometimes it is not easy to differentiate chemical changes from physical changes based on macroscopic observations. However, IF we know the chemistry behind a given compound, we can predict whether a given change it undergoes is a physical or chemical change
Red
Blue

6. Glow in the dark - Protocols
Luminol (ebay)
Fluorescein (optional – highlighter juice)
Bleach
Sodium hydroxide
Water

7. Glow in the dark - Protocols
Luminol (ebay)
Fluorescein (optional – highlighter juice)
Bleach
Sodium hydroxide
Solution A: g luminol and 0.4g NaOH in 100 mL water.
Add a pinch of fluorescein if desired
Solution B: 1% bleach
Chill, mix and watch!
Note: reaction works best when both solutions are cold

8. Glow in the dark – Teaching notes
Luminol is oxidized by the bleach to form a diacid
Product initially contains an electron in the excited state
Electron quickly relaxed, releasing light
Example of the production of light in a chemical reaction
Release of chemical energy

9. Slimes and Polymers - Ingredients
Polyvinyl alcohol
Borax
Water
Slime 2:
Sodium alginate
Calcium lactate or any other calcium salt
ebay
- Amazon.ca
Fine food stores
Spherification

10. Slimes and Polymers - Protocol
Prepare 6% PVA solution in water
Need to boil water to ensure complete dissolution
Prepare saturated borax (4%) solution
Combine 30 mL of PVA solution with 8 mL of borax. Add food colouring to taste
Mix well to form a slime

11. Slimes and Polymers - Protocol
Prepare a 0.75g/100mL solution of sodium alginate in distilled water
Add food colouring to taste
Prepare a 2g/100mL solution of calcium lactate in distilled water
Pour 200mL of calcium solution into a clear beaker
Add the sodium alginate solution slowly
The alginate solution will polymerize instantly upon contact with the calcium solution, producing long “snakes”

12. Teaching notes:
Polymerization involves the formation of chemical cross-links between individual molecules
Resulting solid can signify a physical change
Are all reactions which produce a solid the result of a chemical change?

13. Hard Water - Protocol Calcium acetate (ebay) Isopropanol
Prepare saturated (~35g/50mL) solution in water
Isopropanol
Pour calcium acetate solution into a cup
Add equal amounts of isopropanol
Calcium acetate should precipitate out to form a gel

14. Hard Water – Teaching notes
Calcium acetate highly soluble in water
Insoluble in isopropanol
Precipitates out to form flammable gel
Segue into solubility, physical vs chemical properties
Is this a chemical change or a physical change?
Again, chance to discuss the difference between chemical change and physical change, show that sometimes it can be hard to tell
However, if we understand the chemistry behind it, we can make an educated guess, and propose a hypothesis or mechanism through which this change occurs.