Grow your own Crystals An investigative activity by Jenny Douglas, Janet Troy and Vanessa Keenan-Boldt

Introduction

VELS VELS progression points (2.25): Science: Science knowledge and understanding Awareness of similarities and differences between materials in a group Knowledge of everyday changes related to matter… Science at work Recoding of observations made during teacher directed experiments involving measurement in the collection and recording of data Recognition of simple patterns evident in collected data Awareness of safety procedures undertaken during experiments

Purpose To see if we can grow our own crystals – is it possible?

Hypothesis That mixing salt and hot water will result in crystals forming That crystals can be grown in the classroom in a short period of time

Materials A glass jar A measuring cup 1 cup of boiling water ½ cup of salt A pencil Cotton string A spoon A paperclip Paper towel

Method 1 Tie the paperclip to one end of the cotton string, and the pencil to the other end. Place the pencil on the top of the jar so that the paperclip is just touching the bottom of the jar. Remove from jar and set aside for later. Boil the water. Pour the boiling water into the jar Add the salt very slowly, about 1tsp at a time, stirring between additions until completely dissolved. When you find that the salt stops dissolving, you have added enough and your mixture is supersaturated. Lower the paperclip and sting into the water and rest the pencil across the top of the jar. Cover the jar with the paper towel. Place the jar where it won’t be disturbed for a couple of days After about 12hours you should be able to see small crystals forming at the bottom of the jar, on the paperclip and on the string.

Method 2 To produce a variable we decided to try our crystal experiment with a food colouring additive. We followed the same method in our previous example and added food colouring to boiling water, room temperature water and cold water.

12 Hours later Foggy substance forming around top of glass. Salt at bottom of glass taking on pink colouring. Small vein-like sticks protruding from string. Random lumpy bits floating in glass.

48 Hours later Vein-like sticks protruding from string are more prominent. Foggy substance around glass is more pronounced. Dry part of string has formed thick salty substance. Tiny square crystals beginning to form on string that is in water.

More results Left picture contains room temperature water and Right picture contains cold water after 48 hours. Both showed little change except for a crusty salt residue around the dry part of the string. The cold water started and remained quite bubbly.

Discussion

Conclusion

Delegation of Activity