SMMART SCIENCE: MAGIC ICE
Has your child noticed that sometimes there is salt sprinkled on the ground to melt the ice in the wintertime? Well, salt plays a magical role in this great learning activity.
First, to establish a little background with your child, you might wish to set out two plates of crushed ice. Let your child sprinkle salt on one plate of ice and observe together which plate of ice melts first. Now your child will see that salt helps ice to melt.
This is because the sodium and chloride ions from the salt intermingle and dilute the water molecules. This makes it harder for the water molecules to join together to form ice crystals. Actually, it's still possible for the water molecules to form ice crystals, but now instead of freezing at 0°, it's freezing point drops to below 0°C.
Now, for the activity, Fill a small glass with water and ice cubes. Give your child a piece of cotton string or yarn about a foot long. Let your child hold both sides of the string and rest the remaining middle part of the string on top of the icecubes. Take care to leave the ends of the string hanging over the edge of the glass.
Have your child count to 15. Now instruct her to take both ends of the string and pick it up, while lifting up a piece of ice with the string. The string is not attached to the ice and will not lift the ice.
Now, have your child lay the string back onto the ice with the ends of the string laying over the sides of the glass. Have your child sprinkle salt all along the string laying on the ice. Now count to 15 slowly.
Ask your child to pick up the ends of the string and try to pick up the pieces of ice now.
The salt caused the ice under the string to melt slightly. Then the cold water aids that thin bit of melted ice to refreeze. Since the string has soaked up water, it freezes to the ice cubes. Ice crystals reform, trapping the string. Now your child can pick up the ice cubes along the string like a necklace.