What you need:
Ice cubes, String. Salt, A plate, Scissors, Water
What to do:
1. Cut a piece of string about 20 centimetres long.
2. Put a couple of ice cubes on the plate.
3. Now moisten the string with water.
4. Lay the string over the ice cubes.
5. Try to lift the string up. Does the ice come with it?
6. Now, sprinkle some salt over the length of the string that’s in contact with the ice. Leave for a minute.
7. Now, try lifting the string up.
What happens?
Without the salt, the string cannot lift up the ice. But once salt comes into the picture, the ice gets pulled up!
Why?
Water usually freezes at 0 degrees Celsius but it also melts at the same temperature. So the freezing point and melting point of water is the same!
This means, that at zero degrees Celsius, some part of your ice cube is turning into water and some part of that water is turning into ice. But there is a sort of equilibrium so ice and water are in equal amounts. If the temperature falls below zero, more water turns into ice. If the temperature rises, more ice melts into water. Enter salt. Salt dissolves in water. So the water that’s melting takes the salt in and makes it dissolve.
Once the salt molecules are in the water, they start interfering with the other water molecules that are trying to freeze together into ice. So now, the water that’s in contact with the ice cannot freeze at zero degrees Celsius.
You’ll need colder temperatures (minus five or ten or less depending upon the strength of salt) for the water to refreeze. So, salt lowers the freezing (and melting) point of water. However, in this experiment, only a little salt has been sprinkled around the string.
So, the freezing point of only the ice in contact with the string is lowered, and it melts. Thus, the string ‘sinks into the ice. But the melting water soon comes into contact with the rest of the ice and refreezes, this time, around the string. That’s how you can lift up the cube!
Picture Credit : Google
