Ice Cube Lifter

Age

Elementary School, Middle School, High School

Format

Hands-on

Materials

   Water
   Beaker
   Ice cube
   String
   Salt shaker 

Safety Precautions

Do not break the glassware. Demonstrators should wear goggles and lab coats, and the ST general safety box should be available to them. Science Theatre demonstrators must keep the safety of themselves and their audience in mind at all times. All Science Theatre demonstrators must have read through the Safety Training page. The ST Safety Box with first aid kit, fire extinguisher, etc. should always be available to demonstrators. Always wear safety gloves, glasses, and a labcoat if handling chemicals; always perform potentially dangerous demonstrations at a safe distance from the audience; and always keep a very close eye on any volunteers you call from the audience.

Preparation

Fill beaker with water beforehand

Demonstration

1) Place ice cube into beaker with water in it

2) Lay middle of the string over ice cube

3) Shake salt over the string

4) Wait a few minutes

5) Lift both ends of the string slowly out of the water, and the ice cube should come with it

What to Say

This demo involves the principles of melting points, boiling points, and dilution. Do you think you can can lift this ice cube out of the beaker with the string, without tying it? Let's see if it's possible. First, I'm going to put an ice cube in this beaker full of water. I'm going to put this string over the ice cube. Now I'm going to put some salt over the string. Let's wait a few minutes... Okay, it should be ready. I'm going to gently pull on the string... The ice cube came along with it! Why do you think this happened?Well, the salt lowered the melting point of the ice cube. So what does that mean? The salt melted the top of the ice cube. When the salt in the water on top of the ice cube spreads out and gets more dilute, the melting point increases and becomes closer to the melting point of pure water. When this happens, the water refreezes from the cold temperature of the ice cube. But this time, it freezes the string to the ice cube. That's how you can lift it!

Why It Is

Salt lowers the melting point of the ice, so the ice melts where the string has landed. The melted ice will eventually refreeze because of the salt water becoming more dilute and from the cold temperature surrounding it. This will also freeze the string to the ice cube. This allows the ice cube to be lifted out of the beaker by the string.

Real Life Examples

Salting icy roads in the winter