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Name:   Frank V.
Status:  other
Age:  8
Location: N/A
Country: N/A
Date: 2000


Question:
My 8 year old son has done a science fair project entitled "Does an Ice Cube Melt Faster in Fresh Water or Salt Water?".We have done the experiment several times and have concluded that an ice cube melts faster in fresh water. Can you help me explain the experiments results,so an 8 year old can better understand it.


Replies:
Hi Franck! So you have the correct answer, you did some experiments and found correctly that an ice cube melts faster in fresh water...

Why?

Every pure substance has a definite temperature where it melts. It is called melting point. (it is similar to the boiling point where a pure substance boils). We can say that the temperatures in both cases are related to the forces that hold the molecules together. There is a physical constant called "molar heat of fusion" that somehow controls the melting point temperature. When you have salty water, the salts in the water make the molar heat of fusion, (and the melting point) lower, and this means that the ice inside this salted water will melt only at a lower temperature. And the ice cubes will melt slowly...

That is the same principle one use when put some salt over an ice pack to freeze some beer cans...The ice will stay longer...

I hope, Dad, that the explanation will be satisfatory for your 8 year old son.

And tell others about NEWTON! It is a pleasure to answer your questions!

Mabel
(Dr. Mabel Rodrigues)



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