Melting Point Depression
- Page ID
- 131409
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Required Training |
Required PPE |
|---|---|
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UC Lab Safety Fundamentals |
Lab coat, safety glasses/goggles, nitrile gloves |
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Equipment |
Chemicals |
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Glass baking dish |
Ice |
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String, 20 cm long |
10 g Sodium Chloride, NaCl |
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200 mL Water |
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250 ml Beaker |
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Procedure:
I. Method 1
- Make a large block of ice a few days ahead of time
- Transfer ice to a glass baking dish right before the demo
- Pour some NaCl onto one area of the ice surface
- The ice will start to melt and form a puddle/hole where the ice was poured
II. Method 2
- Place an ice cube of any size in a beaker of water
- Wet the string and lay across the floating ice cube
- Pour some NaCl on top of the string
- After a few seconds the string will freeze to the ice cube and you can lift the ice cube by holding both ends of the string.
Discussion:
The melting point of pure water is 0ᵒ C. As the salt dissolves into the ice, the melting point is lowered below 0ᵒ C causing it to melt faster. Because the phase change from solid to liquid can only occur at the melting point, the temperature on the ice surface drops below 0ᵒ C. This causes the water in the string to freeze to the ice cube slowing the cube to be lifted.
Hazards:
N/A
SOP
N/A
Disposal (by Storeroom)
The ice, water, and ice can all be flushed down the drain.