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Effect of Salt on the Boiling Temperature of Water

Many people assume that the laws of physics are set in stone. When it comes to the freezing point or boiling point of water, everybody who has ever studied a little bit of science would be able to say water freezes at 32 degrees Fahrenheit and water boils at 212 degrees Fahrenheit. Not many people realize that the boiling point of water can actually be changed, depending on what you place into the water.

This is true for something like salt, which elevates the boiling temperature of water in a process known as boiling point elevation. Basically, water is known as a solvent and salt is known as a non-volatile solute. When you add something like salt to a solvent like water, it makes water become an impure solvent and raises its boiling point above that of pure solvents.

Though salt raises the boiling point of water, it doesn’t do it very much. In most cases, the temperature rise is a matter of only a few degrees F, usually under five. In order to understand this concept, there are many experiments you can conduct, even at home. Here is one of the simplest experiments you can do yourself because you won’t need any advanced equipment or materials.

For this experiment, you will need:

• table salt
• measuring cup
• distilled water
• a cooking pot
• pint measuring cup
• a teaspoon and tablespoon measurement cup
• thermometer
• spoon to stir with

First, boil one quart of the water on a stove. Measure the temperature of the water once it gets to a boil. You should get something around 212 degrees F although it may vary slightly. Then, measure out one tablespoon of salt. Pour it into the boiling water and stir it well. Use the thermometer again to take the temperature of the water and record the finding. It should have risen to around 215 degrees F, although again, it may vary slightly. Now, measure out a second tablespoon of salt and add that to the boiling water. Measure the temperature again and record it, this time reflecting that there are 2 spoonfuls of salt in there. The temperature should be around 218 degrees F, yet another increase.

The increase isn’t all that big and it doesn’t really affect much but it’s an interesting example of how mixing two things together – like salt and water – can change something you wouldn’t even think about at all – like the boiling point of water.

The Effect of Salt: Experiment sheet that explains in detail how the process works and why it does.

The Effect of Salt on the Boiling Temperature of Water: Another experiment that demonstrates how salt affects water’s boiling temperature.

Properties of Salt and Water: Discusses the properties of salt and water and why they change.

Boiling Point Elevation: Outlines the chemical sequence of boiling point elevation.

Experiment: Another summary of a boiling point elevation experiment.

Interactive Experiment: An interactive experiment related to boiling point elevation.

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