What can boiling water chemically change?

Does salted water boil faster?

Depending on what is meant by "faster". If the question is: "Does the boiling point decrease when you add salt to the water?", Then the answer is very clear: "No!" On the contrary, it increases!


Boiling means: The water molecules move so fast that they separate from each other, so that the liquid water becomes water vapor. However, salt in the water causes the water molecules to bind to the salt molecules. As a result, the water molecules have to move even faster in order to tear themselves away from the salt and change into the vapor phase. The fact that they move faster means nothing more than that the temperature rises. And the higher the more salt I add. However, there is an upper limit. This is achieved when the water is saturated with salt. If the salt content is slightly more than a third, the water cannot dissolve any additional salt. And with such a saturated salt solution, the boiling point is 108 degrees Celsius. When cooking spaghetti in the kitchen, we don't add quite as much salt as the boiling point increases by 1-2 degrees, i.e. around 102 degrees.

But you said earlier that there is another answer to the question.

So far I've only talked about the boiling point, which increases when you add salt. But strictly speaking, the question was: does the water boil faster? Now one might suspect that the water on the hob takes longer to come to a boil when the boiling point is higher. But this is not necessarily the case, because when you salt water, you also increase the heat storage capacity up to a certain point. That means in plain language: The water gets hot faster with a certain energy input because it converts the supplied heat energy into temperature degrees more quickly. So it takes less time to go from 20 to 100 degrees on the same hotplate. Now, if it's salted, it doesn't boil until it reaches 102 degrees, but the bottom line is that even that is still a little faster than if you bring the unsalted water to a boil. All of this can be calculated physically, but in fact you will hardly notice any difference in the kitchen. Salting is basically not good for saving energy.

If you have bubbly boiling water in the pot and then pour salt into it, it puffs up briefly, but the bubbling subsides. How is that explained?

Because adding salt increases the boiling point. Suppose I have boiling water at 100 degrees Celsius in front of me and add salt. Then I raise the boiling point in one fell swoop. Suppose the water was still a hundred degrees, but then suddenly it would be two degrees on the way to the boiling point; so it stops boiling. This effect is reinforced because the water even cools down slightly due to the addition of salt. Firstly, because the salt usually only has room temperature, so it would first have to be heated. Above all, however, because dissolving salt in water costs additional energy - in other words: When the salt dissolves, the water cools down.