When you add salt to water you are going to boil, I believe it causes the water to boil at a higher temperature, meaning it takes the water longer to boil, but once you add the food to it, the food will cook more quickly in the hotter water. However, everyone else I’ve talked to thinks that the reason you’re told to add salt to water you’re going to boil is because a) the water will boil more quickly, or b) the food will taste better. I’m pretty sure I’m right, but can anyone explain the exact chemical reason why? No one was satisfied with my explanation.
I’ve heard it won’t make the water boil faster unless you put so much salt in that it would actually ruin whatever you were preparing.
The difference in times and temperatures for boiling and cooking are so small for the amounts of water and food and salt you are likely to be using, pay much more attention to the way it makes it taste. Pour the salt into the almost boiling water, and it will suddenly come to a boil. That happens because the energy that was used to keep the salt crystallized is released into the water. It also causes a lot of the water to evaporate, and cool the whole. None of this makes more than a few seconds of difference in the process of cooking.
The presence of salt in the food, or in the water and the relative proportions of those concentrations will affect whether the net osmosis of water, and salt is into the broth, or into the food. More salt for broth, or for foods that need salt, less salt for liquid you will discard, and foods with their own salt.
Over the long run, the best advice is what it says in most recipes; Salt to taste.
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Water with salt disolved in it has a higher boiling point than pure water (it also gives it a lower freezing point, which is why you can melt ice by putting salt on it). I don’t know what the actual temperature differential is, but it isn’t a very big deal, so you shouldn’t worry about it (except to tell your friends that you were right and they were wrong).
A quick search of the net has yielded a formula on this page: http://www.treasure-troves.com/chem/BoilingPointElevation.html .
I’ve forgotten the chemistry for why this is the case, however. My first guess would be that it’s along the lines of “you can’t have salt ‘dissolved’ in water vapor or solid ice (i.e. you need liquid), so you have to work harder to get it out of the liquid phase because of this extra barrier”.
If you’re talking about cooking pasta, the only reason to put salt in the water is for flavor. I never put salt when I’m cooking pasta and it cooks just as fast as it tells you it will on the labor. Whatever effect the salt has on the boiling point is negligible.
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The only reason I put salt in water is to cook pasta, such as RealityChuck mentioned. However I do not do it for taste, I believe it helps in preventing the pasta from sticking/clumping together… my sister would take a different approach and use olive oil.
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Colligative properties is rattling 'round my brain trying to assert it’s self. Someting about the way the water molecules wrap themselves around the dissociated sodium and chloride ions that effects surface tension? Any chem majors want to straighten me out?
Larry
Close…
Colligative properties refer to freezing point depression, boiling point elevation, and osmotic pressure. They are grouped together because they depend only on the number, and not the identity, of the solute particles in an ideal solution. The normal boiling point of a liquid occurs at the temperature where the vapor pressure is equal to 1 atmosphere. When a nonvolatile solute is dissolved into a solvent it decreases the number of solvent molecules per unit volume. Thus it lowers the number of solvent molecules at the surface, and proportionately lowers the escaping tendency of the solvent molecules. Therefore a nonvalatile solute lowers the vapor pressure of a solvent. This means that the solution must be heated to a higher temperature than the normal boiling point to reach a vapor pressure of 1 atmosphere. In the case of table salt, the boiling point elevation is not as great as calculated. This is due to ion pairing. Because the Na and Cl ions sometimes pair up in the water, they behave as one particle instead of two separate particles. This lowers the expected boiling point elevation somewhat.
IMTERESTIMG.
“Pour … salt into … almost boiling water, and [the
water] will suddenly come to a boil. That happens
because the energy that was used to keep the salt
crystallized is released into the water…”
Seems a bit far fetched to me. The salt acts as a temporary ‘boiling stone effect’ which we already talked about.
We seldom think of salt as holding and releasing energy—even though we talk alot about smaller powerful things (like atoms) doing it.