Physics Van 3-site Navigational Menu

Physics Van Navigational Menu

Q & A: Analyzing salt water

Learn more physics!

Most recent answer: 06/29/2018
Q:
How can you tell the difference between a glass of pure water and a glass of salt water without having to taste the water?
- Anonymous (age 13)
piqua, ohio, united states
A:

  Four quick ideas,

1)  Measure the density.  If the glasses are identical (have the same mass) and the volume of water is equal, just put the two glasses of water on a balance and see which one weighs more -- thatís the saltwater one.

2)  Put a drop of the water from one on the end of a nail or something and put it in a gas flame.  The salty one should turn the flame yellow/orange.  Try this with the nail with nothing on it first to see if it causes a false positive.  Even a tiny amount of salt (for example, from a little leftover sweat from your fingers) will turn the flame yellow/orange.

3)  Measure the electrical conductivity -- an ohmmeter with probes you can stick in the glasses should do just fine.  Saltwater conducts electricity much more than the pure water.

4)  Let them evaporate -- the saltwater glass will leave a caky residue absent from the pure water glass.  You may not even have to evaporate very much of them before you see the difference on the sides of the glasses.

Can you think of more ways?

 Tom

(published on 10/22/2007)

Follow-Up #1: salt deposits

Q:
BOILING SALT WATER DOWN TO NOTHING IN A PAN WILL LEAVE A WHITE DEPOSIT - RUGHT?
- BARBARA A VOROBEL
53017
A:

Sure, that's just the salt.

Mike W.


(published on 06/29/2018)

Follow-up on this answer.