Why Does Filtered Water Melt Faster?
Most recent answer: 2/5/2011
Q:
Thank you for answering my question! We tested the water with an aquarium test kit and the distilled water had a low pH. The filtered water and the tap water had a high pH.
My mom wants to know if some of the carbon from our water filter might get in the filtered water and if that's why the filtered water melted faster than the tap water?
- Audrey (age 8)
Kingwood, Texas, U.S.A.
- Audrey (age 8)
Kingwood, Texas, U.S.A.
A:
Interesting question. Since the distilled water was the one with low pH (acidic) it's the one most likely to have a lot of dissolved CO2. Since it's distilled, other acids should be pretty well removed. (I'm assuming that low pH here means less than 7.0.) There's no special reason to think then that the carbon from the water filter came off into the water, at least in such a simple form. So I'm a little more puzzled about why the filtered water melted noticeably faster than plain tap water, now that it sounds like they have about the same pH.
Have you tried letting each of the types of water sit for a long time at room temperature before freezing them? Maybe some other dissolved gases are involved, and if they sit long enough those will reach equilibrium. Just scrambling here.
Mike W.
Have you tried letting each of the types of water sit for a long time at room temperature before freezing them? Maybe some other dissolved gases are involved, and if they sit long enough those will reach equilibrium. Just scrambling here.
Mike W.
(published on 01/30/2011)
Follow-Up #1: Melting tap water and distilled water
Q:
I'm trying to get a clear definition as to why the following happened. My daughters experiment was to see if purified ice melts faster than city water ice. The experiment used DI water at 0 ppm and city water at 279 ppm. The ice was allowed to melt into itself in plastic cups. the city water melted slower than the DI water.
We did not melt it in a salt solution etc just let it stand alone. I thought the city water ice would melt quicker because of the lower melting/freezing point but I guess this is not the same in this example.
- geoff Hepworth (age 44)
Los Angeles, Ca, USA
- geoff Hepworth (age 44)
Los Angeles, Ca, USA
A:
I've marked your question as a follow-up, because it's closely related to others.
You don't say what the ppm's are of. Salt? At any rate, you're right that any solute lowers the melting point, so it's a little surprising that the distilled water melts first. Maybe what's going on is that the salt dissolves in the first water that melts. This make a dense layer. The ice then floats on that layer. As more water melts, it take a while for it to mix with the salty water. So the ice is left sitting in the just-melted coldest water on top. That slows the melting, compared with ice sitting in better-mixed water. I'm a little surprised that this effect is important for such low salt concentrations, so perhaps something else is going on.
Mike W.
You don't say what the ppm's are of. Salt? At any rate, you're right that any solute lowers the melting point, so it's a little surprising that the distilled water melts first. Maybe what's going on is that the salt dissolves in the first water that melts. This make a dense layer. The ice then floats on that layer. As more water melts, it take a while for it to mix with the salty water. So the ice is left sitting in the just-melted coldest water on top. That slows the melting, compared with ice sitting in better-mixed water. I'm a little surprised that this effect is important for such low salt concentrations, so perhaps something else is going on.
Mike W.
(published on 02/05/2011)