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Q & A: Ice cubes: Tap water and distilled water

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Q:
What is the difference between ice cubes made of tap water and ice cubes made of distilled water?
- Tarsha (age 13)
Old Court Middle School, Baltimore, MD USA
A:
The only difference between ice cubes made of tap water and ice cubes made of distilled water is that ice cubes of tap water contain impurities in the water that distilled water does not have. Distilled water contains H2O molecules and very little else. Tap water is not as highly purified, so it may contain (small amounts of) a number of different substances such as salts (especially calcium salts), nitrates, chloramines, fluorides, and sometimes some very tiny microorganisms. The actual composition of your tap water depends where the water is drawn from and on how the water treatment plant filters it. Tap water varies from location to location, and it may even be treated within the home to change its properties. For example, water "softeners" replace calcium salts with sodium chloride (the same as table salt) to improve the way soap works with the water. The levels of impurities in tap water are tightly controlled by government regulations and are usually quite low.

When the water freezes, most of these impurities are not actually included in the ice crystals, but they usually do get stuck somewhere in little pockets in the ice cubes. Thatís why, with our very sensitive sense of taste, we can tell the diference between different types of ice cubes, the same as you can taste the diference between water from different sources. These small differences between tap water and distilled water may not produce any obvious visible difference in ice cubes, however.

A less subtle difference might arise from the fact that many taps "aerate" the water by passing it through a fine mesh with an air intake. Tap water out of most taps has quite a bit of air dissolved in it. If you leave a glass of tap water out for a while you may notice tiny air bubbles forming on the side. If you freeze the water quickly, the ice will form before the air has a chance to bubble out. The bubbles will form anyway inside of the ice cubes because the dissolved air does not fit into the ice crystal lattice. So if you look at ice cubes made from tap water compared with distilled water, you might find that the tap water ones are not as clear and transparent as the distilled water ones because of all the air bubbles inside. But this isnít a fixed property of tap water or distilled water, just in their handling (you can dissolve air in the distilled water too!).

(republished on 07/25/06)

Follow-Up #1: electrolytes

Q:
1. Why is tap water more conductive than distilled water 2. What is ionization 3. What is an electrolyte 4. Differentiate strong elctrolyte from weak electrolyte from the point of view of ionization 5. What is non-electrolyte 6. describe the intensity of brigthness between the Acids and Bases 7. In general what do your say about the conductivity of most salt solution
- Miracle Sarmiento (age 17)
Manila Philippines
A:
1. The salts in tap water fall apart into electrically charged particles (ions) in water. In an electric field, these ions are dragged one way or the other, depending on their charge, giving an electric current. That's called electrical conduction.
2. Ionization means that some atom or molecule loses or gains one or more electrons, so that the negative charge of its electrons doesn't just balance the positive charge of its nuclei.
3. An electrolyte is anything that ionizes in water.
4. beats me. Maybe strong electrolytes are more soluble in water.
5. Something that doesn't ionize in water.
6. What does that mean? Is this part of some school assignment?

Mike W.

Lee H


(published on 03/03/07)

Follow-Up #2: Where does water come from?

Q:
Where does water come from
- Alyssa Mahan (age 11)
New Yourk
A:
Water,  H2O,  consists of the two elements, Hydrogen and Oxygen.  There is plenty of both around in the solar system and on earth.   Hydrogen and Oxygen attract each other and love to get together to form water molecules. 

Water has several different forms other than a liquid. If you cool water down below 0o Centigrade (32o Fahrenheit), it freezes to make ice.   It you heat water to 100o C (212o Fahrenheit)  it will turn into a gas. 

LeeH

(published on 02/08/10)

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