Science Sunday - White Spots in the Ice

After our fun with ice and salt the other day, we headed back into the house to research the answer to the question, "What makes the white spots in the ice?"

The most popular hypothesis on the Internet seems to be, that the white spots in ice are a concentration of air bubbles, or minerals, and other impurities in the water, corralled together into one spot in the ice, as the water freezes from the outside in, and top down, because water in its liquid state, can hold more air, and minerals, than in its solid state.

We observed a glass of tap water, and could see both air bubbles, and little floaty bits, so the hypothesis seemed valid.

We decided to put it to the test, and freeze a Dixie cup full of tap water...


...and one with filtered water from our fridge, which we reasoned, should have fewer impurities.


We also prepared a cup with boiled, filtered water, thinking it might reduce the amount of air in the water. And, then remembering the tea-lore, that says microwaved water has less oxygen in it, we microwaved a cup's worth, too.


We put them into the freezer, and left them until this afternoon, when we pulled them out to discover...


...well, they were all pretty much the same. Filtering, boiling, or microwaving the water did not change the size of the white spots in the ice cubes.

We did notice though, that the white spots really do seem to have to do with air bubbles. We could see bubbles rising off the spots, within the frozen water.


So, we didn't disprove the hypothesis, that the white spots in ice are caused by oxygen in the water corralled into place as the water freezes around it. But, it does seem that the white spots have more to do with air bubbles, than with minerals in the water. We need to test further though, maybe with distilled water, to really see.

And, boiling - even in the microwave does not seem to reduce the level of oxygen dissolved in the water. We'll probably stick with the kettle, over the microwave for tea, but we now have some doubt as to the validity of lore. The Tea Muse Newsletter, makes a pretty good case for the kettle though, and even explains some of the science of boiling water - you might want to check it out.

Or, if you're just looking for more science themed fun for children, check out this week's Science Sunday link-up, hosted by Adventures in Mommydom.

It's great to be a homeschooler.