Dry ice sinks in water because the density of dry ice, which is 1.2 grams-per-centimeter cubed, is greater than the density of water, which is 1 gram-per-centimeter cubed. Calculate the density of a material with information from a math and science teacher in this free video science lesson.
Hi, I'm Steve Jones, and I'm going to tell you why dry ice sinks. Now, let's get the question correct here. Why dry ice sinks in water? Of course, if I try to float dry ice on mercury, it will float, iron will float on mercury. This is a different question. Why dry ice sinks in water? Sinking and floating has to do with density. That is, how much a cubic centimeter, or cubic meter of a material weighs? A dense material weighs a lot, for the same amount of material, the same volume of materials, same space taken up, so the trick is simple. If you look at the density, you'll find, if you have a block of ice, solid water ice, and that block is a centimeter cubed, it will have a weight of 0.9 grams or so. If I take the same amount of water, it actually has a mass of 1 gram, it has a bigger mass. Now, that means that the less dense material, is ice. If I however, look at dry ice, which is solid carbon dioxide, dry ice for that same little cube, one centimeter by one centimeter, by one centimeter, it will be 1.2 grams per centimeter cubed. That is, that same block, weighs 1.2 grams. Now, 1.2 grams is greater than the 1 gram, that the water would weigh, and therefore, it would sink. It pushes down against the water. The water can push upwards, up to an amount of 1 grams worth, and then it has to give up, because the dry ice can continue to push, so that is basically why, dry ice sinks.