Most full scuba tanks have a pressure of between 1,800 p. s.i. and 3,000 p. s.i. (pounds per square inch). approximately 70 to 85 cubic feet of air has been squeezed into the tank. when a diver takes his air tank to be refilled, the dive shop will hook his tank to a compressor with a pressure hose and place his tank in a tub of water while it is being filled. what reasons can you give for placing the tank in water?

I would think that because water has a high specific heat, the water in the tank must be cold. Because the scuba tank is at high pressure, and the water is cold, the gas put into the tank will be more compact, and will not expand. According to Charles' law, as temperature increases, volume increases and because in this situation temperature is decreasing, volume will decrease. It would be great to keep the tank into the water because under these conditions, you can store more oxygen into the tank per square inch.

I hope this helps:)

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The answer to your question really depends on three things: how much water you have, how cold it is to start out, and how cold the things around it are. water actually freezes when it gets to 32 degrees fahrenheit (0 degrees celsius), but the time it takes to get there may be different.  let's start with the first. if you take two glasses, and fill one with a tiny bit of water, and the other about halfway, then put them both in the freezer, the one with less water will freeze first (you can try this at home, but i recommend using plastic cups and not glass ones).  now let's move on to the second part. let's say you have two glasses, and you fill one with really cold water that has been in the refrigerator, and the other with really hot water from the sink. if you put both of them in the freezer, the one that started out colder will freeze first.  for the third part, let's imagine that you have two glasses with the same amount of water in them, and the water is at the same temperature. imagine putting one outside on a really really cold day in georgia, and having a friend in alaska put one outside on the same day. since it would be so much colder in alaska, the glass of water there would freeze before yours.  so, if you took a tiny bit of really cold water in a glass, and put it outside on a cold day in alaska, it would freeze a lot faster than a big glass of hot water outside on a cold day in georgia.