how can this be? Calling science experts?

Question

at temp 0 degrees Celcius, density of water is .998 (g/ml) then goes up to.999 at 2 degrees, to 1.0 at 4 degrees, then down to .999 at 6 degress and finally to .997 at 10 degrees celcius. Why would it have dropped in density after the 4 degrees? Wouldn't it stay the same density as it is ice?

Answer 1

water does some strange and interesting things as it freezes.

most substances become more dense as they freeze. water acts as a typical liquid up until 4 degrees C. it is at this point, when water begins to arrange its molecules in a crystal-like structure. this structure is more spread out than that of water, giving ice a lower density than water. (the crystal-like structure is kept in place because oh the hydrogen bonds between the molecules. at lower temperatures, the molecules don't have enough kinetic energy to break out of this structure, but as water melts the crystal structure is broken making water once again more dense than ice.)

good question!

Answer 2

Water is a weird liquid. Starting from 10 deg C and going to 4 deg C, the increase in density is expected. The maximum at 4 deg and subsequent decrease in density to 0 deg is not.
This has to do with the polarity of a water molecule, which is negative at the O end and positive at the end with 2 H. Think of a triangular molecule. Overall, the charges even out, and at high temperature, the motion of the molecules overcomes the attraction between adjacent molecules that could set up. At 4 deg C, the motion just equals the attractive forces. Below 4 degrees, apparently, some "ice islands" start to form in the liquid water where the attractive forces can locally set up an ice structure. The ice structure is wider than the mean differences in liquid water, so ice is only about 90% the density of water. As the temperature heads for 0 deg C, there is an increase in these "ice islands". However, even at 0 deg C in water, only a small amount of liquid water is converted to "ice islands".

Answer 3

generally as you heat a substance the density decreases due to the volume increasing ( more energy so that the molecules push further apart) and visa versa, as you cool a substance the density increases because the volume decreases (the molecules have less energy so that they come closer together).

Water however does not follow this. Water is a polar molecule and one of the properties of this molecule is that loose bonds form between the H atoms on one molecule and the O atoms on another molecule. This forms a pseudo larger structure and is commonly termed hydrogen bonding.

Due to hydrogen bonding water has a maximum density of 1 at 4°C. The energy imparted at higher temperatures causes the volume to increase (molecules push further apart) and the hydrogen bonding causes the volume to increase at lower temperature (the force of the hydrogen bonding pushes the molecules apart, overcoming the attraction of the molecules due to their lower energy).

If this wasn't the case the oceans would be very different as the ice on top of the water would sink. Actually we probably wouldn't be here

Answer 4

At 4 deg C, water is at max density. As water cools further to 0 deg C (freezing) its density decreases, so it is actually less dense in the solid form (ice) than it is in the liquid form (liquid water). This is why ice floats, and fish can live in lakes which freeze over in the winter - a layer of ice forms on top of the body of water, always leaving some liquid water in which the organisms can continue to live.

Answer 5

Water is at its denestest at 4 degrees C. It sinks and causes turnovers in very deep lakes. The "L" shaped molecules get the closest together at 4 degreesC. Then they start lining up to form ice crystals which we know are less dense than water, they float. In ice they have to line up the "L" shapes and there is space between them.

Answer 6

Not necessarily. Ice can expand and contract to a point at different temperatures. It is more stable but it is not locked in to its specific density.