Why should water be most dense at 4°C?
609672
Most liquids dilate when heated and therfore the density increases with temperature. Water is an exception below 4 degrees Celsius. The reason are hydrogen bonds. \n\nIn the H20 molecule the hydrogen atoms share their electrons with the oxygen atom in socalled covalent bonds. But the oxygen atom attracts the electrons very strongly and takes more than its share.\n\nAs a consequence the hydrogen atoms form bonds with the oxygen atoms of other water molecules. These hydrogen bonds are weaker than the covalent bonds. \n\nThe result of the existence of hydrogen bonds is that ice is organised in a hexagonal structure which is less dense than water. These structures form already in liquid water too, but to a lesser degree.  \n\nThe end result is a tug-of-war between the effect of the hydrogen bonds and the normal dilation of water. With a maximum density at 4 degree C as a consequence.
608826
It's in reference to density and is the ratio to the density of water at 25 degrees celcius.\n\nBasically, water is 1 g/cm^3. So something with a specific gravity of 25 will have a density of 25 g/cm^3.
402591
The short answer is an ice cube, but that is not the whole story.  Water reaches its maximum density at about 4 degrees centigrade at which point it is still liquid.  The density drops at temperatures below 4 degrees, ice forms at 0 degrees and the density continues to drop as things get cooler.  The density also drops as water is heated.\n\nSo at 60 degrees centigrade, liquid water has a density of about 983kg/m3 while at -10 degrees, ice has a density of 998kg/m3.  This means the ice more dense than the water, so if you drop an ice cube at -10 into a cup of water at 60, the ice cube will sink (if you can stop it from melting or cooling the water).\n\nAssuming your teacher asked you this, you can put their nose out of joint by telling them ice is more dense than water and when they contradict you ask them to calculate the density at the temperatures I gave and tell them to ask more precise questions next time.
323097
Ice has a lower density than water. When water freezes, the way in which the molecules rearrange to make a solid means that they are slightly further apart than in liquid water. Since density = mass/volume, and in ice there is slightly less mass in the same volume, ice is less dense.\n\nTherefore, because of Archimedes' buoyancy principle (the upward force on an object in liquid is equal to the mass of substance *displaced* by the object), ice floats. The ice displaces a volume of water equal to the volume of ice, but that volume of water has more mass than the same volume of ice, so the upward force is greater than the mass of ice. So the ice floats.
71290
Solid (frozen) water is lighter than liquid water.  Since low density materials float on higher density materials, ice floats on water.  \n\nSolids are typically poor condutors of heat, so ice forms an insulating barrier between the cold air and the warmer water below.  This insulating effect is what keeps lakes from freezing solid.\n\nIf ice was denser than water, ice would sink and liquid water would rise up to contact the freezing air above.  Even the deepest of lakes and rivers would freeze solid.  Life as we know it could not exist over most parts of the earth.\n\nIt is important to remember that most solids are denser than their melted (liquid) forms.  Water is very unique.  Since we cannot imagine life without floating ice, scientists are looking for water in the cosmos as signs of places that we, or other beings might be able to inhabit.
916456
The density of water goes down when it is frozen and down when it is heated, so I would say just above freezing.  According to the website, about 4 degrees C.  The density of water at this temperature is 1.000g/cm3
885641
Assuming that they have equal masses, it would be whichever material has the highest specific heat, because that defines how much heat energy is required to increase a unit mass of material by a unit temperature.  Water is known for having a very high specific heat, so it could be that, but you should really look up the specific heat (or "specific heat capacity") for all of these materials in your text book.
379878
Density is the key property that determines whether or not a substance floats.  Ice floats because it is less dense than liquid water.  Why is ice less dense?  Because the water molecules in ice are arranged in a crystal lattice that spaces the molecules farther apart than when they are in the liquid state.  That is why ice floats.  \n\nBy the way, your initial statement that cold water is heavier than warm water is not exactly worded correctly.  It is more correct to say that cold water is denser than warm water, not heavier.
649898
No, that is not true.  If you have a more dense metal, it may take more energy to heat it up, but that is because there is more mass.  Water has a very high specific heat, but it is definately less dense than metals.  I believe specific heat is determined by quantum mechanical properties.
685263
as you know the density of ice and water is slightly different.\n\nmultiply the height by the ratio of densities, i.e. density of water/density of snow.\n\nIce has a density of 0.917 g/cm³ at 0 °C, whereas water has a density of 0.9998 g/cm³ at the same temperature
405810
Water has a special property, called Anamolous behaviour of water, and this property is seen only in water.\nWater's melting point is 0 degree Celsius, and you might think that the volume increases if further heated above 0 degree celsius, and you are wrong ! Only in water, the volume of water decreases until it is heated to 4 degree celsius, and then it starts increasing, unlike any other liquid (in other liquids, replace 0 degree by their melting point). Therefore, volume of water is least at 4 degree celsius and not at 0 degree celsius. This property of water is called Anamolous Property of water or Anamolous Expansion of water.\n\n--\nWWW - Weird & Wonderful Web - http://www.kudige.blogspot.com/
243894
Hydrogen bonding causes water to expand upon freezing.  The H-bonds cause the molecules to align into a structure that occupies more space than the liquid.  \n\nLiquid H2O does not do this because the kinetic energy of the water molecules constantly breaks any H-bonds that form.  As the kinetic energy (temperature) of the water decreases, the water becomes more dense, down to about 4 deg. C.  \n\nBelow 4 deg. C, the H-bond alignment of molecules outweighs the kinetic energy and the density of water begins decreasing.\n\nFrom Wikipedia:\nA simple but environmentally important and unique property of water is that its common solid form, ice, floats on the liquid. This solid phase is less dense than liquid water, due to the geometry of the strong hydrogen bonds which are formed only at lower temperatures. For almost all other substances and for all other 11 uncommon phases of water ice except ice-XI, the solid form is more dense than the liquid form. Fresh water is most dense at 4°C, and will sink by convection as it cools to that temperature, and if it becomes colder it will rise instead. This reversal will cause deep water to remain warmer than shallower freezing water, so that ice in a body of water will form first at the surface and progress downward, while the majority of the water underneath will hold a constant 4°C. This effectively insulates a lake floor from the cold.
786403
a) a lower freezing point than pure water
838267
Density plays an important role in the working of the planet.  Less dense things rise above more dense things.  Also, density changes with state (solid, liquid, gas).  Consider water, it is the only substance where the solid form is less dense than the liquid form.  Because of this, ice floats.  Imagine if ice didn't float, but sank.  When the tops of lakes froze in the winter, the ice would sink down to even colder areas (and not melt), then the next layer would fall on top of that one.  Eventually the whole lake would be a block of ice.  There might even be similar events with entire oceans or at least in the polar regions.   Density also affects heat transfer.  The more dense something is, the more molecules there are in contact with each other.  What heats up faster, air or cement?  Cement, because the molecules constantly collide with each other whereas in air, there is so much empty space that they often miss each other.  Therefore there are fewer collisions and less heat is transferred.  Hope this helps get your mind jogging.
584455
When the whole ice will melt, water will not come out of the cup, the reason being this. the density of water is maximum at 4 oC and ice which is at 0 oC is less dense than that of water. so, according to the relation: density= mass/volume or inversly you can say volume=mass/density, the volume occupied by ice is more (being less dense, inversely proportional to density), and that occupied by water (which will be formed after ice will melt) is less (being more dense than ice). so water formed from ice will be occupying less space than ice and the water will not come out.
312206
Water continues to become more dense as it cools until just above the freezing point.  I can't remember the exact temperature off-hand, but I believe it is very near 33.5 to 34 degrees Fahrenheit.  \n\nBelow that water begins to expand and once it has frozen, its volume increases approximately 10%...that's why ice floats...less dense than the water it came from!  Cool, huh?
192094
um. well i would assume itz cuz some of it has a lower density than water and some has a higher density? lower density meanz more holes and stuff in it and higher density means   packed more tightly? hahah. why do you care?