Daisy

AIM:
My experiment is testing how solute affects the freezing point of a small amount of liquid. The purpose for this experiment is for knowlege. I am using water was the control and water with different amounts of solute in three other test tubes are the experiment group. Each test tube is filled with 20 mL of water and was placed in a freezer -80 C. The temperature of each test tube is measured after five minutes, ten minutes, then twently minutes. There are four test tubes. One with water, one with a 5% salt solution, one with 10% salt solution, and one with 15% salt solution. My experiment is essentially testing how these different levels of solute affect the freezing of the water.

Background :
]]
 * Supercooling** occurs when a liquid is cooled below its equilibrium freezing temperature. For example, water can sometimes be cooled as much as a few tens of degrees below 0°C without freezing. This phenomenon is important in [|cryobiology]. See also [[http://www.phys.unsw.edu.au/~jw/unfreezable.html|What is 'unfreezable water'?

The effects of solutes
What happens if, instead of having pure liquid water, we put some salt or sugar in the water? In other words, what if our liquid phase is a solution? This makes the liquid state less organised, because the sugar molecules or salt ions are free to move about almost randomly. So the liquid water molecules are more disordered (less regimented) in a solution. The ice and the steam remain unaffected however: sugar and salt hardly dissolve at all in ice, nor do they evaporate near 100°C. How does this affect the trade-off between the molecular energy and the molecular order? The gain in disorder on evaporation is now less, because the liquid water in solution is more disordered. The energy effect is hardly changed, so the energy effect dominates over a slightly larger range: the molecules of water in solution have to have slightly more energy (a slightly higher temperature) in order for the two effects to be in balance. So the boiling temperature is higher for a solution. Conversely, when we look at melting, the disorder effect is greater for a solution: on melting into a solution, water molecules go from the high order of crystalline ice into an even more disordered state than pure liquid. So the disorder effect can dominate even at lower temperatures. So the freezing temperature is lower for a solution.

An aqueous solution has a higher boiling point and a lower freezing point than does pure water.
If the solution is not too concentrated, these two effects are approximately independent of what the dissolved substance is: a sugar molecule has much the same effect as a salt ion. So, provided you remember to count each ion separately, the effect of concentration on boiling point elevation or freezing point depression is much the same for all small solutes in water. (Macromolecules such as polymers behave differently because they have lots of neighbouring solvent molecules, and so affect the solvent much more than simple solutes.) So, you might expect that the antifreeze in a radiator not only stops it freezing, but also helps stop it from boiling. However, the real situation is more complicated: antifreeze has the disadvantage that it is not quite so good at transporting heat. Ethylene glycol is one antifreeze. Salt is used to melt snow and ice on roads in cold countries, but it is not used in radiators because it is corrosive and crystallises readily. Sugar is not used in some applications, because concentrated sugar solutions are viscous, and because they support bugs. However, many organisms use sugars and other small organic molecules as antifreeze.

Pure water at 1 atm will freeze at 0C or 32F. When something is dissolved in it the freezing point drops to a lower temperature. This is why when roads are salted there are puddles even though the temperature is below freezing. The more salt the lower the temperature must go before it freezes.

Source: http://www.phys.unsw.edu.au/~jw/boiling.html#solutes

Procedure:

1. Pour 20 mL of water into four testubes 2. One testube is the controll- leave it water. The other three test tubes have different amounts if solute. 3. Calculate how much solute is needed for 5%, 10%, and 20% and distribute the solut into three different test tubes 4. place all four testubes in a very low temperature freezer (80 degrees celcius) 5.

Data
 * |||||||| Salt Concentration ||
 * Time || 0% || 5% || 10% || 20% ||
 * 0 min || 25 || 25 || 25 || 25 ||
 * 5 min || 5 || 0 || -3 || -4 ||
 * 10 min || 2 || -2 || -5 || -9 ||
 * 15 min || 0 || -3 || -7 || -10(salt) ||
 * 20 min || -1 || -4 || -10 (salt) || -10 ||
 * 25 min || -2 || -7 || -10 || -11 ||
 * Liquid phase || 0 ml || 0.09 ml || 0.36 ml || 2.87 ml ||
 * Liquid phase || 0 ml || 0.09 ml || 0.36 ml || 2.87 ml ||


 * Time ||  ||   ||   ||   ||

clusion: