An Analysis Of The Colligative Properties Of Freezing Point Depression

2238 Words 9 Pages
Colligative properties, or properties pertaining to solutions can be broken down into four main categories: Osmotic pressure, boiling point elevation, and freezing point depression. These three properties change drastically when in a solution compared to their values in a pure state. This is because the increased entropy leads things like a higher boiling point or lower freezing point. This lab explored the properties of freezing point depression and focused on how the freezing point was lowered when mixed with a salt and how much it was lowered when mixed with a sugar molecule. The application of freezing point depression can be seen in the real world as NaCl or table salt is typically spread out on roads so that when water falls on to the …show more content…
The normalized freezing point depression for unknown three which was -2.7 °C was divided by the product freezing point depression constant of water (1.86) and the Van’t Hoff factor which was one for both fructose and sucrose. This calculation provided the value for molality, which was 1.45 m/kg. The molality was then converted to moles by multiplying 1.45 times the kg of solvent, which was 0.02 kg. The moles were calculated to be 0.0029. The same calculation was done for unknown four where the normalized freezing point depression was -1.6 °C this was then divided by the product of the freezing point constant of water and the Van’t Hoff Factor. Once the molality of 0.860 m/kg was found it was used to convert to moles by multiplying 0.860 m/kg times the kg of solvent, which was 0.02. The number of moles was calculated to be 0.0172 for unknown three. Since the number of moles was calculated for, each unknown they could then be compared to the moles calculated using the normalized mass and molecular weights of fructose and sucrose to determine what they were. The normalized mass for part C which was 5 g was divided by the molecular weight of fructose which was 180 g, thus the amount of moles that would be present in the fructose sample would be approximately 0.027, this matched up with unknown three as it had 0.029 moles present. The moles of the sample with sucrose was found by dividing 5 g by 342 g and thus the moles present in the unknown that was sucrose would be approximately 0.014 which matched up with unknown four has it had 0.0172 moles present. Once the unknown used for experiment was known to be fructose the “theoretical” freezing point could be calculated. This was done by taking the exact mass of fructose used in the experiment of 4.9774 and dividing it by the molecular weight of

Related Documents