Colligative properties PDF

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Name: Experiment 3 Colligative Properties Instructor: Jessica Harris Colligative Properties Introduction Colligative properties are properties of solutions that does not depend on what type of nonvolatile solute are presence in solution but rather depend on the number of particles (or solute) dissolve in solution. These colligative properties include vapor pressure, boiling point, freezing point, and osmotic pressure. When nonvolatile solute is added, solute particles interfere with the ability of the solvent particles to vaporize, thus vapor pressure of concentration solution is lower than solvent solution. This lower vapor pressure leads to boiling point elevation due to the addition of solute because it requires more energy to absorb in order to cause the vapor pressure to equal atmospheric pressure. Similarly, adding a nonvolatile solute to solvent solution decrease the temperature and the liquid of solvent slowly form a solid, resulting in lower freezing point. Therefore, the freezing point of concentration solution is lower than the freezing point of the solvent solution. Osmotic pressure is a pressure that apply to the solution to prevent the flow of water crossing the membrane. In this experiment, the boiling point elevation of constant water is examined by using a solution of sodium chloride and ethylene glycol. From observation during experiment, calculation is needed to find kb (boiling point elevation), molar mass of ethylene glycol, and molar mass of unknown solid.

Results Kb = 0.71 degrees celsius per molality Molar mass of ethylene glycol = 22.3 grams Molar mass of Unknown solid = 38.34 grams Percent error = 39.22 % Mass of NaCl: 30.4 grams Mass of ethylene: 51.0 grams Mass of unknown: 39.7 grams Table Temperature

Temp. Calibration

Boiling point of Water

100 degrees Celsius

100 C

Boiling point of NaCl

105 degrees Celsius

105 C - 100 C = 5 C

Boiling point of ethylene

105 degrees Celsius

105 C - 100 C = 5 C

Boiling Point of unknown solid

105 degrees Celsius

105 C - 100 C = 5 C

Discussion The main theory of colligative property experiment is the idea of boiling point elevation. As mentioned in above, boiling point elevation is defined as higher boiling point when boiling point is higher than normal boiling point, such as water, at 100 degrees celsius. In this

experiment, the experiment is done in four different session with similar procedure. First, only pure solvent solution or water is heat to measure temperature at boiling point and its use as a control to compare with others three experiment. This boiling point occur at 100 degree celsius. Second part of lab session is done by mixing together of 30.4 grams of sodium chloride and 146.47 grams DI water. Boiling point occurs as expected at 105 degree celsius because its expected to be higher boiling point than the pure solvent since it requires more energy in order to boil. Then, boiling point elevation formula is used to find boiling point elevation constant, Kb, for water. The calculation resulting as 0.71 degree celsius per molality, however, normal boiling point elevation constant is 0.51 degree celsius per molality. The reason why boiling point constant resulting as high number is that because the weight of water is much lower than compared to actual given weight of water. For example, 150 grams of DI water is expected to be mixed with 30 grams of sodium chloride which then can be result around 0.51 Kb. However, the weight that had been used in the experiment is only 146.83 grams of DI water. This cause Kb to be result as high number because 30. 4 grams of sodium chloride adding in 146.83 grams of water require more energy in order to occur boiling than energy that require in concentration solution of 150 grams of sodium chloride and 30 grams of water. Third, ethylene glycol and water is mix and boiling occurs at 105 degree celsius. From using 51 grams of ethylene, 97.82 grams, boiling point of ethylene glycol at 105 degree celsius, and experimentally determined value of Kb or 0.71 degree celsius per molality, the molar mass of ethylene glycol is determine which then results in 22.3 grams per moles. Also, the percent error is determined by the difference between actual value and theoretical value divided by theoretical value and multiply with 100 percent. The result of percent error is 39.22 percent. The reason percent error result as

high value percent is that because the value number of boiling point elevation constant is result as high number. Getting too high or low value number of boiling point constant compared to normal boiling point constant increase the percent error. Lastly, 39.7 grams of unknown solid is added to 146.82 grams of DI water and the boili occur at 105 degree celsius. Method used to find the molar mass of ethylene glycol is also used to find the molar mass of an unknown solid, resulting in 38.34 grams per moles.

Solution The number of particles dissolves in solution affect vaporessure lowering, freezing point depression, boiling point elevation, and osmotic pressure. In this experiment, boiling point elevation is examined with different solution; sodium chloride, ethylene glycol, and unknown solid solution. They all result in higher boiling point as expected compared to pure solvent solution....