Determining the molecular weight of an unknown compound using cyclohexane
Sample calculation. The solute will not enter the solid phase because the incorporation of solute molecules into the crystal structure of the solid solvent is usually energetically unfavorable. This keeps impurities the solute out of the solid phase as the liquid freezes.
Freezing point of pure cyclohexane
Save the data. The phenomenon of freezing point depression has many applications both inside and outside the laboratory. The measured freezing point change will be used to calculate the molar mass of the unknown solid. A solution prepared by dissolving 1. Occasionally, it is possible to take advantage of the freezing-point depression phenomenon to eliminate the need for a solvent in a synthesis. Of the five options provided for this experiment, naphthalene is the closest match. Make a new ice-water bath. Determination of the Molecular Weight of an Unknown Compound 1.
In this solution, the freezing point of water is lowered by 2 x 1. You can use two cups, one inserted inside the other, for better insulation, and you may want to place the cups in a beaker or mL for better support.
Freezing point depression lab answers
At equilibrium, the number of molecules leaving and entering the solid phase per unit time are equal. What was the objective of this experiment and how was it achieved? Measuring the Freezing Point of Cyclohexane Dispense To prevent supercooling, steady stirring of the liquid is required. It also can be more accurately measured since the boiling point is more sensitive to atmospheric pressure changes than the freezing point. This phenomenon results from interactions between the solute and solvent molecules. Insert the test tube deep into the ice bath, carefully stirring the solution continuously with the thermometer, and record the temperature every 30 seconds on the data sheet. Freezing point depression is a colligative property, meaning it is only affected by the ratio of solute to solvent particles, and not their identity. Chemists exploit the phenomenon of freezing-point depression in the analysis of solid organic compounds.
At the freezing point, the kinetic energy of the particles becomes low enough for inter-particle forces to lock the particles into fixed positions in the solid crystal structure. The molar mass of the solute, and therefore the identify of the solute, can be determined from the relationship between the freezing point of the pure solvent, the freezing point of the solution, and the molality of the solution.
Insert the stopper with the temperature probe and wire stirrer into the test tube. The temperature of the system the freezing liquid remains at the freezing point until all of the liquid has frozen. Glacial acetic acid has a freezing point of Add 12 mL of cyclohexane to a clean, dry test tube.
When the salt mixes with the ice, the freezing point of the water is depressed so the ice melts at a lower temperature.
Determination of molecular weight by boiling point elevation
In a beaker, prepare an ice water bath. Because the degree of the freezing point depression is dependent on the number of particles in solution, salts that release three ions per formula unit, such as calcium chloride CaCl2 , are often utilized for this purpose. How many grams of ethylene glycol, C2H5 OH 2, must be dissolved in Freezing point depression is a colligative property, meaning it is only affected by the ratio of solute to solvent particles, and not their identity. Continue collecting data until the slope of this decrease is evident. The values of the freezing point of the pure solvent and the freezing point of the solution are determined from the plots. What safety rules must be observed during this experiment? The freezing point method is more practical because of the greater temperature interval involved. Make sure the tip of the temperature probe is in the center of the liquid and not touching the sides or bottom of the test tube. Once the liquid has completely frozen, only then will the temperature start to fall again.
The freezing point depression constant for cyclohexane Kf is Preparing a Solution of the Unknown Compound Accurately weigh 0. One mole or 6.
based on 54 review