Learn vocabulary, terms, and more with flashcards, games, and other study tools. The pdb for your graph stands for paradichlorobenzene. Determination of molar mass by freezing point depression lab. In todays experiment, you will explore the changes in freezing point behavior of solutions in which tbutyl alcohol 2methyl2propanol is the solvent. Determination of molar mass by freezing point depr. Freezing point depression of lauric acid reading assignment. Molar mass by freezing point depression continued 2 21 flinn cientiic inc all ights esered 5a1. The unknown molar mass was calculated to be on average 96. Once we know the value of the freezing point depression constant for cyclohexane, we can use it to determine the molar mass of an unknown molecular solute. Chm112 lab molar mass by freezing point depression grading rubric criteria points possible points earned lab performance printed lab handout and rubric was brought to lab 3 safety and proper waste disposal procedures observed 2 followed procedure correctly without depending too much on instructor or lab partner 3. What was the mass of water used in this experiment. Determination of the molar mass of an unknown solid by freezing point depression goal and overview in the rst part of the lab, a series of solutions will be made in order to determine the freezing point depression constant, k f, for cyclohexane. The molality, m, of a solution can be expressed in terms of the molar mass of the solute.
Determination of molar mass by freezing point depression page 5 of 6 5. The temperature remains constant as a pure liquid freezes only if the solid and liquid are. Application of the generalized clapeyron equation to freezing point. Molecular mass by freezing point depression kyle miller november 28, 2006 1 purpose the purpose of this experiment is to determine the molecular mass of organic compounds which are dissolved in a solvent by noting the depression in the freezing point of the solution. When the composition is expressed as a molality, the proportionality constant is known as the cryoscopic constant k f and is characteristic for each solvent.
Start studying molecular mass by freezing point depression lab. Determination of molar mass by freezingpoint depression pdf. One of the uses of colligative properties is to determine the molar mass of an unknown substance. View lab report post lab 1 determining freezing point depression in naphthalene. Use uppercase for the first character in the element and lowercase for the second character. Here, k f is the molal freezing point depression constant that is characteristic of the solvent. Exercise 1 determination of molar mass from freezing point.
Properties based only on the number of solute particles and not their identity are known as colligative properties. Freezing point depression is a colligative property observed in solutions that results from the introduction of solute molecules to a solvent. Determining molar mass by freezingpoint depression. Colligative properties and determination of molar mass. Chm112 lab molar mass by freezing point depression. The freezing point of a solution is lower than that of the pure solvent, and the freezing point depression. Thus, a plot of the change in freezing point versus the molality of all various waterglycerol solutions should yield a straight line with a slope of k f. Molar mass by freezing point depression purpose the purpose of this experiment is to determine the molar mass of an unknown substance by measuring the freezing point depression of a solution of the unknown with bht. In this experiment, you will determine the freezing point of cyclohexane and the freezing point of a solution containing a weighed amount of unknown solute and. Test tube, 18150 millimeters wire stirrer weighing dish timer, seconds chemicals. The freezing points of solutions are all lower than that of the pure solvent and is directly proportional to the molality of the solute. The goal of this lab is determine the freezing point depression constant k f for tbutanol and determine the molar mass of a solute by measuring the freezing point depression of tbutanol when that solute is added to it.
Molar mass and freezing point depression lab prep key points it is the number of solute particles, not their identity, which determines the magnitude of the boiling point elevation and freezing point depression. The colligative property of freezing point depression was the theory at work behind what was observed in the experiment trials. How does the freezing point measured for water compared to what you expected. This experiment focuses on the property of freezingpoint depression. This is the procedure, and an overview of the calculations. Molal freezing point depression constants of several solvents solvent kfreezing point, c f, c. The freezing points of these solutions, which will contain known amounts of pdichlorobenzene dissolved in cyclohexane, will be measured. From the freezing point depression of lauric acid we can determine the molar mass of benzoic acid. T is the freezing point depression, kf is the freezing point depression constant for a particular solvent 1. Freezing point depression occurs when a solute is added to a solvent producing a solution. Lab 7 determination of the molar mass of an unknown solid by freezing point depression goal and overview in the first part of the lab, a series of solutions will be made in order to determine the freezing point depression constant, k f, for cyclohexane. Determination of the molar mass by freezing point depression experiment. Molar mass by freezing point depression introduction when a nonvolatile solute is dissolved in a solvent, the freezing point of the solution is lowered.
The molar mass is an important value that must be known in order to identify an unknown substance or to characterize a. As the temperature of the water bath reaches the melting point of thepdb, it will begin to melt. In this experiment, the freezing point depression of stearic acid after adding an unknown fatty acid was determined. Molar mass by freezing point depression lab question. Chm112 lab molar mass byfreezing point depression gradingrubric criteria points possible points earned. Energy is neither created nor destroyed, but only transformed from one form to another. At what temperature did the solution of fp sample 2 freeze. After most of the solid pdb appears to have melted, insert the glass stirrer and.
Determination of the molar mass by freezing point depression. When a solution forms, the freezing point of the solution is lower than the freezing point of the pure solvent. Even though the freezing point of butylated hydroxytoluene is known, it. To be able to use these properties to determine the molar mass of a substance. Putting the value of molality in above equation we get depression in freezing point as. Hence, we can use depression of freezing point to evaluate molar mass of solute.
Goals we will measure the freezing point depression of lauric acid that takes place with the addition of benzoic acid. Freezing point depression and molar mass objectives. The objective of this experiment is to determine the molar mass of an unknown solute by measuring the freezing point depression of a solution of this solute in a solvent as compared to the freezing point of the pure solvent. Molar mass by freezing point depression november 28, 2012 name lab partner purpose. Lab 7 determination of the molar mass of an unknown solid by. The freezing point of the pure solvent will be found first. Molar mass by freezing point depression essay 657 words. Determination of molar mass by freezing point depression in this experiment you will determine the molar mass of an unknown by determining the freezing point depression of the solvent, lauric acid, by adding the solute, the unknown. T f, or the degrees by which the freezing point of the solution is lower than the freezing point of the pure solvent, can be calculated by eqn. Molar mass by freezing point depression objectives. Take home freezing point depression lab page freezing point depression takehome lab continued 3. Using your data table as a guide, combine 1 drop of the solution.
From the data, the molar mass of the solute can be calculated and used to identify the unknown. Next, the freezing point of the benzoic acid and dodecanoic acid solution will be measured. Determination of the molar mass of an unknown solid by. Nick boyea billy lee 3911 molar mass by freezing point depression overview the purpose of this lab is to measure the freezing point depression of a solution of an unknown substance and bht to determine the molar mass of the unknown substance. It will calculate the total mass along with the elemental composition and mass of each element in the compound.
Molar mass by freezing point depression ap chemistry. Deliver the liquid to the beaker and find the mass of the beaker and the liquid. Molecular weight of a water soluble solid unknown by. For a sketch, one may simply combine a rising v graph horizontal parabola and. Measure the freezing point of pure water lab results 1. Youve just watched joves introduction to using freezing point depression to determine the identity of an unknown compound. In the first part of the lab, a series of solutions will be made in order to determine the freezing point depression constant, kf, for cyclohexane. Molar mass by freezing point depression lab essay 602 words. Determination of molar mass by freezingpoint depression.
These include freezing point depression, osmotic pressure, and boiling point elevation. Freezingpoint depression to determine an unknown compound. Derivation of freezingpoint depression from chemical potential. The freezing point of the solvent was lowered by the addition of the nonvolatile solute to the cyclohexane solvent. Summary of lab procedure if not already completed, crush a small amount of bht and pack it into a capillary tube.
Find the molar mass of a solute by the method of freezing point depression evaluate the accuracy of the method by comparison to a molar mass calculated from a molecular formula. How would each affect the calculated molar mass of the solute too high, too low, no effect. The freezing points of these solutions, which will. Background there are a number of ways of determining the molar mass of a substance. Molecular mass by freezing point depression short answers.
Colligative properties determination of the molar mass of a compound by freezing point depression. Experiment 20 freezing point depression lab manuals for. Molecular mass by freezing point depression lab quizlet. You should now understand the phenomenon of freezing point depression, the relationship between freezing point depression and the molar mass of the solute, and why the phenomenon is useful to a variety of industries. The following errors occurred when the above experiment was carried out. Post lab 1 determining freezing point depression in. From the graph i determined the freezing point of t butanol as 23 c. In the second part of the experiment, the molar mass of an unknown substance must by determined by. Molar mass by freezing point depression short answer experiment 1. T is directly proportional to the amount concentration for dilute solutions. Molar mass by freezing point depression lab video explanation duration. Freezing point depression is a colligative property in which the freezing temperature of a pure solvent decreases in proportion to the number of solute molecules dissolved in the solvent. By knowing the masses of the benzoic acid and the dodecanoic acid, by measuring the freezing point depression, the molality of the solution and the molar mass of benzoic acid can be calculated. This process is called freezing point depression and is a colligative property of solutions.
K f is the molal freezing point depression constant whose value depends only on. The molal freezing point depression constant for h2o, kf, is given as 1. Molecular weight determination chemistry libretexts. The known mass of the added solute and the freezing point of the pure solvent information permit an accurate calculation of the molecular weight of the solute. Exercise 1 determination of molar mass from freezing point depression colligative properties the properties we now consider are the lowering of vapour pressure, the elevation of boiling point, the depression of freezing point, and the osmotic pressure arising from the presence of a solute. Temperature is a measure of the average kinetic energy of atoms and molecules. Determination of molecular weight by freezing point depression. To determine the molar mass of an unknown substance by measuring the freezing point depression of a solution of an unknown substance and bht.
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