In general, freezing point depression is a colligative property that describes a process in which the solute causes a solution to have a lower freezing point than the pure solvent. Test tube, 18150 millimeters wire stirrer weighing dish timer, seconds chemicals. Molar mass by freezing point depression ap chemistry. 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. Determination of molar mass by freezing point depression chem. In this experiment, pure lauric acid and a mixture of lauric acid and benzoic acid were compared and analyzed. Now you need to find the moles to complete the problem. Molar mass determination by depression of freezing. Jun 30, 20 using the collected data, we used the change in freezing point and the freezing point constant for pure water 1.
Determine the moles of unknown the solute from the molality of the solution and the mass of solvent in kilograms used to make the solution. Molar mass by freezing point depression lab essay 602 words. Valdosta state university goal to determine the molecular mass of an unknown covalent solid by determining the freezing point depression of a solution. In todays experiment, you will explore the changes in freezing point behavior of solutions in which tbutyl alcohol 2methyl2propanol is the solvent. First, the freezing point of the pure solvent had to be determined and so if some of the solvent was on the walls of the test tube opposed to in the solution how would this affect. The work described herein incorporates dsc to determine the molar mass of an unknown by freezing point depression. Please check if delta tf or molality of t butanol solution is correct. The freezing point depression can be determined by subtracting the temperature of the solution by the temperature of the water. The freezing point depression can be readily explained from the theory of phase equilibria in. 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. Youve just watched joves introduction to using freezing point depression to determine the identity of an unknown compound.
Molar mass determination by depression essay example for free newyorkessays database with more than 65000 college essays for studying. 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. The apparatus for depression of the freezing point consists of two cylindrical glass vessels, arranged concentrically and connected with a gl 45 screw. The freezing point of the pure solvent will be found first. Molar mass by freezing point depression objectives. Determine the molar mass from the mass of the unknown and the number of moles of. In this laboratory, we will find the molar mass of an unknown substance that was combined with bht using freezing point depression. The magnitude of this depression depends on the concentration of solute particles in the solution, not the identity of the solute. When a solution forms, the freezing point of the solution is lower than the freezing point of the pure solvent. The depression in freezing point is another colligative property of solutions that gives us a method to determine the molar masses of various substances similar to elevation of boiling point. Conclusion the purpose of this experiment was to determine. This decrease is proportional to the molal concentration of the solute. Some other useful solvents and their freezing point constants are listed below.
October 6, 2016 2 introduction molar masses or formula masses are important quantities. Calculate and enter the freezing point depression of a solution of 80. The molar mass is an important value that must be known in order to identify an unknown substance or to characterize a. Experiment 14 mole unit molar concentration scribd. Molar mass determination by depression essay sample. The molar mass of an unknown fatty acid was by found by getting the difference between the freezing points of pure stearic. Determine the molar mass of an unknown solute using data from the proceeding. The relationship between the lowering of the freezing point and the concentration of the solution is given by the following. The relationship between the molar concentration and the freezing point depression is that the freezing point depression is the multiplication of molar mass and cant hoff ifactor. The molar mass would be lower because if the freezing point was 0.
Determine the apparent molar mass of a nonelectrolyte hydroquinone from the value of freezing point depression. If the freezing point of the solution had been incorrectly read 0. Dissolving nonvolatile substance in a solvent lowers the freezing point of a solvent. Molecular weight of a water soluble solid unknown by. Freezing point depression an overview sciencedirect topics. Exercise 1 determination of molar mass from freezing point. Show the calculation of the freezing point of a solution made by dissolving 12. From the graph i determined the freezing point of t butanol as 23 c. Experiment 14 determination of molar mass by freezing point depression.
Determination of the molar mass of an unknown solid by. That is, increasing the molar or molecular mass will have a smaller effect on the freezing point. Atf is called the freezing point depression, which is the change in freezing point. You know the freezing point depression of the solution and the cryoscopic constant, so you can calculate the molality. A determination of the freezing point of naphthalene. Molecular weight of a water soluble solid unknown by freezing. Freezing point depression follows the colligative laws of thermodynamics at low concentrations added to water. The freezing points of these solutions, which will contain known amounts of pdichlorobenzene dissolved in cyclohexane. In petroleum engineers guide to oil field chemicals and fluids second edition, 2015. Aug 24, 2016 thus, as the molar mass increases, the freezing point depression decreases. Freezing point depression and molar mass objectives.
Molar mass determination from freezing point depression previously, compounds such as pdichlorobenzene, biphenyl, benzil, and. This lab replaces traditional experiments using hazardous organic solvents. Freezing point of a solution of liqud unknown freezing point depression. Find the molar mass of a solute by the method of freezingpoint depression evaluate the accuracy of the method by comparison to a molar mass calculated from a molecular formula. Setup and procedure perform the experimental setup shown in figure 1. In this video we will learn how to determine the molar mass of an unknown solute but using the freezing point depression of the solution. Chemistry 1210 determination of molar mass by freezing point. The freezing points of these solutions, which will. Molal freezing point depression constants of several solvents solvent freezing point, c kf, c. Jan 22, 2011 prelab video for the determination of molar mass by freezing point depression experiment in chem 210l, general chemistry ii, at minnesota state university moorhead.
To determine the molar mass of a substance by freezingpoint depression. Determine the molar mass from the mass of the unknown and the number of moles of unknown. Molecular mass by freezing point depression lab by av s on. The freezing point depression is based on the molal concentration moles of solute per kg of solvent. Molar mass by freezing point depression lab video explanation. The molar mass of an unknown fatty acid was by found by getting the difference between the freezing points of pure stearic acid and the mixture of stearic.
Determination of molar mass by freezing point depression camphor melts at 179. This document is the lab report from the freezing point depression and colligative properties experiment. The unknown is a nonelectrolyte and nonvolatile substance. Molar mass by freezing point depression september 16, 2014 abstract the experiment aimed to determine the molar mass of an unknown substance by finding its freezing point depression. It depends on the ratio of solute and solvent particles and not on the nature of the. Determination of molar mass by freezing point depression. Lets become familiar with colligative properties and to use them to determine the molar mass of a substance you need this equipment. Molar mass determination from freezing point depression previously, compounds such as pdichlorobenzene, biphenyl, benzil, and naphthalene were used. Like atomic masses, these values are the foundation for the majority of numerical work when it comes to chemistry.
A free powerpoint ppt presentation displayed as a flash slide show on id. 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. Freezing point depression lab report 3 dipaly bhakta. The molal freezing point depression constant for h2o, kf, is given as 1. Calculating molar mass using freezing point depression on vimeo. In this experiment, freezing point depression was used to study the molar mass of an unknown substance. Molar mass determination by freezing point depression. Calculating the molar mass of a solute from freezing point. Calculate the molal freezing point depression constant kf for the solvent. Students determine the molar mass of an unknown fatty acid dissolved in a known fatty acid using freezing point depression and colligative properties. Molar mass is useful to identifying an unknown substance.
To be able to use these properties to determine the molar mass of a substance. Valdosta state university goal to determine the molecular mass of an unknown covalent solid by determining the freezing point depression of a solution valdosta state university background colligative properties. In this experiment, you will determine the molar mass of an unknown solute. The following data was obtained in an experiment designed to find the molar mass of a solute by freezing point depression.
Molecular mass by freezing point depression darlene dsouza, nithya mitta, ashwini parchure, avni shah prelab 2. 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 size of freezing point depression depends on two things. Determine the change in freezing point from the observed freezing point of the solution and the freezing point of the pure solvent. Determining molar mass of unknown using freezing point. Molal freezing point depression constants continued 2 21 flinn cientific nc ll igts esere for a 0. Freezingpoint depression to determine an unknown compound. The freezing point depression of a solution of nitrobenzene and a nonionic unknown was used to determine the molar mass of the unknown. Determination of molar mass by freezing point depr. Determining molar mass by freezing point depression.
Nov 29, 2006 so we did an experiment of freezing point depression and my calculated molar mass values were larger than actual. The freezing point depression is directly related to the number of moles of particles per kilogram of water. 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. When a solute is dissolved in a solvent, the temperature at which the solvent freezes decreases. K f is the molal freezing point depression constant whose value depends only on the solvent.
Freezing point depression occurs when a solute is added to a solvent producing a solution. Determination of molecular weight using colligative properties. The apparatus for depression of the freezing point consists of. Jul 30, 20 the molar mass of the unknown compound is 88. Determination of molar mass by freezing point depression 1 if a particular solvent has a freezing point depression constant of 5. Nelson, 2015 introduction a solution consists primarily of solvent, the major component, and therefore, most. Molecular mass by freezing point depression lab by av s on prezi. Determination of molar mass by freezing point depression lab. Background there are a number of ways of determining the molar mass of a substance. Molar mass from boiling point elevation or freezing point.
Properties based only on the number of solute particles and not their identity are known as colligative properties. T is the freezing point depression, kf is the freezing point depression constant for a particular solvent, and m is the molality of the solution. 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. Using the molality and the masses noted in steps 1 and 2 27. The freezing point depression or change in freezing point is given by t f k f m where t f t f t f 1 t f is the freezing point of the solution in c and t f is the freezing point of the pure solvent, also in c. Determining molecule weight by freezing point depression. As these compounds are toxic and therefore potentially hazardous, they have been replaced with naturally occurring nontoxic fatty acids. One use of colligative properties is the determination of the molecular weight of a. Lab 7 determination of the molar mass of an unknown.
In this experiment, we will investigate the phenomenon of freezing point depression and determine the molar mass of substance x. Cyclohexanol, c 6 h 11 oh, is sometimes used as the solvent in molar mass determination. Jul 02, 2014 the freezing point depression, or the difference between the freezing points of the pure solvent and solution, depends upon the number of particles in solution. At the same time, the boiling point generally will be increased. Determine the change in boiling or freezing point temperature solution and pure solvent. Lab 7 determination of the molar mass of an unknown solid. To determine the molar mass of an unknown substance by measuring the freezing point depression of a solution of an unknown substance and bht. Molal freezing point depression constants scientific. Molar mass determination from freezing point depression when a nonvolatile solute is dissolved in a solvent, the solvents boiling point is increased, its freezing point is decreased, and its osmotic pressure is increased. Cryoscopic determination of molar mass free download as powerpoint presentation. Determination of molar mass by freezing point depression freezing point depression is one of the colligative properties, properties that depend on the concentration number of particles and not the identity of a solute.
Calculating the molar mass of a molecular substance from its freezing point depression. The purpose of this experiment was to determine the molar mass of an unknown, nonvolatile solute. Next, the freezing point of the benzoic acid and dodecanoic acid solution will be measured. Molar mass determination from freezing point depression. Molar mass by freezing point depression november 28, 2012 name lab partner purpose. The freezing point depression is one of the colligative properties of a solution. Freezing point depression free download as pdf file. Dipaly bhakta 02172015 freezing point depression abstract the purpose of the experiment was to use the concept of freezing point depression to determine the molar mass of a compound by determination of the freezing point of a pure solvent and a solution. 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. Compare freezing points of a pure solvent and a known solution of the solvent to determine the change in freezing point, tf. Determination of molar mass by freezingpoint depression. A short lesson on how to calculate the molar mass of a substance from freezing point depression data. Introduction of differential scanning calorimetry in a.
Cyclohexane is used as the pure solvent and the molal freezing point depression constant, kfp, is determined with. The main aim of this experiment is to determine the molar mass of an unknown using freezing point depression of a known solvent and from experimental data. One of the uses of colligative properties is to determine the molar mass of an unknown substance. Show the calculation of the freezing point of a solution. Ask your teacher if your unknown compound dissociates, and, if so, how many ions are contained in a single formula unit. 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. The cooling curves for the solutions were generally accurate, and resulted in a realistic molar mass, which means this lab was a success. Colligative properties determination of the molar mass of a compound by freezing point depression.
Determine the molal concentration, m, from the change in freezing point and the freezing point depression constant. 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. Kf molal freezing point depression constant in c kgmol. Help with freezing point depression error analysis. These include freezing point depression, osmotic pressure, and boiling point elevation. Determine freezing point depression constant for pure. Jun 05, 2011 molar mass by freezing point depression november 28, 2012 name lab partner purpose. Molar concentration is the number of moles in a solute divided by the mass.
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