These include freezing point depression, osmotic pressure, and boiling point elevation. Calculate and enter the freezing point depression of a solution of 62. Apparatus for freezing point determination dry the testtube set in oven prepare. Nov 29, 2006 so we did an experiment of freezing point depression and my calculated molar mass values were larger than actual. Molecular weight of a water soluble solid unknown by. Lab 7 determination of the molar mass of an unknown solid by. Molecular weight of a water soluble solid unknown by freezing. 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. Freezing point depression the size of the freezing point depression depends on two things. Molar mass from boiling point elevation or freezing point.
Calculate and enter the freezing point depression of a solution of 80. 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. Previously, compounds such as pdichlorobenzene, biphenyl, benzil, and naphthalene were used. Now you need to find the moles to complete the problem. Molar mass determination by depression essay sample. Observing and measuring the effect of solute on freezing point of the solvent was conducted, and. 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. Hot platemagnetic stirrer plastic beaker 1 l glass rod. From the graph i determined the freezing point of t butanol as 23 c. Prelab video for the determination of molar mass by freezing point depression experiment in chem 210l, general chemistry ii, at minnesota state university moorhead.
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. The purpose of implementing this procedure is to reduce waste and use less toxic materials. You know the freezing point depression of the solution and the cryoscopic constant, so you can calculate the molality. Determine the change in freezing point from the observed freezing point of the solution and the freezing point of the pure solvent. The molar mass would be lower because if the freezing point was 0. In principle, the boilingpoint elevation and the freezingpoint depression could be. 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. 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 boilingpoint elevation and freezing point depression. In this experiment, the purpose of this was to determine the molar mass of a nonvolatile, nonelectrolyte solute using the freezing point depression. 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. 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. Determining molar mass of unknown using freezing point.
There are various methods for obtaining the molar mass. In todays experiment, you will explore the changes in freezing point behavior of solutions in which tbutyl alcohol 2methyl2propanol is the solvent. The magnitude of this depression depends on the concentration of solute particles in the solution, not the identity of the solute. Valdosta state university goal to determine the molecular mass of an unknown covalent solid by determining the freezing point depression of a solution. A greener approach for measuring colligative properties. This experiment focuses on the property of freezingpoint depression. Molar mass by freezing point depression lab essay 602 words. In this experiment, pure lauric acid and a mixture of lauric acid and benzoic acid were compared and analyzed. Stir the solventsolute mixture in the large test tube and repeat the determination of the cooling curve. Calculating the molar mass of a solute from freezing point.
Freezing point depression and molar mass experiment 17 174 one can now use equation 17. Molecular mass by freezing point depression darlene dsouza, nithya mitta, ashwini parchure, avni shah prelab 2. One of the uses of colligative properties is to determine the molar mass of an unknown substance. 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. 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. Use a 10 ml graduated cylinder with cork to measure between 0. 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. In general, freezing point depression is a colligative. 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. This document is the lab report from the freezing point depression and colligative properties experiment. T05 freezing point depression and molar mass determination 20809 revised.
Chemistry 1210 determination of molar mass by freezing point. Molar mass by freezing point depression objectives. Cryoscopic determination of molar mass solution melting point. If the freezing point of the solution had been incorrectly read 0. The molar mass is found by dividing the mass of the solute, in grams, by the number of moles. Determine the apparent molar mass of a nonelectrolyte hydroquinone from the value of 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. This property, known as freezingpoint depression, is a colligative property.
The apparatus for depression of the freezing point consists of two cylindrical glass vessels, arranged concentrically and connected with a gl 45 screw. Experiment 14 mole unit molar concentration scribd. 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. T05 freezing point depression and molar mass determination 20809 revised 2. Setup and procedure perform the experimental setup shown in figure 1.
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. Jul 30, 20 the molar mass of the unknown compound is 88. To address those concerns, this lab uses an aqueous solution of a green compound sucrose, c 12 h 22 o 11, 342 gmole for determining its molar mass by the freezingpoint depression of water. 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. 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. Determination of molar mass by freezingpoint depression. The molal freezing point depression constant for h2o, kf, is given as 1.
You will then add a known mass of an unknown solute to a known mass of ps, and determine the lowering of the freezing temperature of the solution by. Freezingpoint depression is the decrease of the freezing point of a solvent on the addition of a. Determine the molar mass from the mass of the unknown and the number of moles of unknown. 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. 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. The size of freezing point depression depends on two things. Molar mass determination by freezing point depression. Statistical treatment of data of this lab manual, calculate the means, the standard. This experiment focused on determining the molar mass of an unknown substance. In this experiment, we will first measure the freezing point of pure naphthalene, then. T is the freezing point depression, kf is the freezing point depression constant for a particular solvent 1. This lab replaces traditional experiments using hazardous organic solvents.
Waste disposal dispose of all cyclohexane solutions in the waste container in the hood. And the molal concentration of the solution which depends on the number of moles of solute and the kg of solvent. Exercise 1 determination of molar mass from freezing point. When a solution forms, the freezing point of the solution is lower than the freezing point of the pure solvent. The freezing point depression is based on the molal concentration moles of solute per kg of solvent. These characteristics of a solution are termed the colligative properties. Calculating molar mass from freezing point depression. 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. Determine the change in freezing point from the observed freezing point of the solution and the freezing point of. In the experiment, the molar mass of the unknown solid was determined by the freezing point of the benzene and the freezing point depression of the solution when the unknown was added, data and results. Molar mass determination by depression of freezing. T05 freezing point depression and molar mass determination. Freezing point depression free download as pdf file. The degree of dissociation is measured by determining the van t hoff factor i by first.
Please check if delta tf or molality of t butanol solution is correct. 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. Test tube, 18150 millimeters wire stirrer weighing dish timer, seconds chemicals. The purpose of this experiment was to determine the molar mass of an unknown, nonvolatile solute. The cooling curves for the solutions were generally accurate, and resulted in a realistic molar mass, which means this lab was a success. Caddell depressing the freezing point of cyclohexane in this lab you will determine the molar mass of an unknown by determining the freezing point depression of a sample of cyclohexane after dissolving your unknown in the cyclohexane. Jul 20, 2009 molar mass determination by freezing point depression. Thus, as the molar mass increases, the freezing point depression decreases. K f is the molal freezing point depression constant whose value depends only on the solvent. 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. Properties based only on the number of solute particles and not their identity are known as colligative properties. Molar mass is useful to identifying an unknown substance. Using freezingpoint depression to find molecular weight.
Jun 05, 2011 molar mass by freezing point depression november 28, 2012 name lab partner purpose. Molar mass by freezing point depression introduction when a nonvolatile solute is dissolved in a solvent, the freezing point of the solution is lowered. From the freezing point depression of lauric acid we can determine the molar mass of benzoic acid. In addition, there is a slow gradual fall in temperature as freezing proceeds. Kf molal freezing point depression constant in c kgmol. This process is called freezing point depression and is a colligative property of. Experiment 14 determination of molar mass by freezing point depression. Determination of the molar mass of an unknown solid by.
Determination of molar mass by freezing point depr. Freezingpoint depression to determine an unknown compound. Freezing point depression occurs when a solute is added to a solvent producing a solution. The temperature at which a solution freezes is lower than that for the pure solvent.
Molal freezing point depression constants of several solvents solvent freezing point, c kf, c. The molecular weight of this unknown compound can be determined by observing the freezing point of a solution of. Background there are a number of ways of determining the molar mass of a substance. Determination of molecular mass by freezing point depression page 3 of 10 the cooling behavior of a solution is somewhat different from that of a pure liquid see figure 2. Calculating the molar mass of a molecular substance from its freezing point depression. Using freezingpoint depression to find molecular weight lab free download as word doc. Freezing point of a solution of liqud unknown freezing point depression. Jul 22, 2016 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. Determination of molar mass by freezing point depression lab.
Determination of molar mass by freezing point depression. Students determine the molar mass of an unknown fatty acid dissolved in a known fatty acid using freezing point depression and colligative properties. A greener approach for measuring colligative properties student directions molar mass determination from freezing point depression this is a new procedure. In this experiment, freezingpoint depression was used to study the molar mass of an unknown substance. The molar mass of an unknown fatty acid was by found by getting the difference between the freezing points of pure stearic. Molar mass by freezing point depression november 28, 2012 name lab partner purpose. Determination of molar mass by freezing point depression chem. That is, increasing the molar or molecular mass will have. 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. The size of the k f for a given solvent, which are well known. In this laboratory, we will find the molar mass of an unknown substance that was combined with bht using freezing point depression.
Molar mass by freezing point depression ap chemistry. Determine the change in boiling or freezing point temperature solution and pure solvent. The freezing point depression can be determined by subtracting the temperature of the solution by the temperature of the water. Determination of molecular mass by 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. Lets become familiar with colligative properties and to use them to determine the molar mass of a substance you need this equipment.
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. The molar mass is an important value that must be known in order to identify an unknown substance or to characterize a. Molecular mass by freezing point depression lab by av s on prezi. In this experiment, freezing point depression was used to study the molar mass of an unknown substance. Determination of molar mass by freezing point depression camphor melts at 179. Use freezing point depression to calculate molar mass of an unknown solute. This was done by determining the freezing point of lauric. Lab 7 determination of the molar mass of an unknown solid. Calculate and enter the freezing point depression of a solution of 61. Repeat step 3 to obtain a fresh sample of tbutanol. The freezing points of these solutions, which will. You will determine the molar mass of the unknown solute based on the decrease in the freezing point.
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