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. 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. 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. The work described herein incorporates dsc to determine the molar mass of an unknown by freezing point depression.
This is the procedure, and an overview of the calculations. Freezing point depression and molar mass objectives. Molar mass by freezing point depression november 28, 2012 name lab partner purpose. Molar mass by freezing point depression in this experiment, you will determine the freezing point of cyclohexane and the freezing point of a solution. Determination of the molar mass of an unknown solid by. Chm112labmolarmass byfreezing pointdepressiongradingrubric criteria pointspossible pointsearned. 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.
Molar mass determination by depression of freezing. The colligative property of freezing point depression was observed in the experimental. Determination of the molar mass by freezing point depression. 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. After most of the solid pdb appears to have melted, insert the glass stirrer and. It is a constant that is equal to the change in the freezing point for a 1molal solution of a nonvolatile molecular solute. Molar mass by freezing point depression ap chemistry. Determination of molar mass by freezing point depression chem. The proportionality constant, is called the molal freezingpoint depression constant.
Lets become familiar with colligative properties and to use them to determine the molar mass of a substance you need this equipment. Learn vocabulary, terms, and more with flashcards, games, and other study tools. The molality, m, of a solution can be expressed in terms of the molar mass of the solute. Molar mass by freezingpoint depression kit for ap chemistry. Ap chem molecular mass by freezing point depression lab. Youve just watched joves introduction to using freezing point depression to determine the identity of an unknown compound. Molecular mass by freezing point depression lab by av s on prezi.
Post lab 1 determining freezing point depression in. Determination of molar mass by freezing point depression. Lab 7 determination of the molar mass of an unknown. Molecular weight of a water soluble solid unknown by freezing. In todays experiment, you will explore the changes in freezing point behavior of solutions in which tbutyl alcohol 2methyl2propanol is the solvent. Molecular mass by freezing point depression lab quizlet.
The freezing point depression is directly related to the number of moles of particles. Molar mass by freezing point depression lab essay 602 words. Water will serve as your solvent for this experiment. Molar mass of a solid full lab report chem 10 studocu.
Im trying to determine the molar mass of an unknown substance by using freezing point. An unknown solid is to be identified from a list of possible compounds by its molar mass, which is determined by freezing point depression. In principle, the boilingpoint elevation and the freezingpoint depression. 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. 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. Freezing point depression occurs when a solute is added to a solvent producing a solution. From the freezing point depression of lauric acid we can determine the molar mass of benzoic acid. The first purpose of this lab is to determine the molecular mass of an unknown solute. Ask your teacher if your unknown compound dissociates, and, if so, how many ions are contained in a single formula unit. Determine the freezing point depression and molar mass of the unknown substance. Summary of lab procedure if not already completed, crush a small amount of bht and pack it into a. Determination of molar mass by freezingpoint depression.
Determination of molar mass by freezing point depression page 5 of 6 5. Exercise 1 determination of molar mass from freezing point. October 6, 2016 2 introduction molar masses or formula masses are important quantities. Molar mass from boiling point elevation or freezing point. View lab report post lab 1 determining freezing point depression in naphthalene. Setup and procedure perform the experimental setup shown in figure 1. Freezingpoint depression to determine an unknown compound. View lab report molar mass by freezing point depression.
The molar mass is an important value that must be known in order to identify an unknown substance or to characterize a. Pdf effects of freezing point depression on molecular weight. Molar mass determination by freezing point depression traditional experiment chemicals avoided per class of 100 students. In this experiment, the freezing point depression of stearic acid after adding an unknown fatty acid was determined. Determining molar mass by freezing point depressio. Three nonvolatile organic hydrocarbons are used as unknowns and. The purpose of this experiment was to determine the molar mass of an unknown nonvolatile nonelectrolyte solute and to observe and measure the effect of a solute on the freezing point of a solvent, cyclohexane. Determination of molar mass by freezing point depression camphor melts at 179. 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. 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. In this experiment, you will determine the molar mass of an unknown solute. This process is called freezing point depression and is a colligative property of. 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 video is part of the flinn scientific best practices for teaching chemistry video series, a collection of. Like atomic masses, these values are the foundation for the majority of numerical work when it comes to chemistry. From the data, the molar mass of the solute can be calculated and used to identify the unknown. This article is about the phenomenon caused by solutes.
To determine the molar mass of an unknown substance by measuring the freezing point depression of a solution of an unknown substance and bht. As the temperature of the water bath reaches the melting point of thepdb, it will begin to melt. Sucrose is considered a green compound for this lab because it requires no hazardous material disposal and produces no toxic fumes. The freezing points of these solutions, which will. As a result of freezingpoint depression, radiators do not freeze in winter unless it is extremely cold, e. Freezing point of a solution of liqud unknown freezing point depression. First you will determine the freezing point of pure. Temperature is a measure of the average kinetic energy of atoms and molecules. When a solution forms, the freezing point of the solution is lower than the freezing point of the pure solvent.
Energy is neither created nor destroyed, but only transformed from one form to another. Purpose the freezing point of pure tbutanol will be measured via the vernier temperature sensor. Molar mass by freezing point depression objectives. Freezingpoint depression and molar mass objectives. 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. Start studying molecular mass by freezing point depression lab. The apparatus for depression of the freezing point consists of two cylindrical glass vessels, arranged concentrically and connected with a gl 45 screw.
Determining molar mass by freezingpoint depression. I use cetyl alcohol to calculate freezing point depression constant my data from the experiment freezing point of pure bht. Freezing point depression of lauric acid reading assignment. The phenomenon of freezingpoint depression has many practical uses.
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 molal freezing point depression constant for h2o, kf, is given as 1. Freezingpoint depression is the decrease of the freezing point of a solvent on the addition of a. Chem 10 experiment 14 molar mass of solid full lab report. Molar mass of a molecular compound by freezingpoint. Molar mass of a solid full lab report chem 10 nsu studocu. Jan 22, 2011 pre lab video for the determination of molar mass by freezing point depression experiment in chem 210l, general chemistry ii, at minnesota state university moorhead.
Test tube, 18150 millimeters wire stirrer weighing dish timer, seconds chemicals. Background there are a number of ways of determining the molar mass of a substance. The freezing point depression is then used to calculate the samples molar mass. This experiment focuses on the property of freezingpoint depression. Molar mass determination by freezing point depression introduction many years ago, chemists observed that at low solute concentrations the change in the boiling point, freezing point, and vapor pressure of the solution are all proportional to the moles of solute that are dissolved in a given amount of solvent. These include freezing point depression, osmotic pressure, and boiling point elevation.
All kit materials are reusable and the kit includes a test tube rack for easy storage of freezing point samples. Molal freezing point depression constants of several solvents solvent freezing point, c kf, c. 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. Molar mass determination by freezing point depression. Free essays on molar mass by freezing point depression lab. Chemistry experiment 3 colligative properties freezing point depression. 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. When you are completely done collecting data for the day, the freezing temperature of the benzoic acidlauric acid. Tbutyl alcohol lab marquis cuffee chem 222 l 126 abstract the goals of this experiment were to determine the freezing point of tbutyl alcohol, the molal freezing point constant for tbutyl alcohol, and the molar mass of an unknown substance. 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. Using freezing point depression to find molecular weight advanced chemistry with vernier 4 3 time freezing point. Colligative properties determination of the molar mass of a compound by freezing point depression.
When a nonvolatile, nonelectrolytic solute is dissolved in a solvent, the freezing point of the solvent is lowered. The radiator fluid in an automobile is a mixture of water and ethylene glycol. Answer the pre lab questions that appear at the end of this lab exercise. The freezing points of solutions are all lower than that of the pure solvent and is directly proportional to the molality of the solute. Then use this information to find the molar mass of the unknown. Example 2 molar mass from freezing point depression the freezing point of a solution that contains 1.
Freezing point depression is a colligative property observed in solutions that results from the introduction of solute molecules to a solvent. Introduction of differential scanning calorimetry in a. The second purpose is to identify the unknown solute by finding the freezing point depression of an already known. Molecular weight of a water soluble solid unknown by. Determination of the molar mass by freezing point depression experiment. The freezing points of these solutions, which will contain known amounts of pdichlorobenzene dissolved in cyclohexane.
To determine the molar mass of an unknown soluble compound using the freezing point depression method. An optional procedure for collecting data using temperature probes is included. 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. Molecular mass by freezing point depression harry lee matt lee ap chemistry period 7 january 17, 2011 purpose. Obtain from the stockroom a lab quest 2 probe, thermal sensor, freezing point test tube fitted with a stopper, and a stirring wire. Determine the apparent molar mass of a nonelectrolyte hydroquinone from the value of freezing point depression. Molecular mass by freezing point depression darlene dsouza, nithya mitta, ashwini parchure, avni shah prelab 2.
Molar mass by freezing point depression continued 2 21 flinn cientiic inc all ights esered 5a1. Wipe the temperature probe with a lintfree wipe to be sure it is dry. Cyclohexane is used as the pure solvent and the molal freezing point depression constant, k fp, is determined with good agreement to the reported literature value. Determining molar mass of unknown using freezing point. To be able to use these properties to determine the molar mass of a substance. Wear your lab coat and safety goggles at all times during this lab. The freezing point depression can be determined by subtracting the temperature of the solution by the temperature of the water. Molar mass by freezing point depression essay 908 words. Chem 10 experiment 14 molar mass of solid full lab. So the freezing temperature of a 1molal aqueous solution of any nonvolatile molecular. Most curriculum is available for download free ofcharge or with primary literature.
For the phenomenon in pure fluids, see supercooling. In this laboratory, we will find the molar mass of an unknown substance that was combined with bht using freezing point depression. Lab 7 determination of the molar mass of an unknown solid. K f is the molal freezing point depression constant whose value depends only on the solvent. Molar mass by freezing point depression introduction when a nonvolatile solute is dissolved in a solvent, the freezing point of the solution is lowered. Molar mass is useful to identifying an unknown substance. Goals we will measure the freezing point depression of lauric acid that takes place with the addition of benzoic acid. Experiment 20 freezing point depression lab manuals for. Lift an ice cube with a piece of string by sprinkling some salt on it.