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 molecular mass by freezing point depression. As the temperature of the water bath reaches the melting point of thepdb, it will begin to melt. Molar mass by freezing point depression essay 657 words. From the graph i determined the freezing point of t butanol as 23 c. 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 todays experiment, you will explore the changes in freezing point behavior of solutions in which tbutyl alcohol 2methyl2propanol is the solvent. The freezing points of these solutions, which will. Molecular mass by freezing point depression darlene dsouza, nithya mitta, ashwini parchure, avni shah prelab 2. This happens whenever a solute is added to a pure solvent, such as cyclohexane. The freezing point depression is directly related to the number of moles of particles. Determination of molar mass by freezing point depression lab.
Molecular mass by freezing point depression lab quizlet. Freezingpoint depression describes the phenomenon that the freezing point of a liquid solvent is depressed when another compound solute is added. The freezing points of these solutions, which will contain known amounts of pdichlorobenzene dissolved in cyclohexane, will be measured. Find the molar mass of a nonpolar molecular compound if 5.
The measured freezing point change will be used to calculate the molar mass of the unknown solid. Energy is neither created nor destroyed, but only transformed from one form to another. Molar mass by freezing point depression objectives. Determination of molar mass by freezingpoint depression studylib. From the data, the molar mass of the solute can be calculated and used to identify the unknown. Freezing point depression is a colligative property observed in solutions that results from the introduction of solute molecules to a solvent. This means that a solution has a lower freezing point than a pure solvent. 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.
After most of the solid pdb appears to have melted, insert the glass stirrer and. Even though the freezing point of butylated hydroxytoluene is known, it. In this experiment, the freezing point depression of stearic acid after adding an unknown fatty acid was determined. 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 by depression of freezing. In the second part of the lab, the freezing point of a cyclohexane solution will be prepared that contains a known mass of an unknown organic solid. Students determine the molar mass of an unknown fatty acid dissolved in a known fatty acid using freezing point depression and colligative properties. Experiment 3 colligative properties freezingpoint depression and molar mass by, andrew klingsporn joby j. Determine the molar mass from the mass of the unknown and the number of moles of unknown. Molar mass from boiling point elevation or freezing point. This experiment focuses on the property of freezingpoint depression. Molar mass from freezing point depression physics forums.
The molal freezing point depression constant for h2o, kf, is given as 1. Molar mass of a molecular compound by freezingpoint. 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 reproduction of this manual is funded by the tuition grant. Determining molar mass of unknown using freezing point. The molar mass is an important value that must be known in order to identify an unknown substance or to characterize a.
Homework equations change of temperaturefp constantmolality mmmolesgram mmoles of solutekg of solvent. Test tube, 18150 millimeters wire stirrer weighing dish timer, seconds chemicals. Lab report 4 lab report 4 introduction freezingpoint. Lab 7 determination of the molar mass of an unknown solid.
Summary of lab procedure if not already completed, crush a small amount of bht and pack it into a capillary tube. What is the normal meltingfreezing point for tbutyl alcohol. The temperature remains constant as a pure liquid freezes only if the solid and liquid are. The freezing point depression is a colligative property, which. Freezing point depression occurs when a solute is added to a solvent producing a solution. 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. The freezing point depression is based on the molal concentration moles of solute per kg of solvent. In addition, there is a slow gradual fall in temperature as freezing proceeds. Molar mass by freezing point depression ap chemistry. Deliver the liquid to the beaker and find the mass of the beaker and the liquid. When a solution forms, the freezing point of the solution is lower than the freezing point of the pure solvent.
Ap chemistry lab molar mass by freezing point depression prelab questions 1. K f is the molal freezing point depression constant whose value depends only on the solvent. The purpose of this experiment was to determine the molar mass of an unknown, nonvolatile solute. 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. Background there are a number of ways of determining the molar mass of a substance. Determine the change in boiling or freezing point temperature solution and pure solvent. 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. 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. What is the normal melting freezing point for tbutyl alcohol. If the freezing point of the solution had been incorrectly read 0. One of the uses of colligative properties is to determine the molar mass of an unknown substance.
Learn vocabulary, terms, and more with flashcards, games, and other study tools. 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. In this laboratory, we will find the molar mass of an unknown substance that was combined with bht using freezing point depression. The freezing point depression can be determined by subtracting the temperature of the solution by the temperature of the water. 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 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.
Freezing point of a solution of liqud unknown freezing point depression. Determination of molar mass by freezingpoint depression. Freezing point depression and molar mass prepared by edward l. Determination of molar mass by freezing point depr.
Molar mass by freezing point depression lab question. Determination of molar mass by freezingpoint depression when a solute is dissolved in. Chapter 02 question 112 solutions cbse, rbse, up, mp, bihar. Calculating the molar mass of a solute from freezing point. To determine the molar mass of an unknown substance by measuring the freezing point depression of a solution of an unknown substance and bht. Pdf effects of freezing point depression on molecular weight. 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. Determination of molar mass by freezingpoint depression pdf. 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.
Molal freezing point depression constants of several solvents solvent freezing point, c kf, c. That is, increasing the molar or molecular mass will have a smaller effect on the freezing point. Determine the change in freezing point from the observed freezing point of the solution and the freezing point of the pure solvent. Lab 7 determination of the molar mass of an unknown. The type of property that will be explored in this experiment is the colligative property. Temperature is a measure of the average kinetic energy of atoms and molecules. Molar mass by freezing point depression 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 cyclohexane.
Combining freezing point depression and selfdiffusion data for characterizing aggregation. 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. Molar mass by freezing point depression november 28, 2012 name lab partner purpose. The molality, m, of a solution can be expressed in terms of the molar mass of the solute. What is the difference between a solvent and solute. Properties based only on the number of solute particles and not their identity are known as colligative properties. Determining molar mass by freezing point depression background information. 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. 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. 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 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. Conclusion the purpose of this experiment was to determine.
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. Molecular mass by freezing point depression lab by av s on prezi. Please check if delta tf or molality of t butanol solution is correct. When a student finished mixing the solution in the test tube step 8, the fire alarm went off and the building was evacuated for a period of time. Brown, lee university the student will become familiar with properties inherent to solutions and will use them to determine the molar mass of a 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. The size of the k f for a given solvent, which are well known. Now you need to find the moles to complete the problem. Ap chemistry lab molar mass by freezing point depression pre lab questions 1.
Chm112labmolarmass byfreezing pointdepressiongradingrubric criteria pointspossible pointsearned. Molar mass determination by freezing point depression. This lab replaces traditional experiments using hazardous organic solvents. Calculating molar mass from freezing point depression. Freezing point depression the size of the freezing point depression depends on two things. Chm112 lab molar mass by freezing point depression. Continue to heat the water bath gently, allowing the temperature to rise slowly above 60c. The colligative property freezing point depression is evaluated as a. Sucrose is considered a green compound for this lab because it requires no hazardous material disposal and produces no toxic fumes. Molecular weight of a water soluble solid unknown by. Molecular weight of a water soluble solid unknown by freezing. Introduction of differential scanning calorimetry in a general. Molecular mass by freezing point depression lab by av s on.
These include freezing point depression, osmotic pressure, and boiling point elevation. Molar mass by freezing point depression lab essay 602 words. Jan 23, 2012 im trying to determine the molar mass of an unknown substance by using freezing point. Determination of the molar mass of an unknown solid by. Lab 07 determining molar mass by freezing point depression. 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 freezing point depression of water. Molar mass is useful to identifying an unknown substance. What is the formula and molar mass for tbutyl alcohol. I use cetyl alcohol to calculate freezing point depression constant my data from the experiment freezing point of pure bht. You know the freezing point depression of the solution and the cryoscopic constant, so you can calculate the molality. And the molal concentration of the solution which depends on the number of moles of solute and the kg of solvent. Van koppen, general chemistry laboratory manual, recycling aluminum. The given thermometer should be used to record when the freezing points happen. Calculating the molar mass of a molecular substance from its freezing point depression.
Ask your teacher if your unknown compound dissociates, and, if so, how many ions are contained in a single formula unit. Why is freezing point depression used to determine molar mass rather. Jan 19, 2016 determining molar mass of unknown using freezing point depression colligative properties duration. Both the boilingpoint elevation and the freezingpoint depression see chapter 2 are directly. K f is the molal freezing point depression constant whose. In this experiment, you will determine the molar mass of an unknown solute. Chandana meegoda 2112009 purpose the purpose of this experiment is to determine the molar mass of an unknown substance using its freezing point depression. The temperature at which a solution freezes is lower than that for the pure solvent. 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. Combining freezing point depression and selfdiffusion data for. Exercise 1 determination of molar mass from freezing point.
The cooling curves for the solutions were generally accurate, and resulted in a realistic molar mass, which means this lab was a success. Determination of molecular weight by 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. What is molality and how is it different from molarity. 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. 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. Freezingpoint depression to determine an unknown compound.
Determination of molar mass by freezing point depression page 5 of 6 5. Molar mass by freezing point depression continued 2 21 flinn cientiic inc all ights esered 5a1. Determination of 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. The molar mass would be lower because if the freezing point was 0.
Lab 7 determination of the molar mass of an unknown solid by. Start studying molecular mass by freezing point depression lab. Thus, as the molar mass increases, the freezing point depression decreases. Chemistry is the study of the chemical and physical properties of substances. Tare an erlenmeyer flask on the balance and place a clean, dry test tube 20 cm. Youve just watched joves introduction to using freezing point depression to determine the identity of an unknown compound.
Chm 112 molar mass by freezing point depression youtube. What are the measurements that must be taken to find the molar mass of an unknown solid using the freezing point depression method. Determination of molar mass by freezing point depression camphor melts at 179. Calculate and enter the freezing point depression of a solution of 80.
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