DOCSLIB.ORG

COLLIGATIVE PROPERTIES the Primary Objective of This Experiment

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
COLLIGATIVE PROPERTIES the Primary Objective of This Experiment 1516L Experiment 3 COLLIGATIVE PROPERTIES Objectives The primary objective of this experiment is to determine the molecular weight of an unknown from its freezing point depression in tertiary-butanol, or t-butanol for short. Discussion Colligative properties are useful for determining molecular weights of unknown samples, because they depend only upon the amount of sample dissolved in a known solvent, and not on the identity of the sample. Colligative properties include boiling point elevation, freezing point depression, vapor pressure lowering, and osmotic pressure. In this experiment you will first determine the freezing point of pure t- butanol, which we will use as a solvent, and also the freezing points of two solutions of an unknown mixed with t-butanol. From the resulting change in temperature (T) that you observe, you will be able to calculate the molar mass of the unknown. The equation which relates T to the concentration of the solute in a known solvent is: T = Kf · m (1) where Kf is the freezing point depression constant and m is concentration in molality units. The freezing point depression constant in equation (1) depends only on the solvent. The solvent we will use in this o experiment is t-butanol, for which Kf = 8.37 C/m. Recall that molality has units of moles of solute per kilogram of solvent. The unit of solution concentration that you may be more familiar with is molarity, which is moles of solute per liter of solution. The problem with using molarity in this experiment is that this quantity can change depending upon temperature. For example, as temperature increases the volume of a solution usually increases meaning that the molarity decreases. Since this experiment is based on observed freezing point changes for a pure solvent vs. a solution, we must use a unit of concentration that does not change with temperature. At first glance you may wonder how you will be able to use equation (1) to determine the molar mass of your unknown. This should become clear if we rewrite equation (1) as follows: T = Kfm = Kf · moles solute = Kf · grams solute/molar mass of solute (2) kg of solvent kg of solvent The only unknown in equation (2) is the molar mass of the solute, which you can solve for algebraically. Safety Precautions Be sure to wear lab coats and goggles at all times during this experiment. Use labeled waste containers for your solutions when finished – do not pour anything down the sink! Peter Norris, YSU Procedure You will work in pairs for this exercise. The experiment involves using the MicroLab interface to obtain a total of three freezing points: one for the pure solvent, and one each for each of two unknown solutions (i.e. containing the same unknown in the same solvent, but having different concentrations). Each of the freezing points will be extracted from a cooling curve, which is a temperature vs. time plot that will be generated in real time during the experiment. The difference in freezing temperatures between the unknown solution and pure solvent is T in equation (1). Thermocouple Calibration Acquire a thermocouple from your instructor and then follow the instructions given in the Thermocouple Calibration document to calibrate the thermocouple using boiling water and then ice-water. Once you are back to the window below you are ready to collect data in the solubility experiment. You should have Thermocouple and Time 1 under the Sensor list; Thermocouple and Time 1 on the Y and X axes of the graph respectively, and also atop Columns A and B on the data table. Sample Preparation 1. Obtain a large (200 mm) test tube and make sure it is very clean and dry. Use soap and water to clean it and then heat the tube carefully over a flame to make sure it is dry. Any water or other impurities that become mixed with your solvent will induce their own colligative effects and result in large experimental errors. 2. Place your test tube in a dry beaker and weigh the beaker plus the test tube. Record the mass on the report sheet. 3. Put about 10 mL of t-butanol in the test tube and weigh the beaker (the same one as before!) plus test tube plus solvent. Record this value on your report sheet. Peter Norris, YSU 4. Prepare a warm water bath by heating about 100 mL of tap water in a 250 mL beaker with a Bunsun burner. The water should not boil; it only needs to get to about 50 °C, which you can measure with the thermometer provided. 5. Prepare a second water bath at room temperature by adding about 200 mL of tap water to a 400 mL beaker. This will be used to initiate the cooling process. Get some ice from the supply table in order to be ready to cool the sample further. Data Acquisition and Analysis 1. Put a two-hole rubber stopper fitted with the calibrated thermocouple and stirring wire into your test tube. Warm the test tube to about 45-50 °C by clamping it in the warm (not boiling!) water bath. Once all of the material in the tube has completely melted, lower the test tube into the room temperature water bath (Figure 1) and clamp it securely. Then place the thermometer in the water bath. Make sure that the level of the water bath is higher than that of the liquid in the test tube. 2. Begin the data acquisition by clicking on the “Start” button on the computer screen. The temperature will decrease gradually and be graphed on the screen. Once the thermocouple temperature (on the computer screen) reaches about 30 °C, add a few chunks of ice to the water bath and stir the ice-water carefully with your glass stirring rod. 3. Once the thermometer shows the ice-water temperature to be about 20 °C, add more ice and stir the ice-water carefully with your glass stirring rod. As the bath temperature approaches 10 °C you should see solid beginning to form in the test tube. The graph on the computer screen should begin to level off as the solid freezes. Continue cooling for several more minutes until the graph temperature starts to decrease again and most of the material in the test tube has frozen. At this point halt the data acquisition by clicking on the “Stop” button. Your graph should look roughly like the one below but the numbers will probably be different. Peter Norris, YSU 4. Click the “Analysis” button, and then “Add curve fit.” Click on the “Time” box and then enter the time limits that define the beginning of the straight portion of the initial cooling slope (see above picture) and the point where the slope begins to level off; then choose “First order” and press “OK.”. Label the analysis “Freezing 1,” then hit “OK.” You should see a line fitted to that part of the cooling curve. 5. Click the “Analysis” button again, then “Add curve fit.” Click on the “Time” box and then enter the time limits that define the beginning of the horizontal portion of the cooling curve (see above picture) and the point where the slope begins to level off again; then choose “First order” and press “OK.” Label the analysis “Freezing 2,” then hit “OK.” You should see a line fitted to that part of the cooling curve. 6. Hover the cursor over the point at which the two lines intersect and you should see a box appear with “X = …, Y = …” Record these values; you will be using the Y value as the freezing temperature of t-butanol in order to calculate T in equation (2). 7. The rest of the experiment is carried out as described in the 1516L manual, i.e. parts 4-7 of the Data Acquisition and Analysis section of the Colligative Properties exercise. Peter Norris, YSU .
Load more

Recommended publications
  • Pre Lab: Freezing Point Experiment 1) Define: Colligative Properties. 2
    Pre Lab: Freezing Point Experiment 1) Define: Colligative properties. 2) List four Colligative properties. 3) Define: Molal freezing point depression constant, Kf. 4) Does the value of Kf depend on the nature of ( solvent, or solute)?_________ 5) a) Show a freezing point of 6.00 °C on a cooling curve for a pure solvent. temperature time b) If the freezing point of a pure solvent is 6.00 °C, will the solvent which is contaminated with a soluble material have a freezing point (higher than, lower than, or same as) 6.00 °C ? Answer: _________. Explain:_______________________________________________________ c) Show a freezing point on the cooling curve for the above contaminated solvent. temperature time 6) Assume you had used a well calibrated thermometer to measure the freezing point of a solvent, can you tell from the cooling curve if the solvent is contaminated with soluble material?______ How can you tell? a) ____________________ b) _____________________ (Next page) 7) Show the freezing point on a cooling curve for a solvent contaminated with insoluble material. temperature time 8) What is the relationship between ∆T and molar mass of solute? The larger the value of ∆T, the (larger, or smaller) the molar mass of the solute? 9) If some insoluble material contaminated your solution after it had been prepared, how would this effect the measured ∆Tf and the calculated molar mass of solute? Explain: _______________________________________________________ 10) If some soluble material contaminated your solution after it had been prepared, how
    [Show full text]
  • Lab Colligative Properties Data Sheet Answers
    Lab Colligative Properties Data Sheet Answers outspanning:Rem remains hedogging: praising she his disclosed reunionists her tirelessly agrimony and semaphore dustily. Sober too purely? Wiatt demonetising Rhombohedral lissomly. Warren The answers coming up in both involve transformations of salt component of moles of salt flux is where appropriate. Experiment 4 Molar Mass by Freezing Point Depression. The colligative property and answer the colligative properties? Constant is what property set the solvent not the solute. Laboratory Manual An Atoms First Approach illuminate the various Chemistry Laboratory. Wipe the colligative property of solute concentration of in touch the following sensors and answer to its properties multiple choice worksheet. Experiment 2 Graphical Representation of Data and the Use all Excel. Investigation of local church alongside lab partners from one middle or high underneath The engaging. For dilute solutions under ideal conditions A new equal to 1 and. Colligative Properties Study Guide Answers Colligative properties study guide answers. Students will characterize the properties that describe solutions and the saliva of acids and. Do colligative properties lab data sheets, see this conclusion of how they answer. Weber State University. Adding a lab. Stir well in data sheet of colligative effects. Strong electrolytes are a colligative properties of data sheet provided to. If no ally is such a referred solutions lab 33 freezing point answers book that. Chemistry Colligative Properties Answer Key AdvisorNews. Which a property. B Answering about 5-6 questions on eLearning for in particular lab You please be. Colligative Properties Chp14 13 13-Freezing Points of Solutions - leave a copy of store Data company with the TA BEFORE leaving lab 1124 No labs 121.
    [Show full text]
  • Chapter 9: Raoult's Law, Colligative Properties, Osmosis
    Winter 2013 Chem 254: Introductory Thermodynamics Chapter 9: Raoult’s Law, Colligative Properties, Osmosis ............................................................ 95 Ideal Solutions ........................................................................................................................... 95 Raoult’s Law .............................................................................................................................. 95 Colligative Properties ................................................................................................................ 97 Osmosis ..................................................................................................................................... 98 Final Review ................................................................................................................................ 101 Chapter 9: Raoult’s Law, Colligative Properties, Osmosis Ideal Solutions Ideal solutions include: - Very dilute solutions (no electrolyte/ions) - Mixtures of similar compounds (benzene + toluene) * Pure substance: Vapour Pressure P at particular T For a mixture in liquid phase * Pi x i P i Raoult’s Law, where xi is the mole fraction in the liquid phase This gives the partial vapour pressure by a volatile substance in a mixture In contrast to mole fraction in the gas phase yi Pi y i P total This gives the partial pressure of the gas xi , yi can have different values. Raoult’s Law Rationalization of Raoult’s Law Pure substance: Rvap AK evap where Rvap = rate of vaporization,
    [Show full text]
  • Δtb = M × Kb, Δtf = M × Kf
    8.1HW Colligative Properties.doc Colligative Properties of Solvents Use the Equations given in your notes to solve the Colligative Property Questions. ΔTb = m × Kb, ΔTf = m × Kf Freezing Boiling K K Solvent Formula Point f b Point (°C) (°C/m) (°C/m) (°C) Water H2O 0.000 100.000 1.858 0.521 Acetic acid HC2H3O2 16.60 118.5 3.59 3.08 Benzene C6H6 5.455 80.2 5.065 2.61 Camphor C10H16O 179.5 ... 40 ... Carbon disulfide CS2 ... 46.3 ... 2.40 Cyclohexane C6H12 6.55 80.74 20.0 2.79 Ethanol C2H5OH ... 78.3 ... 1.07 1. Which solvent’s freezing point is depressed the most by the addition of a solute? This is determined by the Freezing Point Depression constant, Kf. The substance with the highest value for Kf will be affected the most. This would be Camphor with a constant of 40. 2. Which solvent’s freezing point is depressed the least by the addition of a solute? By the same logic as above, the substance with the lowest value for Kf will be affected the least. This is water. Certainly the case could be made that Carbon disulfide and Ethanol are affected the least as they do not have a constant. 3. Which solvent’s boiling point is elevated the least by the addition of a solute? Water 4. Which solvent’s boiling point is elevated the most by the addition of a solute? Acetic Acid 5. How does Kf relate to Kb? Kf > Kb (fill in the blank) The freezing point constant is always greater.
    [Show full text]
  • 16.4 Calculations Involving Colligative Properties 16.4
    chem_TE_ch16.fm Page 491 Tuesday, April 18, 2006 11:27 AM 16.4 Calculations Involving Colligative Properties 16.4 1 FOCUS Connecting to Your World Cooking instructions for a wide Guide for Reading variety of foods, from dried pasta to packaged beans to frozen fruits to Objectives fresh vegetables, often call for the addition of a small amount of salt to the Key Concepts • What are two ways of 16.4.1 Solve problems related to the cooking water. Most people like the flavor of expressing the concentration food cooked with salt. But adding salt can of a solution? molality and mole fraction of a have another effect on the cooking pro- • How are freezing-point solution cess. Recall that dissolved salt elevates depression and boiling-point elevation related to molality? 16.4.2 Describe how freezing-point the boiling point of water. Suppose you Vocabulary depression and boiling-point added a teaspoon of salt to two liters of molality (m) elevation are related to water. A teaspoon of salt has a mass of mole fraction molality. about 20 g. Would the resulting boiling molal freezing-point depression K point increase be enough to shorten constant ( f) the time required for cooking? In this molal boiling-point elevation Guide to Reading constant (K ) section, you will learn how to calculate the b amount the boiling point of the cooking Reading Strategy Build Vocabulary L2 water would rise. Before you read, make a list of the vocabulary terms above. As you Graphic Organizers Use a chart to read, write the symbols or formu- las that apply to each term and organize the definitions and the math- Molality and Mole Fraction describe the symbols or formulas ematical formulas associated with each using words.
    [Show full text]
  • Colligative Properties of Solutions
    V.N.V.N. KarazinKarazin KharkivKharkiv NationalNational UniversityUniversity MedicalMedical ChemistryChemistry ModuleModule 1.1. LectureLecture 55 ColligativeColligative propertiesproperties ofof solutionssolutions NatalyaNatalya VODOLAZKAYAVODOLAZKAYA [email protected] 11 FebruaryFebruary 20212021 Department of Physical Chemistry LLectureecture topicstopics √ Colligative properties of solutions √ Vapor pressure lowering √ Boiling-point elevation √ Freezing-point depression √ Osmosis √ Colligative properties of electrolyte solutions 2 ColligativeColligative propertiesproperties ofof solutionssolutions Colligative properties of solutions are several important properties that depend on the number of solute particles (atoms, ions or molecules) in solution and not on the nature of the solute particles. It is important to keep in mind that we are talking about relatively dilute solutions, that is, solutions whose concentrations are less 0.1 mol/L. The term “colligative properties” denotes “properties that depend on the collection”. The colligative properties are: ¾ vapor pressure lowering, ¾ boiling-point elevation, ¾ freezing-point depression, ¾ osmotic pressure. 3 ColligativeColligative propertiesproperties ofof solutions:solutions: VaporVapor pressurepressure loweringlowering If a solute is nonvolatile, vapor pressure of the solution is always less than that of the pure solvent and depends on the concentration of the solute. The relationship between solution vapor pressure and solvent vapor pressure is known as Raoult’s law. This law states that the vapor pressure of a solvent over a solution (p1) equals the product of vapor pressure of the pure solvent (p1°) and the mole fraction of the solvent in the solution (x1): p1 = x1p1°. 4 ColligativeColligative propertiesproperties ofof solutions:solutions: VaporVapor pressurepressure loweringlowering In a solution containing only one solute, than x1 = 1 – x2, where x2 is the mole fraction of the solute. Equation of the Raoult’s law can therefore be rewritten as (p1° – p1)/p1° = x2.
    [Show full text]
  • COLLIGATIVE PROPERTIES Dr
    SOLUTIONS-3 COLLIGATIVE PROPERTIES Dr. Sapna Gupta SOLUTIONS: COLLIGATIVE PROPERTIES • Properties of solutions are not the same as pure solvents. • Number of solute particles will change vapor pressure (boiling pts) and freezing point. • There are two kinds of solute: volatile and non volatile solutes – both behave differently. • Raoult’s Law: gives the quantitative expressions on vapor pressure: • VP will be lowered if solute is non-volatile: P is new VP, P0 is original VP and X is mol fraction of solute. 0 P1 1P1 • VP will the sum of VP solute and solvent if solute is volatile: XA and XB are mol fractions of both components. 0 0 PT APA BPB Dr. Sapna Gupta/Solutions - Colligative Properties 2 EXAMPLE: VAPOR PRESSURE Calculate the vapor pressure of a solution made by dissolving 115 g of urea, a nonvolatile solute, [(NH2)2CO; molar mass = 60.06 g/mol] in 485 g of water at 25°C. (At 25°C, PH2O = 23.8 mmHg) P P 0 H2O H2O H2O mol mol 485 gx 26.91 mol H2O 18.02 g mol mol 115 g x 1.915 mol urea 60.06 g 26.91 mol 0.9336 H2O 26.91 mol1.915 mol P 0.9392 x 23.8 mmHg 22.2 mmHg H2O Dr. Sapna Gupta/Solutions - Colligative Properties 3 BOILING POINT ELEVATION • Boiling point of solvent will be raised if a non volatile solute is dissolved in it. • Bpt. Elevation will be directly proportional to molal concentration. Tb Kbm • Kb is molal boiling point elevation constant. Dr. Sapna Gupta/Solutions - Colligative Properties 4 FREEZING POINT DEPRESSION • The freezing point of a solvent will decrease when a solute is dissolved in it.
    [Show full text]
  • Colligative Properties: Freezing Point Depression, Vapor Pressure Lowering,Boiling Point Elevation Additional Problems
    Colligative Properties: Freezing Point Depression, Vapor Pressure Lowering,Boiling Point Elevation Additional Problems 1. Adding a nonvolatile ionic solute to water has what effect on the boiling point of the solvent? Does not affect the b.p. Lower the b.p. Raises the b.p. Cannot tell without more information, such as concentration 2. What is the van't Hoff factor? Used in calculations involving the colligative properties. It represents the quantity (in moles) of particles (ions or molecules) in solution per mole of solute dissolved. 3. What is a colligative property (a definition; not "it's freezing point depression", etc.) A colligative property is one which depends upon the number of particles in solution without regard to their identity. 4. Give an example of a colligative property other than freezing point depression. Vapor pressure lowering Boiling point elevation Osmotic pressure 5. What is the equation that relates the freezing point depression and concentration? Define each variable. ∆Tfp = -iKfc ∆Tfp is the freezing point depression, i is the van’t Hoff factor, Kf is the molal freezing point depression constant, and c is the molal concentration of the solute 6. Calculate the molal concentration of a sucrose (C12H22O11) solution that is prepared by dissolving 10.0 g of the solid in 150.0 g of water. -1 C12H22O11, 342.30 g mol n =10.0 g sucrose 342.30 g mol-1 = 0.02921 mol 0.02921 mol cm==0.195 0.1500 kg 7. What is the freezing point of the solution prepared in question 6? The molal freezing point depression constant for water is 1.86 °C/m.
    [Show full text]
  • Colligative Properties: Freezing Point Determination
    At-Home Colligative Properties: Chemistry Experiment Freezing Point Determination Objectives Colligative properties of solutions depend on the quantity of solute dissolved in the solvent rather than the identity of the solute. The phenomenon of freezing point lowering will be examined quantitatively as an example of a colligative property in this at-home experiment. Introduction When a solute is dissolved in a solvent, the properties of the solvent are changed by the presence of the solute. The magnitude of the change generally is proportional to the amount of solute added. Some properties of the solvent are changed only by the number of solute particles present, without regard to the particular chemical nature of the solute. Such properties are called colligative properties of the solution. Colligative properties include the changes in vapour pressure, boiling point, freezing point and the phenomenon of osmotic pressure. If a non-volatile solute is added to a volatile solvent (such as water), the amount of solvent molecules that can escape from the surface of the liquid at a given temperature is lowered compared to the situation where only pure solvent is present. The vapour pressure above such a solution will thus be lower than the vapour pressure above a sample of the pure solvent under the same conditions. Molecules of the non-volatile solute physically block the surface of the solvent, thereby preventing as many molecules from evaporating. This results in an increase in the boiling temperature of the solution as well as a decrease in the freezing point. In this at-home experiment, the freezing points will be measured for: 1.
    [Show full text]
  • Chapter 9 Ideal and Real Solutions
    2/26/2016 CHAPTER 9 IDEAL AND REAL SOLUTIONS • Raoult’s law: ideal solution • Henry’s law: real solution • Activity: correlation with chemical potential and chemical equilibrium Ideal Solution • Raoult’s law: The partial pressure (Pi) of each component in a solution is directly proportional to the vapor pressure of the corresponding pure substance (Pi*) and that the proportionality constant is the mole fraction (xi) of the component in the liquid • Ideal solution • any liquid that obeys Raoult’s law • In a binary liquid, A-A, A-B, and B-B interactions are equally strong 1 2/26/2016 Chemical Potential of a Component in the Gas and Solution Phases • If the liquid and vapor phases of a solution are in equilibrium • For a pure liquid, Ideal Solution • ∆ ∑ Similar to ideal gas mixing • ∆ ∑ 2 2/26/2016 Example 9.2 • An ideal solution is made from 5 mole of benzene and 3.25 mole of toluene. (a) Calculate Gmixing and Smixing at 298 K and 1 bar. (b) Is mixing a spontaneous process? ∆ ∆ Ideal Solution Model for Binary Solutions • Both components obey Rault’s law • Mole fractions in the vapor phase (yi) Benzene + DCE 3 2/26/2016 Ideal Solution Mole fraction in the vapor phase Variation of Total Pressure with x and y 4 2/26/2016 Average Composition (z) • , , , , ,, • In the liquid phase, • In the vapor phase, za x b yb x c yc Phase Rule • In a binary solution, F = C – p + 2 = 4 – p, as C = 2 5 2/26/2016 Example 9.3 • An ideal solution of 5 mole of benzene and 3.25 mole of toluene is placed in a piston and cylinder assembly.
    [Show full text]
  • Solutions and Colligative Properties
    Solutions and Colligative Properties Solution is a homogeneous mixture of two or more substances in same or different physical phases. The substances forming the solution are called components of the solution. On the basisof number of components a solution of two components is called binary solution. Solute and Solvent In a binary solution, solvent is the component which is present in large quantity while the other component is known as solute.[if water is used as a solvent, the solution is called aqueous solution and if not, the solution iscalled non-aqueous solution.] Depending upon the amount of solute dissolved in a solvent we have the following types of solutions: Unsaturated solution A solution in which more solute can be dissolved without raising temperature is called an unsaturated solution. Saturated solution A solution in which no solute can be dissolved further at a given temperature is called a saturated solution. Supersaturated solution A solution which contains more solute than that would be necessary to saturate it at a given temperature is called a supersaturated solution. Solubility The maximum amount of a solute that can be dissolved in a given amount of solvent (generally100 g) at a given temperature is termed as its solubility at that temperature. The solubility of a solute in a liquid depends upon the following factors: (i) Nature of the solute (ii) Nature of the solvent (iii) Temperature of the solution (iv) Pressure (in case of gases) Henry’s Law The most commonly used form of Henry’s law states “the partial pressure (P) of the gas in vapour phase is proportional to the mole fraction (x) of the gas in the solution” and is expressed as p = KH .x Greater the value of KH, higher the solubility of the gas.
    [Show full text]
  • 13.02 Colligative Properties Changes in Solvent Properties Due to Impurities
    13.02 Colligative Properties Changes in solvent properties due to impurities Colloidal suspensions or dispersions scatter light, a phenomenon known as the Tyndall effect. (a) Dust in the air scatters the light coming through the trees in a forest along the coast. (b) A narrow beam of light from a laser is passed through an NaCl solution (left) and then a colloidal mixture of gelatin and water (right) Dr. Fred Omega Garces Chemistry 152 Miramar College 1 1302 Colligative Properties 05.2015 Phase Diagram (Revisited) Heating Cooling Curve and its relation to the Phase Diagram 2 1302 Colligative Properties 05.2015 Colligative Properties It is known that: Dissolved solute in pure liquid will change the physical property of the liquid, i.e., Density, Bpt, Fpt, Vapor Pressure This new developed property is called Colligative Property; a method of counting the number of solute in solution. Vapor Pressure Reduction B. pt. Elevation F. pt. Depression Osmotic Pressure 3 1302 Colligative Properties 05.2015 Evaporation Process Why is responsible for increasing the boiling point of water with the addition of anti-freeze (or salt)? Evaporation occurs when molecules have sufficient energy to escape the interface of a liquid substance. Normal Boiling Point: Temperature at which the vapor pressure of the liquid is equal to the atmospheric pressure. When a solute contaminates the solvent, the surface area is reduced because of the attraction between solute and solvent, thus the physical properties (i.e., vapor pressure) are altered. 4 1302 Colligative Properties 05.2015 A. Vapor Pressure Vapor Pressure Reduction: Solute interferes and prevents solvent molecules from escaping into the atmosphere.
    [Show full text]