Calculation of molecular weight from freezing point depression data problem: the freezing point of a solution that contains 100 g of an unknown compound, (a), dissolved in 100 g of benzene is found to be 207 o c. Molecular mass by freezing point depression lab fp1 juniata college science outreach new and improved introductory manual, 2000 introduction once a solution has been formed, the solution displays properties different from those of. This solution contains step-by-step calculations and explanations to determine the molecular weight, boiling point, vapour pressure and the highest to lowest freezing points all workings are shown using equations of freezing point and molarity and a graph of freezing points is included. Molecular weight (mw) is an older term for what is now more correctly called the relative molar mass (m r) this is a dimensionless quantity (ie, a pure number, without units) equal to the molar mass divided by the molar mass constant freezing-point depression the freezing. Molecular mass by freezing point depression prelab purpose graphs conclusion 1 to determine the molecular mass of an unknown substance by finding the freezing point of two solutions (bht and para-dichlorobenzene, and bht and the unknown.
The molecular weight of this unknown compound can be determined by observing the freezing point of a solution of the compound in cyclohexane and comparing it to the freezing point of pure cyclohexane. 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 cyclohexanethe freezing points of these solutions, which will contain known amounts of p-dichlorobenzene dissolved in cyclohexane, will be measured. Experiment #8 molecular weight by freezing point depression maureen shultz november 14, 2015 i purpose the purpose of this experiment was to determine the molecular weight of two unknown substances by measuring the freezing point depression of an aqueous solution of the unknown substances. Computer 4 advanced chemistry with vernier 4 - 1 using freezing-point depression to find molecular weight when a solute is dissolved in a solvent, the freezing temperature is lowered in proportion to the number.
Colligative properties such as freezing point depression or boiling point elevation can be used to calculate the molecular weight of a soluble solid to complete this calculation, the mass of solute and solvent must be known as well as the freezing points/boiling points of the pure solvent and the solution. Colligative properties molecular weight determination by freezing point depression introduction a solution is a homogeneous mixture (has a constant composition throughout) which consists of a dissolved substance, the solute, and a dissolving medium, the solvent. Lab - molecular weight determination by freezing point depression the boiling point of the solution 3 the molecular mass of the solute from the freezing point or the boiling point molecular weight determination by freezing point depression unknown number: _____ 1 volume of glacial acetic acid _____ ml.
Determination of molar mass by freezing point depression page 3 of 6 drawing the straight line in the solid-liquid region of the graph, ig nore points where supercooling is observed. Students will calculate the freezing-point depression as the ∆t between the freezing temperature of pure lauric acid and that of the lauric acid-benzoic acid solution the freezing-point depression constant (k f ) for lauric acid is given (39˚c•kg/mol. The application of freezing point depression is the determination of the molecular weight of the substance x a weighed amount of the solute (substance x) is dissolved in a known mass of solvent (naphthalene.
Determining molar mass we can use a measurement of any one of the following properties to determine the molar mass (molecular weight) of an unknown that is the solute in a solution: boiling point elevation freezing point depression from freezing point depression. The molal freezing point depression constant for h2o, kf , is given as 186 °ckg/mole thus a100 m aqueous solution freezes at -186 °c instead of 000°c which is the normal freezing point of the solution is determined from the graph by drawing two straight lines through the data. 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. Cyclohexanol, c6h11oh, is sometimes used as the solvent in molecular weight determination by freezing point depression if 0253 g of benzoic acid, c6h5cooh, dissolved in 1245 g of cyclohexanol, lowered the freezing point of pure cyclohexanol by 655 0c, what is the molal freezing point constant (kf) of this show more cyclohexanol, c6h11oh, is sometimes used as the solvent in molecular. Example 2 molar mass from freezing point depression the freezing point of a solution that contains 100 g of an unknown compound, dissolved in 100 g of benzene is found to be 207 o c the freezing point of pure benzene is 548 o c.
Better in the sense of determining the molecular mass of the compound from using either the boiling point or the freezing point if you took a solution and divided in 2 on one you determine the freezing point depression and with the other you determine the boiling point elevation. General chemistry i (fc, 09 - 10) lab # 13 – molecular weight determination by freezing point depression revised 8/19/2009 3 to find the intersection of the two lines, solve the two equations, 4 and 5, simultaneously for y. The freezing point of the benzoic acid is higher than the freezing point of the solution of both acids this in turn leads to a smaller calculated freezing point depression this would indicate a smaller molality of benzoic acid than the actual value of the molality of benzoic acid of the solution. A colligative property of a solution, freezing-point depression, is used in this experiment to determine the molecular weight of an unknown compound a the freezing-point of a solution is always lower than the freezing-point of the pure solvent.
In an earlier experiment, you observed the effect on the cooling behavior at the freezing point of adding a solute to a pure substance by measuring the freezing point depression, δ t , and the mass of benzoic acid, you can use the formula above to find the molecular weight of the benzoic acid solute, in g/mol. Determine the molecular weight of unknown compound using freezing point depression use the “lab : how to” link from the class website if you need help with how to use balance, bunsen burner and such. The freezing point of pure benzene is 548 oc the molal freezing point depression constant of benzene is 512 oc /molal what is the molecular weight of the unknown compound.