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Chemistry 121 Colligative Properties Lab Exhibition of Picked Calculations via Choice We Determination of Kf pertaining to Naphthalene To determine the Kf intended for naphthalene, we need to find the difference in the cold point of pure naphthalene and the remedy of 1, 4-dichlorobenzene in naphthalene. Let’s say that we did this kind of experiment, employed 1 . 00 g one particular, 4-dichlorobenzene in 10.
00 g naphthalene, and found which the freezing temperatures of natural naphthalene was 78. 2C, while those of the solution was 75. 4C. This gives all of us a? Tf of 79. 2C , 75. 4C = 2 . 8C.
Making use of the equation intended for freezing level depression and solving pertaining to Kf, we have,? Tf = Kfmsolute Kf sama dengan? Tf/msolute where msolute equals the molality of the solute. What is the molality with the solute? msolute=molality of solute = skin moles of solute/kg solvent moles of solute = 1 ) 00 g 1, 4-DCB/146. 9 g/mol = 6. 81 back button 10-3 skin moles 1, 4-DCB kg of solvent sama dengan 10. 00 g naphthalene/1000 g/kg = 0. 01 kg solvent msolute = 6. 81 x 10-3 moles one particular, 4-DCB/0. 01 kg naphthalene = zero. 681 meters Kf sama dengan 2 . 8C/0. 681 m = 5. 112 Kkg/mol The actual value for Kf for naphthalene is 7. 45 Kkg/mol, so jooxie is a fair quantity off the draw.
This is a rather crude research, so that’s to be expected. Determination of the Molecular Mass/Molecular Formula of Much needed Sulfur Even though this try things out didn’t move as well as I would have loved, there seemed to be some difficulties with the presentation of the info as they were obtained, therefore i thought I’d demonstrate how to do this calculation. Elemental sulfur contains a molecular formula of S8 (there are eight sulfur atoms in a molecule of sulfur, just like you will find 2 hydrogen atoms in a molecule of hydrogen). So , the purpose of this experiment really was just to observe how close you may come to this answer.
Practice test: answer key
To get the molar mass (and, making use of the atomic mass, the molecular formula) for sulfur, we first need to find the freezing stage of a remedy of sulfur in naphthalene. Let’s say we all made this kind of a solution with 0. 500 g powdered sulfur in 10. 00 g of naphthalene, and found that it’s freezing level was seventy six. 7C. To find the molecular mass, let’s initially find the molality with the solution simply by solving these equation for msolute. (NOTE: Contrary to what many of you thought, weight loss find the molality of the solution just by using the atomic mass of sulfur to find the moles of sulfur, emember that molecular sulfur provides 8 sulfur atoms, but for the functions of your test, you “don’t know this” and are looking for that fact out. So , we’re solving for the molar mass just like the trouble on the most recent exam regarding an unknown solute. )? Tf =Kfmsolute msolute =? Tf/Kf Our? Tf = 78. 2C , 76. 7C = 1 ) 5C. Discussing use the “real” Kf instead of the one we calculated so we’ll have a better answer, msolute = 1 . 5C/7. 45 Kkg/mol = zero. 201 mol/kg (molal) Now, we know the molality, and know the range of kilograms of solvent (0. 010 kg of naphthalene), let’s get the number of skin moles of sulfur present. oles of sulfur = molality x kilogram of solvent = zero. 201 m x zero. 010 kg = 0. 00201 skin moles sulfur Right now, divide the mass of sulfur we took by this range of moles to have the molar mass of sulfur, 0. 500 g sulfur/0. 00201 skin moles sulfur sama dengan 248. almost eight g/mol This is the molar mass of important sulfur, break down it by the atomic mass of sulfur (32. 07 g/mol) to find out how many sulfur atoms there are within a sulfur molecule. We get 7. 76? eight atoms, just isn’t it amazing how you can find the right answer when you make up your personal data? 😉 Back to Basic Chemistry Home-page Back to General Chemistry Syllabus
