what is the change in temperature of the freezing point cyclohexane Chem 1A Free
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what is the change in temperature of the freezing point cyclohexane
Chem 1A Freezing Point Depression Advanced Study Assignment Name A student measures the mass of a beaker with an empty test tube in it, and finds that the mass is 156.852 grams. They then add approximately 15 mL of pure cyclohex reweigh the beaker and test tube with cyclohexane in it. The ane to the test tube and beaker, test tube and cyclohexane weighs 171.206 grams. Then they measure the freezing point of the pure cyclohexane that it is 6.60 °C. The student then adds 0.300 grams of an unknown hydrocarbon cyclohexane in the test tube and stirs it until it has dissolved. Finally, the freezing point of the cyclohexane and hydrocarbon solution was measured and found to be 1.25 eC. The freezing point depression constant for cyclohexane is 20.2 C/m to the 1. What is the change in temperature of the freezing point? Imol 841 0105mel o 0003 K T of freezing point: 2. What is the molality of the unknown hydrocarbon in the solution? Molality of hydrocarbon: 3. What is the mass of cyclohexane in the test tube in kilograms? 11.aovSxiong Mass of cyclohexane: 4. How many moles of the unknown hydrocarbon are present in the solution? Moles of hydrocarbon 5. What is the molar mass of the unknown hydrocarbon? Molar Mass of hydrocarbon:Explanation / Answer
1. DT = t0-tS
= 6.6-1.25
= 5.35 C
2. dTf = i*Kf*m
i = vanthoff factor of hydrocarbon = 1
Kf of cyclohexane = 20.2 c/m
m = molality = ?
5.35 = 1*20.2*m
m = 0.265
3. mass of cyclohexane = 171.206-156.852 = 14.354 g
= 0.014354 kg
4. no of mol of hydrocarbon = molality*mass of cyclohexane in kg
= 0.265*0.014354
= 0.0038 mol
5. molarmass of unknown hydrocarbon = w/no of mols
= 0.3/0.0038
= 79 g/mol
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