1. A student determines the freezing point of a solution of 0.92 g of unknown in...

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1. A student determines the freezing point of a solution of 0.92 g of unknown in 23.78 g of t-butyl alcohol. He obtains the following time and temperature readings (times are in minutes, temperatures are in C): Time (min) 0 Temp (C) Time (min) 5.0 4.5 Temp (C) 20.2 20.1 32.9 C. 0.5 31.3 e. 1.0 27.7 a. Plot these data. You may use the graph paper provided on the next page, or if you prefer, you can plot them on your own paper or provide a print out of a computer plot. Note that the first several points fall roughly on a straight line. The last several points fall on a better straight line. The temperature at which these lines intersect is the freezing point of the solution. Ignore the slight supercooling which was observed. b. What is the freezing point of the solution? f. 1.5 2.0 2.5 3.0 3.5 4.0 25.1 23.2 21.6 20.3 19.4 20.3 What is the freezing point depression, ATf? The freezing point of PURE t-butyl alcohol is 24.5 C. 5.5 6.0 6.5 7.0 7.5 8.0 20.0 19.8 19.7 19.6 19.5 19.3 d. What is the molality (m) of the unknown in the solution? For the solvent t-butyl alcohol, Kf = 8.09 C/m. How many moles of unknown are in the solution? C What is the molar mass of the unknown? m moles g/mole 7 1. A student determines the freezing point of a solution of 0.92 g of unknown in 23.78 g of t-butyl alcohol. He obtains the following time and temperature readings (times are in minutes, temperatures are in C): Time (min) 0 Temp (C) Time (min) 5.0 4.5 Temp (C) 20.2 20.1 32.9 C. 0.5 31.3 e. 1.0 27.7 a. Plot these data. You may use the graph paper provided on the next page, or if you prefer, you can plot them on your own paper or provide a print out of a computer plot. Note that the first several points fall roughly on a straight line. The last several points fall on a better straight line. The temperature at which these lines intersect is the freezing point of the solution. Ignore the slight supercooling which was observed. b. What is the freezing point of the solution? f. 1.5 2.0 2.5 3.0 3.5 4.0 25.1 23.2 21.6 20.3 19.4 20.3 What is the freezing point depression, ATf? The freezing point of PURE t-butyl alcohol is 24.5 C. 5.5 6.0 6.5 7.0 7.5 8.0 20.0 19.8 19.7 19.6 19.5 19.3 d. What is the molality (m) of the unknown in the solution? For the solvent t-butyl alcohol, Kf = 8.09 C/m. How many moles of unknown are in the solution? C What is the molar mass of the unknown? m moles g/mole 7

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