Lauryl alcohol is obtained from coconut oil and is used to make detergents. A solution of 5.00 g of lauryl alcohol in 0.100 kg of benzene lowers the freezing point by 1.4 ºC. What is the approximate molar mass of lauryl alcohol if the molal freezing-point-depression constant for benzene is 5.12 ºC/m?
2 Answers
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find the molality
dT = Kf (molality)
1.4 C = (5.12 C/m)(molality)
molality = 0.2734 molal
find the moles in that 0.100 kg of solvent
0.100 kg benzene @ 0.2734 moles lauryl alcohol / kg benzene = 0.02734 moles of lauryl alcohol
find molar mass of lauryl alcohol
5.00 g of lauryl alcohol / 0.02734 moles = 182.88 g/mol
your answer,
rounded to 3 sig figs is
183 g/mol
(however you may be expected to round off to 180 g/mol, since your “1.4 C” had only 2 sig figs showing)
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What is the approximate molar mass of lauryl alcohol?
Lauryl alcohol is obtained from coconut oil and is used to make detergents. A solution of 5.00 g of lauryl alcohol in 0.100 kg of benzene lowers the freezing point by 1.4 ºC. What is the approximate molar mass of lauryl alcohol if the molal freezing-point-depression constant for benzene is 5.12…
