Hope someone could help me to answer these questions Diethyl ether (CH_3CH_2OCH_

Question

Hope someone could help me to answer these questions Diethyl ether (CH_3CH_2OCH_2CH_3) is very volatile and very flammable. An experiment was performed using a sample of diethyl ether in a flask heated to 40.0 degree C. After cooling, the combined mass of the flask, foil cap, and condensed ether was 95.9808 g. The empty flask and foil massed 95.2456 g and had a volume of 300.0 mL. The atmospheric pressure in the laboratory was 746.5 torr. a) Use the experimental data to calculate the molar mass of diethyl ether.(experimental value) b) Use the molar masses of C, H and O to calculate the molar mass of diethyl ether (accepted value). c) Calculate the percent error of the molar mass determination in the experiment. % error = accepted value - experimental value/accepted value times 100

Explanation / Answer

Question a

Boiling point of diethyl ether is 34.6oC. On heating diethyl ether to 40oC, it vapourises and its gaseous form occupies entire volume of flask and some amount is lost to atmosphere. Mass of gaseous form that is present in flask can be determined using initial and final weights. Number of moles of gaseous diethyl ether in flask can be calculated using ideal gas equation. Using values of mass and number of moles, the molar mass can be calculated.

Temperature, T = 40oC = 273 + 40 = 313 K ;      Volume = 300 mL = 0.3 L   (1000 mL = 1L)

Pressure, P = 746.5 torr = 0.98 atm (760 torr = 1 atm)

Ideal gas equation is, PV = nRT     where, n = number of moles of gas

and R = universal gas constant = 0.082057 L atm K-1mol-1

So number of moles of gaseous diethyl ether in flask is, n = PV / RT = (0.98 * 0.3) / (0.082057 * 313)

n = 11.447 * 10-3 mol

So number of moles of gaseous diethyl ether in flask is, n = 11.447 * 10-3 mol ..................(1)

Mass of diethyl ether + flask + foil cap = w2 = 95.9808 g

Mass of empty flask + foil cap = w1 = 95.2456 g

Mass of diethyl ether, m = w2 - w1 = 95.9808 - 95.2456 = 0.7352 g

So mass of diethyl ether in flask is m = 0.7352 g          .............................(2)

Molar mass = mass / number of moles = 0.7352 / (11.447 * 10-3 )           [using results (1) and (2)]

Hence, molar mass of diethyl ether = 64.2264 g / mol

Molar mass of diethyl ether calculated using experimental data = 64.2264 g / mol

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Question b

Molar mass of carbon, MC = 12.0107 g / mol

Molar mass of hydrogen, MH = 1.0079 g / mol

Molar mass of oxygen, MO = 15.9994 g / mol

Given, diethyl ether is CH3CH2OCH2CH3

So, molecular formula of diethyl ether is C4H10O

So, molar mass of diethyl ether = (MC * 4) + (MH * 10) + (MO * 1)

= (12.0107 * 4) + (1.0079 * 10) + (15.9994 * 1) = 48.0428 + 10.079 + 15.994

= 74.1158 g / mol

Hence, molar mass of diethyl ether (accepted value) = 74.1158 g /mol

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Question c

Given, percent error = [(accepted value - experimental value) / accepted value ] * 100

Here, experimental value = 64.2264 g / mol         (from answer to question a)

accepted value = 74.1158 g / mol                         (from answer to question b)

So, percent error = [ (74.1158 - 64.2264) / 74.1158 ] * 100   = 13.34%

Hence, percent error of the molar mass determination in the experiment is 13.34%

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