QUESTION 3 In the Dumas experiment, you measure the following data: massgas + fl

Question

QUESTION 3 In the Dumas experiment, you measure the following data: massgas + flasks 143.43 16g masscold water + flask 385.75g density of water= 0.9987g/mL mass empty flask = 142.56g Temperature of boiling water when the system is sealed-105.3°C A) Calculate the molar mass of the gas. Te experiment, we weighed the "empty flask" when it was full of air. This is usually a minor error in an experiment, because we don't remove the air after an experiment, so the effect in other experiments is negligible. However, since we removed all of the air in the flask and replaced it with our gaseous unknown, it has a large effect on the molar mass calculations. Correct for the air in the "empty flask" measurement as follows: B) Use the density of air at room temperature (1.225g/L) to determine the mass of air contained in the flask. C) Subtract the mass of air from your original "empty flask" mass. D) Compute the molar mass of the gas using the real mass of the empty flask. Attach File Browse My Computer

Explanation / Answer

Dumas method is used to determine the molecular weight of unknown substance. Dumas method is used to determine the molecular weight of volatile organic substances that are liquid at room temperature.

Dumas method follow the ideal gas equation to determine the molecular weight.

PV = nRT

For molecular gas

M = mRT/PV

Now mass of gas = 143.4316 g - 142.56 g = 0.8716 g

R = 0.08206 L atm/ mol/K

T = 105.3 C + 273 = 378.3 K

P = 1.008 atm

Volume of vapour is equal to volume of flask = mass of water + flask - mass of empty flask = 385.75 g - 142.56 g= 243.19 g

V = m/D = 243.19 / 0.9987 = 243.50 ml or 0.2435 L

M = 0.8716 X 0.08206 X 378.3 / 0.2435 X 1.008

M = 27.057/ 0.245

M = 110.43 g/mol

Mass of air = Volume of flask X Density of air

Mass of air = 1.225 g/L X 0.2435 = 0.2982 g

C) Mass of empty flask - mass of air = 142.56 - 0.2982 = 142.26 g

D) M = mRT/PV

Now mass of gas = 143.4316 g - 142.26 g = 1.1716 g

R = 0.08206 L atm/ mol/K

T = 105.3 C + 273 = 378.3 K

P = 1.008 atm

Volume of vapour is equal to volume of flask = mass of water + flask - mass of empty flask = 385.75 g - 142.26 g= 243.49 g

V = m/D = 243.49 / 0.9987 = 243.80 ml or 0.2438 L

M = 1.1716 X 0.08206 X 378.3 / 0.2438 X 1.008

M = 36.37/ 0.245

M = 148.45 mol

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