Chemistry 11 Santa Monica College Date:10/23/17 Lab Section: 4017 Name Lucua Aur

Question

Chemistry 11 Santa Monica College Date:10/23/17 Lab Section: 4017 Name Lucua Aurer-vean Determination of Molar Mass via the Dumas Method Prelab A student performs the Dumas bulb experiments and collects the following data: Mass of empty flask Mass of flask filled with water: Temperature of water in flask: Atmospheric pressure: 31.022 g 161.175 g 22.7 C 759.1 mmHg She then performs the experiment with her unknown liquid and records the following data mass oume densirj Temperature of boiling water bath: Mass of condensate after boiling: 100.1°C 0.306 g Use these data to find the molecular mass of her unknown liquid. Show all work below das M T PV Determination of Molar Mass via the Dumas Method Page 1 of

Explanation / Answer

The molar mass of unknown is calculated using the ideal gas equation

PV = nRT

or PV = (mass/molarmass) RT

where P = atmospheric pressure

V = measured volume of the vessel

T = abolute temperature of boiling water bath

R = ideal gas constant

i) volume of the vessel

mass of water that filled the vessel = mass of filled flask - mass of empty flask

= 161.175 - 31.022 g

= 130.153g

Since density of water = 1g/mL

The volume of vessel = 130.153 mL

= 130.153x10-3 L

atmosphereic pressure = 759.1 mm

= 759.1/760atm

temperature = 100.1 C

= 100.1 +273.15 K

= 373.25K

gas constant R = 0.0821L.atm/k.mol

mass of sample = 0.306g

Thus substituting all these values in idela gas equation and calculating molar mass

molar mass = mass x RT/PV

= 0.306g x 0.0821 L.atm/K.mol x 303.25K / (759.1/760atm)(130.153/1000L)

= 58.6 g/mol

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