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Determining the Molar Mass of Butane Using the Ideal Gas Law

Determining the Molar Mass of Butane Using the Ideal Gas Law. What is an Ideal Gas?. An ideal gas obeys the Ideal Gas Law: P V = nRT where

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Determining the Molar Mass of Butane Using the Ideal Gas Law

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  1. Determining the Molar Mass of Butane Using the Ideal Gas Law

  2. What is an Ideal Gas? An ideal gas obeys the Ideal Gas Law: PV = nRTwhere P = pressure (kPa, kilopascals) V = volume (L, liters) n = moles of gas T = temperature (K, Kelvin) R = gas constant = 8.314 L kPa K-1 mol-1

  3. Partial Pressure of Gases

  4. Dalton’s Law of Partial PressuresPT = P1 + P2 + P3 + …The total pressure in a mixture of gases is the sum of the partial pressures of each gas For dry air: Patm = PN2 + PO2 + PAr + Pother 1atm = 0.78 + 0.209 + 0.009 + 0.002 101.3 kpa = 79.0 + 21.2 + .9 + .2

  5. What about Vapor Pressure of Water (PH2O)? Yes, the vapor coming off a liquid has a partial pressure too. This increases with temperature.

  6. Experimental Approach 1. Measure mass of butane (g) 2. Determine moles of butane 3. Calculate molar mass (g/mol)

  7. Measure Mass of Butane Mass of lighter before releasing gas Mass of lighter after releasing gas

  8. Determine Moles of Butane Part A. Measure the volume of butane collected in the graduated cylinder = V

  9. Determine Moles of Butane Part B. Calculate the partial pressure of butane (P) Subtract the partial pressure of water from atmospheric pressure (in kPa)

  10. Determine Moles of Butane Part C. Calculate moles butane using the Ideal Gas Law PV = nRT is rearranged to solve for n: n = PV/RT Plug in values for P, V, R, and T (R is the gas constant 8.314 J K-1 mol-1

  11. Calculate Molar Mass of Butane Molar Mass = mass/mole (g/mol) Therefore, divide mass (g)of butane by n (moles) Also, calculate the molar mass of butane from its chemical formula (C4H10) and compare with your experimental value.

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