need help calculating the moles of vapor Unknown number Mass of dry flask, foil,

Question

need help calculating the moles of vapor Unknown number Mass of dry flask, foil, and rubber band (g) Vaporize the Sample Instructor's approval of apparatus Temperature of boiling water (degree C, K) Mass of dry flask, foil, rubber band, and vapor (g) Determine the Volume and Pressure of the Vapor Volume of 125-mL flask (L) Atmospheric pressure (torr, atm) Calculations Moles of n_vapor, (mol) Mass of m_vapor(g) Molar mass of compound (g/mol) Average molar mass (g/mol) Standard deviation of molar mass Relative standard deviation of molar mass (% RSD) Show the calculation for the standard deviation and the relative standard deviation (as %RSD) of the molar mass of the unknown. Data Analysis, C and D.

Explanation / Answer

D. Calculations

1. For trial 1, moles of vapor = PV/RT

with,

P = 0.9831 atm

V = 0.15 L

R = gas constant

T = 350.55 K

we get,

moles of vapor = 0.9831 atm x 0.15 L/0.08205 L.atm/K.mol x 350.55 K = 5.127 x 10^-3 mols

2. Mass of vapor = 0.264 g

3. Molar mass of vapor = g/moles = 0.264/5.127 x 10^-3 = 51.49 g/mol

Similarly we can do the same for Trial 2 and Trial 3

4. average molar mass = 51.83 + 40.224 + 38.84/3 = 43.52 g/mol

5. Standard deviation : mean = sum of all values/3 = 43.52 g/mol

variance = sum of (mean - Trial 1 value)^2/3 = 63.553 + 10.864 + 21.90/3 = 32.10647

standard deviation = sq.rt.(32.10647) = 5.67

6. Relative standard deviation,

max(43.52 + 5.67) + min(43.52 - 5.67)/2 = 43.52%

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