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SCCH159/169 Experiment No.2 Determination of Gas Constant Soraya Pornsuwan Department of Chemistry, Faculty of Science, Mahidol University Credit slide: Aj. Suarwee Akavipat 1
The unit of R (in SI unit system) In SI unit system: Pressure = Pascal (Pa) 1 atm = 101,325 Pa Volume = m3 1 L = 10-3 m3 𝑅 = 𝑃𝑉 𝑛𝑇 = (101,325 Pa) x (22.414 x10−3 m3 ) 1 mol x 273.15 K = (1.01325x105 N/m2 ) x (22.414 x10−3 m3 ) 1 mol x 273.15 K = 8.314 𝑁 ⋅ 𝑚 mol ⋅ K = 8.314 𝐽 mol ⋅ K At STP (Standard Temperature and Pressure): R = 0.082 L.atm = 8.314 J mol.K mol.K 2 T = 0°C = 273.15 K P = 1 atm = 101,325 Pa 1 mol = 22.414 L = 22.414 x 10-3 m3 Unit relations: Pa = N•m2 N•m = Joule PV=nRT
Experiment NaNO2 (aq) + HSO3NH2 (aq) → NaHSO4(s) + N2(g) + H2O (l) nT PV R = Sodium nitrite Sulfamic acid Stock: 2.5% w/v 0.3 M Volume: 20 cm3 2.5 cm3 MW: 67 g/mol 97.1 g/mol HSO3NH2 NaNO2 No air in this area Gas Tube beaker Inverted burette filled with water Need to find P, V and n of N2(g) 3 20 mL 2.5 mL
4 PV=nRT (1) (2) (3) (4) Mole of N2 gas = mole of Sulfamic acid HSO3NH2 0.3M, 2.5mL = 7.5x10-4 mole 4 variables Temperature (T) of N2 gas ≈ T of water in the Beaker 𝑃𝑎𝑡𝑚 = 𝑃𝑁2 + 𝑃𝐻2𝑂 + 𝑃ℎ VN2 = Vx + Vy 106 cm3 = 1 m3 x cm3 = x m3 106 Unit conversion: Vx = 25-x cm3 Vy measured using a cylinder
𝑃𝑎𝑡𝑚 = 𝑃𝑁2 + 𝑃𝐻2𝑂 + 𝑃ℎ 5 PV=nRT (1) (2) (3) 𝑃𝑎𝑡𝑚 = atmospheric pressure (1) Read from a barometer. The unit of this reading is Hecto Pascal 1 Hecto Pa = 100 Pa (2) 𝑃𝐻2𝑂 = saturated water vapor pressure Read from the table. !! Units of Pressure 1 atm = 760 mmHg 760 mmHg = 101325 Pa 1 atm = 101,325 Pa (3) 𝑃ℎ = Pressure at height h From experiment !! Pressure in Pa 760 mmHg = 101325 Pa x mmHg = x (101,325) Pa 760 𝑃𝑁2 = 𝑃𝑎𝑡𝑚 − 𝑃𝐻2𝑂 − 𝑃ℎ
6 3. experimental Temperatures • At room temperature Record temperature!! Volume of N2 gas (Vx+Vy) = …… cm3 → m3 Height of water in the burette (h) = …… cm → mmHg → Pa Temperature of water in beaker = ….. °C → Kelvin For each temperatures, record
7 Lab Report
8
9 Calculation of R: PV = nRT R = PV nT Calculate R from data at room temperature: At room temperature: PN2 = …… Pascal VN2 = …… m3 nN2 = ……. mole T = …….. Kelvin R = PV nT Unit of R = Pa.m3/mol.K = J/mol.K
10 Percentage deviation from the true value % deviation = Calculated R – True value True value X 100 True value of R = 8.314 J/mol.K Summary Calculate R from the data obtained from the experiment. Explain how much your %deviation is from the true value.
11 Finally, summarize your results in the lab report.
12 About quiz: - We will start the quiz in the lab room, ~10 mins after the lab brief. - Students don’t need to sit at your bench. - Limit to only 6 people / row. - Quiz will start when everyone is ready. - You have 8 mins to work on the quiz.