Lecture 6 Experiment 4 - Determining % Carbon and Purity - PDF
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This document discusses an experiment designed to determine the % carbon and purity of a sample using chemistry principles. It provides the reaction equation for sodium hydrogen carbonate with sulfuric acid, including calculations using the Ideal Gas Law and Dalton's Law. The experiment involves recording pressure, volume, and temperature data to analyze the evolved gas and calculate the percent composition. The procedure, data, and results are noted.
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Experiment 4 Analysis of Sodium Hydrogen Carbonate by Gas Evolution Ideal Gas Law PV = nRT Reaction Equation: NaHCO3(s) + H2SO4(aq) ➞ H2CO3(aq) + NaHSO4(aq) HCO3— ion is amphoteric When the reaction occurs, CO2 is evolved. Where does CO2 come from? H2CO3(aq) decomposes The equation for the r...
Experiment 4 Analysis of Sodium Hydrogen Carbonate by Gas Evolution Ideal Gas Law PV = nRT Reaction Equation: NaHCO3(s) + H2SO4(aq) ➞ H2CO3(aq) + NaHSO4(aq) HCO3— ion is amphoteric When the reaction occurs, CO2 is evolved. Where does CO2 come from? H2CO3(aq) decomposes The equation for the reaction observed is: NaHCO3(s) + H2SO4(aq) ➞ H2O(l) + CO2(g) + NaHSO4(aq) Determining % Carbon Use Ideal Gas Law to find moles CO2 (n) PV = nRT Use Dalton’s Law to find Pressure of CO2 (P) Ptotal = PCO + PH O 2 2 P CO = Atm P – Water VP 2 Temperature (T) of CO2 = Room Temp TCO = Water Bath Temp 2 Volume (V) of CO2 V CO2 = Volume of water NaHCO3(s) + H2SO4(aq) ➞ displaced by the gas H2O(l) + CO2(g) + NaHSO4(aq) in the Mohr buret Determining %C NaHCO3(s) + H2SO4(aq) ➞ H2O(l) + CO2(g) + NaHSO4(aq) Calculating %C: ▫ First: Definition of %C ▫ Second: Use your data!! ▫ Recall: Mole ratios between reactants and products are all 1:1 ▫ Realize: All C in the NaHCO3 is converted to CO2 1 mol CO2 = 1 mol C 1 mol C = 12.01 g C ▫ Work backwards: g C in %C calculation comes from mol C mol C comes from mol CO2 mol CO2 comes from Ideal Gas Law Determining %Purity NaHCO3(s) + H2SO4(aq) ➞ H2O(l) + CO2(g) + NaHSO4(aq) Remember: %C in a pure sample is always the same ▫ Remember: theoretical Yours isn’t pure! Don’t report a perfect answer! For pure NaHCO3: %Na + %H + %C + %O = 100% actual %C = [g C/g NaHCO3] x 100% for 1 mole of NaHCO3 actual theoretical What should be in your lab notebook? Statement of Purpose – complete sentences at least one of which should include “Ideal Gas Law” Procedure – should refer to the diagram of the apparatus in the lab manual OR draw it yourself! Observations ▫ Appearance of sample initially – dry, white? ▫ What color was the desiccant from last week – blue, pink , purple? What mass of H2O was lost? ▫ Gas evolved – slowly, vigorously? What happened to the water level in the buret? ▫ Did a larger volume of gas evolve from the bigger sample? What should be in your lab notebook? Data recorded ▫ Pressure (+ 0.1 mm Hg) ▫ Volume (+ 0.1 mL) Sample 1 Sample 2 Sample 3 Final volume -Initial volume Vol gas evolved ▫ Temperature (+ 0.1 °C) What should be in your report? Fill in the Report Sheet ▫ Show calculations with formulas and unit labels ▫ Pay attention to Significant Figures Conclusion (3rd person; past tense; passive voice) ▫ Brief overview of procedure with reaction equation ▫ Results explicitly stated % C (expect 10-13 %C) % Purity (expected ?) ▫ Explanation of Results Compare experimental %C with theoretical %C why isn’t the sample 100% pure? How precise were your results? (standard deviation) Extra questions for Experiment 4 in files Next Week Experiment 5: - has prelab questions, - has extra questions, - and you need to prepare your own data tables (see page vi)
