# The Universal Gas Constant and Stoichiometric Calculations

Experiment A4: The Universal Gas Constant and Stoichiometric CalculationsBy: Muna Meerwali #305096211/07/12PurposeTo apply the ideal gas equation and the use of stoichiometric calculations todetermine the value of the ideal gas constant R for a reaction of a known amount of sulfamic acidwith an excess of sodium nitrate (Equation 1). Minor objectives include carrying out a chemicalreaction in a quantitative manner learning how to collect a sample of gas “over water” and theuse and application of the concept of limiting reagents and Dalton’s Law of Partial Pressures.Equation 1: HSO3NH2(aq) NaNO2(aq)Sulfamic acid Sodium nitriteN2(g) H2O(l) NaHSO4(aq)Nitrogen Water Sodiumgashydrogen sulfateIntroduction In this experiment a pressure volume apparatus is used to determine the ideal gasconstant R for the reaction of a known amount of sulfamic acid with an excess of sodium nitrateto produce a quantitative yield of nitrogen gas. When sulfamic acid is the limiting reagent theamount of nitrogen produced is equal to the amount of sulfamic acid used. Therefore applyingstoichiometric calculations the quantitative yield of nitrogen can be used to determine the valueof all the variables in the reaction. By calculating the partial pressure of the nitrogen gasproduced(Equation 1) measuring the temperature and air pressure at which the reactionoccurred the idea gas constant R can be calculated(Equation 2).Equation 1: P(Tot) = P(N2) P(H2O) P(Col)Where P(Tot) is the atmospheric pressure (kPa) P(N2) is the pressure of nitrogen (kPa) P(H2O)is the partial pressure of water (kPa) and P(Col) is the pressure due to the column of water in theburette (kPa).Equation 2: PV = nRTWhere P is the partial pressure of nitrogen gas in the burette (kPa) V is the volume of gas in theburette (L) n is the number of moles of nitrogen gas in the burette (mol) and T is the absolutetemperature (K).Procedureref: Experiment A4 of the Chemistry 217 Home Lab Manual pp. 130-132.Not e: the burette used was in fact a pipette with the tip cut off and could contain a volumegreater than 10mL it is referred to as the 10mL burette for simplicityPart A. Appartus Setup for Determination of the Universal Gas Constant1. A volume of 100mL of water was added to a clean dry 150mL beaker and placed on a retortstand.2. A clean dry 10mL burette was connected to a tube attached to a syringe fitted with a glassbead. 3. A bent straw U tube was loosely fitted into the bottom of the 10mL burette and placed into the150mL beaker submerged in the 100mL of water.4. The apparatus was secured by clamping the burette to the retort stand using two clothespinsattached with a rubber band.5. A volume of 10mL was suctioned into the burette. A small volume of air remained at the topof the burette.Part B. Reagent Setup for Determination of the Universal Gas Constant1. The mass of HSO3NH2 plus vial weighed on a general pan balance was 5.59g.2. The contents of the vial were transferred to a clean dry 100mL volumetric flask.3. The mass of the empty vial weighed on a general pan balance was 5.49g delivering 0.1g ofHSO3NH2 to the 100mL vol. flask.4. Water was used to dissolve the HSO3NH2 in the 100mL vol. flask and added until the level ofwater reached the graduation mark then sealed mixed well and labeled (=standard solution ofsulfamic acid).5. A clean dry 10mL vol. pipette was used to transfer a 10mL aliquot of the sulfamic acidsolution to a clean dry 125mL Erlenmeyer flask.6. A mass of 0.22g of NaNO2 was calculated to be necessary to react with all of the HSO3NH2used to prepare the standard solution of sulfamic acid.7. The mass of NaNO2 plus vial weighed on a general pan balance was 9.16g.8. A spatula was used to transfer NaNO2 to a clean dry glass vial until the mass of the ‘empty’vial weighed on general pan balance was 8.94g delivering 0.22g of NaNO2.9. The contents of the vial were transferred to a clean dry 50mL vol. flask. The vial was rinsedwith a small amount of water and these washings were added to the 50mL vol. flask.10. Water was added to the 50mL vol. flask until the level of water reached the graduation mark then sealed mixed well and labeled (=sodium nitrate solution).Part C. Gas Formation and Collection for Determination of the Universal Gas Constant1. A clean dry 5mL vol. pipette was used to transfer a 5mL aliquot of sodium nitrate solution to aclean dry glass vial (small enough to fit into the 125mL Erlenmeyer flask). 2. The glass vial containing the 5mL aliquot of the sodium nitrate solution was lowered uprightinto the 125mL Erlenmeyer flask containing the 10mL aliquot of the sulfamic acid solution usingtweezers.3. The rubber stopper on the end of the bent straw U tube was fitted tightly into the 125mLErlenmeyer flask.4. The initial level of water in the 10mL burette was measured at 10mL.5. The 125mL Erlenmeyer flask was swirled causing the glass vial to tip initiating the nitrogenproducing reaction.6. The 125mL Erlenmeyer flask was swirled for ten minutes and the final level of water in the10mL burette was measured at 4.1mL.7. The distance between the top of the water in the burette and the top of the water in the 150mLbeaker was measured to be 5.3cm.8. The temperature was measured to be 27®C using a glass mercury thermometer.9. The contents of the 125mL Erlenmeyer flask including the glass vial were emptied and boththe flask and vial were washed and dried.10. Repeat the experiment two times using the prepared standard solution of sulfamic acid andsodium nitrite solution.11. The atmospheric pressure for the day on which the experiment was performed was obtainedfrom online from

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