The objective of the experiment was to verify the molar volume of a gas and gas constant.? The method in which was used to determine the volume of H2 gas at standard temperature and pressure and the gas constant was to measure a strip of magnesium and place it inside the gas buret which contained hydrochloric acid, blue dye and distilled water and allow the reaction to occur. Once the reaction was complete and there were no visible gas bubbles, the volume was obtained and recorded.
This procedure was completed three times.
After gathering all the information needed, and using the ideal gas law to find the gas constant for each trial, the average of the three results were then calculated and turned out to be 0. 0841L atm/k mol. The approximation error turned out to be 0. 00404 L atm/k mol. Finding the molar volume at STP was done by multiplying the number of moles of the gas by the value of the gas constant found in the experiment.
Introduction: The purpose of this experiment is to discover how the molar volume of a gas and the gas constant is found. The molar volume can be found by the equation: MV = V/n = RT/P here it is either dependent on a given volume (V) and a number (n) of moles or a constant temperature (T), pressure (P) and the gas constant. In Avogadro’s Law it is stated that when the pressure and volume are constant the volume is directly proportional to the number of particles (moles).? In the experiment that will be conducted, with the formula Mg(s) +2HCl(aq) > H2(g) + MgCl2(aq) Hydrogen gas is produced when hydrochloric acid and magnesium are mixed. The volume of hydrogen gas is found by measuring the volume of the buret after the reaction occurred.
The number of moles is found by converting the given amount of grams of magnesium into moles of magnesium using the molar mass and then using the equation to find the number of hydrogen gas mole with a one to one mole ratio. Once finding these two important figures the gas constant can be obtained using the Ideal Gas Law equation: PV=nRT Finally the molar volume is found by dividing the volume of hydrogen gas at STP by the number of moles of hydrogen gas obtained in the experiment and multiplying by one mole of hydrogen gas. Materials and Equipment: One 50mL gas buret ?Piece of magnesium ribbon (approximately 0. 04) ?One copper wire ?1 600mL Beaker ?Tap water ?Blue dye ?10mL 6 M HCL (for each trial) ?Distilled water ?Wash bottle ?1 Buret Stopper ?1 buret stand ?1 plastic tray ?Analytical balance ?1 10mL Graduated Cylinder ?Soap Safety: oHydrochloric acid—keep this away from eyes or any exposed skin oBlue dye –will dye your skin—just wash skin thoroughly Procedure: ?The buret stand was set up and the gas buret was placed inside the clamp. The wash bottle was filled with distilled water and set aside for later use.
Also the 600mL beaker was filled with tap water to the 500mL mark and placed on the stand. One 50mL gas buret was checked out from the lab technician. ?Using the plastic tray, the magnesium ribbon was weighed and the mass was recorded. ?The copper wire was wrapped around the magnesium ribbon until the magnesium was sufficiently covered. With the other end of the copper wire, the wire was then fished into the center of the stopper and bent at the other end. ?Placing the wire, magnesium and stopper off to the side, the gas buret was then prepared. Ten drops of the blue dye was placed inside the gas buret.
The gas buret was placed back onto the buret stand and 10mL of Hydrochloric acid was measured out using the 10mL graduated cylinder. The Hydrochloric acid was then carefully poured into the gas buret. ?Using the distilled water in the wash bottle, the gas buret was filled with distilled water until it reached the top of the buret. Once the distilled water reached the top, the stopper with the copper and magnesium ribbon was positioned at the top of the buret. A few drops were placed inside the whole of the stopper as to guarantee that the buret was completely filled with distilled water. Placing a finger on the whole to prevent any water to spill, the buret was carefully turned upside down so that the stopper with the finger still covering the whole was on the bottom. The stopper of the buret was then placed inside the 600mL beaker that contained the tap water, the finger released the whole from the stopper once it was underwater and the buret was secured on the stand. The reaction then began. ? Once the magnesium was fully gone and the there were not anymore gas bubbles to be seen, the reaction was complete.
Placing a finger back onto the whole of the stopper and the gas buret removed from the stand, the buret was transported to the sink where it was placed inside a large graduated cylinder. The volume of the gases were measured and recorded. ?After recording the volume, the liquids inside the buret were poured into the 600mL beaker containing the water. The content of the beaker was poured in the sink and the beaker was filled again with more tap water for the next trial. ?The beaker was rinsed thoroughly with distilled water and placed back on the stand until ready for the next trial. The procedure was done twice more. After finishing all three trials, the beaker and graduated cylinder were cleaned with soap and put away. The gas buret was carefully washed and turned back in to the lab technician. Observations: To begin with, when the magnesium was measured it was sturdy, shiny and visible. However, when the magnesium was placed inside the buret with distilled water, blue dye and hydrochloric acid, gas bubbles began to appear and in just minutes, the magnesium disappeared. Also, at first when placing the blue dye inside the gas buret the liquid was blue.
But when hydrochloric acid was poured into the buret with the dye, the liquid appeared to be a dirty orange brown color. Then, once filling the buret with distilled water the different layers of the density of hydrochloric acid was visibly seen. The darker color was towards the bottom and glancing at the top the color lightened up to a light green to almost colorless. When the buret was turned upside down the hydrochloric acid was noticeably seen moving down, due to the dark liquid moving lower. It was known when the hydrochloric acid reached the magnesium strip because the magnesium began to give off bubbles.
Results and Discussion: The final results calculated, which was the molar volume, for the three trials completed turned out to be all 22. 9L. This was very close to the actual molar volume which was 22. 4L with only being 0. 5L off. For the gas constant, the average value of R calculated was 0. 0841 L atm/K mol. The result obtained was higher than the literature value of R which was 0. 08206. The result obtained had to due with the error involving air bubbles forming before the actual reaction began. This would make the amount of liters larger and then when calculating the value for R, it would make the value for R larger.
Had there have been no air bubbles the volume of hydrogen would have been closer to the literature value of R. Also, when transferring the gas buret to the sink where the larger graduated cylinder was held, some of the liquid inside the buret was lost and more air bubbles were formed. This would increase the volume and would increase the value of the gas constant to be higher than it should. Since the actual molar volume was known and since the average obtained in doing the experiment was fairly close, this experiment was an excellent way to show the relations between the volume and moles of a gas.
One way to improve this experiment is to create a better stopper for the gas buret so that when inverting the gas buret and transporting it, the liquid inside would not pour out and a finger would not have to be used to prevent any liquid from escaping but it would somehow still be able to drain the excess liquid out of the buret. Refereneces: 1)Southwestern College, Chem 170 CER Lab Manual, Cengage Learning, Michael Stranz, 2008, Pg. (67). 2)Mark Cracolice and Edward Peters, Basics of Introductory Chemistry, Brooks/Cole Belmont CA, Jay Campbell, 2007, 393.
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