Evaluation of a gas law constant lab
Abstract: The result of the change in volume was approximately 22 CC or 0. 00084 mol. This translates into the average for the R constant being 83. 8L*atm/K*mol. The four determinations ensured that the results were accurate because more than one trial helps somewhat prevent error. Approximately 0. 20g of the Mg ribbon was used for these determinations. Introduction: 1. Theory If the temperature of a gas sample was held constant, its volume varied inversely with its pressure. The Kelvin scale is known as the absolute scale.
Charles’ law states that volume of a given mass varies directly with its absolute temperature if the pressure remains constant. Ideal gases are those whose behavior is exactly described by Boyle’s and Charles’ laws. Avagadro’s principle says that the volume of a gas sample at a given temperature and pressure is proportional to the mass or number of moles of the gas. 2. Reference citations Grover W. Everett, East Carolina University, Signature Lab Series, Prop 0332, p. 141 3. Important Equations V ? 1/P V=K1/P.
V=K2*T V ? T P1V1T1? P2VxT1? P2V2T2 Vx=V1(P1/P2) V2=Vx(T2/T1) V2=V1(P1*T1/P2*T2) P2*V2/T2=P1*V1/T1 PV/T=K PV=nRT Mg(s)+2HCl(aq)? MgCl2(aq)+H2(g) PV/nT=R PV/nT=atmosphere-millileter/mole-degree=R Corrected pressure, atm= ((recorded barometric pressure, torr – vapor pressure of water, torr)/760 torr atm^-1) 4. Objective In the experiment, one must determine the volume of a known mass of a gas at a measured temperature and pressure. One must use data to evaluate the universal gas law constant, R. Experimental: 1.
The procedure for this experiment appears in the lab manual1. Everett, G. W. ; Everett G. W. Jr. Classifying Matter by Properties; Cengage Learning: Manson, OH, 1997, pp 143-149. Results: Mass Mg, g0. 021g0. 021g0. 022g0. 020g # of moles Mg Initial syringe vol, mL4. 5 CC5. 0 CC19. 0 CC10. 0 CC Final syrine vol, mL26. 5 CC27. 3 CC43. 3 CC31. 0 CC Volume, H2 (g) mL22. 0 CC22. 3 CC24. 3 CC21. 0 CC Barometric pressure, torr754754754754 Vapor pressure of water, torr19. 82719. 82719. 82719. 827 Corrected pressure, atm0. 966 Temperature, C22222222.
Temperature, K295. 15295. 15295. 15295. 15 R, mL atm K^-1 mol^-184. 5 atm*mL/mol*K83. 8 atm*mL/mol*K83. 3 atm*mL/mol*K83. 5 atm*mL/mol*K Average R, mL atm K^-1 mol^-183. 8 atm*mL/mol*K Discussion: 1. Narrative The results relate to the theory because it illustrates the R constant that should be used from finding the volume of H2 from a syringe and also analyzing the temperature, barometric pressure, vapor pressure, and corrected pressure. Students participated in four determinations in which they witnessed the volume change in H2.
The objective was met because we accurately determined the value of R in mL*atm/K*mol. The determination of this figure was determined by calculating the number of moles from the mass and molar mass. The R was then calculated using this for n and then also the given values provided for P, V, and T in the equation PV=nRT. 2. Comparison to literary values The average value of R derived from the four determinations is 83. 8mL*at/K*mol and this matches the literary values. Sparknotes LLC, 2011.
3. Sources of error Error may of course occur if students incorrectly measure the change in volume, but there may be some other reasons. Because students took pre-made substances, there is a small chance that the substance they used was incorrectly made. The syringe pump may have been too tight, as in the case of our apparatus, which would prevent it from fully expanding to show the correct amount of volume change. Also, there may have been an error if the apparatus was not properly cleaned.