LAB Report 10 - Determination of the Gas Law Constant PDF

Preview

Summary

Determination of the Gas Law Constant...

Description

General Chemistry I, SCC 201 Lab Report #10 Determination of the Gas Law Constant Prof. Amelita Dayao Student’s name: Luis De la Cruz

A. OBJECTIVES



To determine the value of the universal gas constant, R.

B. MATERIALS

Equipment: Balance, tweezers, 25x200 mm boiling test tube, Syringe, barometer, 2x100mL glass beakers, 10mL pipet, pipet pump, glass tubing bent, 2 ring stands, 2 utility clamps, rubber stopper, Tygon tubing, thermometer. Chemicals: 1.0M HCl, 0.1M HCl, Magnesium metals.

C. PROCEDURE

1. The utility clamps and the ring stands were constructed and the syringe and the boiling test tube were set up on the utility clamps. Then, the syringe with the tygon tubing and the boiling test tube were connected with glass tubing bent for collecting hydrogen gas. 2. The barometer pressure was recorded by using barometer and room temperature was recorded by using thermometer. 3. The 0.1M HCl and 1.0M HCl were place into each of 100 mL glass beakers. 4. The magnesium metal was dipped into the 0.1M HCl by using the tweezers to remove the magnesium coating. The tweezers could not be allowed to have a contact with the solution. 5. After the surface of magnesium totally looked grayish or silvery white color, it was rinsed with distilled water and dried with a paper towel. 6. The magnesium was weighed approximately 0.016 – 0.018 g. 7. 4 mL of 1M HCl was placed into the boiling test tube with using the 10 mL pipet. 8. Then, the magnesium that was already weighed was transferred inside wall of the boiling test tube with the HCl solution that was tilted without touching the HCl solution. 9. While the rubber stopper was inserted carefully into the tube, the tube was rotated to allow the magnesium to slide down into the solution. 10. Before the final volume of the pressure was recorded in the syringe, the reaction was needed to wait for 5 minutes to equilibrate.

11. The process for 1 to 10 was repeated for the second test. The solution was replaced with the same solution without rinsing the test tube with the distilled water.

D. DATA, CALCULATIONS AND GRAPHICS

Determination

1

2

3

4

0.0145

0.0162

0.0140

0.0144

Moles of Mg (mol)

0.000597

0.000667

0.000576

0.000592

Moles of H2 (mol)

0.000597

0.000667

0.000576

0.000592

Initial syringe volume (mL)

0.0

0.0

0.0

0.0

Final syringe volume (mL)

14.0

16.0

14.0

14.0

Volume H2 (mL)

14.0

16.0

14.0

14.0

Volume H2 (L)

0.014

0.016

0.014

0.014

Temperature (˚C)

22.0

22.0

22.0

22.0

Temperature (K)

295

295

295

295

Barometric pressure (mm Hg) Vapor pressure of water (mm Hg) Corrected pressure (mm Hg)

767

767

767

767

19.83

19.83

19.83

19.83

747.17

747.17

747.17

747.17

Corrected pressure (atm)

0.983

0.983

0.983

0.983

0.07814

0.07993

0.08099

0.07880

Mass of Mg (g)

R value (L.atm/K.mol) Average R Value (L.atm/K.mol) True value of R (L-atm/mol-k) Percentage error (%)

Calculations:

0.07947 0.08205 3.14 %

The actual value of gas constant is 0.08205 L.atm/K.mol and 1atm = 760 mm Hg Mg(s) + 2 HCl(aq)  MgCl2(aq) + H2(g) 

Number of moles Mg: Mol Mg = Mass of Mg x 1 mol / 24.305 g 1* Experiment = 0.0145 g x 1 mol / 24.305 g = 0.000597 mol 2* Experiment = 0.0162 g x 1 mol / 24.305 g = 0.000667 mol 3* Experiment = 0.0140 g x 1 mol / 24.305 g = 0.000576 mol 4* Experiment = 0.0144 g x 1 mol / 24.305 g = 0.000592 mol Note: Since Mg and H2 have the same ratio in the chemical equation, both have the same number of moles.



Conversion of mL to L Conversion = (mL) (1L / 1000mL) = 14.0mL x (1L/1000mL) = 0.014L Conversion = (mL) (1L / 1000mL) = 16.0mL x (1L/1000mL) = 0.016L



Corrected pressure: Co. Pres. = Barometric pressure - Vapor pressure Co. Pres. = 767 mm Hg - 19.83 mm Hg Co. Pres. = 747.17 mm Hg  747.17 mm Hg x 1 atm / 760 mm Hg = 0.983 atm



Temperature in Kelvin unit T = 273 K + ˚C T = 273 K + 22.0 T = 295 K





The gas constant (R) 1* R = P . v = N.T

0.983 atm x 0.014 L = 0.07814 L.atm/ K.mol 0.000597 mol x 295 K

2* R = P . v = N.T

0.983 atm x 0.016 L = 0.07993 L.atm/ K.mol 0.000667 mol x 295 K

3* R = P . v = N.T

0.983 atm x 0.014 L = 0.08099 L.atm/ K.mol 0.000576 mol x 295 K

4* R = P . v = 0.983 atm x 0.014 L = 0.07880 L.atm/ K.mol N.T 0.000592 mol x 295 K The average of R

The sum of trial of R = 0.07814 + 0.07993 + 0.08099 + 0.07880 The sum of trial number 4



= 0.07947 L.atm/ K.mol Percentage error = | the accepted value – the experimental value | x 100 % the accepted value = | 0.08205 L.atm/ K.mol - 0.07947 L.atm/ K.mol | x 100% 0.08205 L.atm/ K.mol = 3.14 %

E. DISUSSION

Results Obtained Gases are the third normal state of the matter. Some element and molecular compounds are gases at R, T, and normal pressure. Commonly, gases are characterized by four physical properties, such as volume which is the amount of space that gas occupies in Liters; moles of the gas; temperature which measure the average kinetic energy of gas molecule in Kelvin; and the pressure which is the force that exerted by gas molecules as the molecules collide with wall in an enclosed container in atmosphere. The scientists who study gases discover V α 1 /P as Boyle's Law states that the volume of a gas sample is proportional to the inverse of its pressure at constant temperature, V α T as Charles' Law showed that the volume of a gas sample is proportional to its absolute temperature at constant pressure, and V α n as Avogadro's Law states in effect that the volume of a gas sample is proportional to the number of moles of gas. The combination of three proportional laws give the equation such V α nT/P.

In this experiment, the reaction of magnesium metal with hydrochloric acid to produced magnesium chloride and hydrogen gas was to find the gas law constant.

Mg(s) + 2 HCl(aq)  MgCl2(aq) + H2(g) The room temperature and the barometer pressure were constant. After the volume of hydrogen gas was founded by collecting the gas in the syringe and the number moles was also found by using the molar mass. The gas constant (R) could be determined by using the ideal gas law

from the three proportional equations which was given R = P.V/ n.T. As a result, the gas law constant was obtained which was 0.07814 L.atm/K.mol for the first trial, 0.07993 L.atm/K.mol for the second trial, 0.08099 L.atm/K.mol for the third trial and 0.07880 L.atm/K.mol for the fourth trial. Then, the average of the both trials could be determined which was 0.07947 L.atm/ K.mol. As the average of the trials was compared with the actual value of gas constant which was 0.08205 L.atm/K.mol, thoroughly, the percentage error of this experiment little bit high because of several factors which was 3.14 %. Therefore, the method of this experiment with using the syringe to acquire the volume of the gas was not 100% accurate. However, this method was still useful to know how to determine the result of the gas law constant, where R, T, and normal pressure were the main figure of the R.

Errors There were several factors that affected this experiment to the accuracy of the calculations. The concentration of the solution might be contaminated or it might not be 100 % perfect due to many users. Also, the instrumental measurements that were used were not always in perfect condition, such as the balance which might not read correctly the weight of magnesium metal because it was the limited reagent for the experiment, and the barometer which might not read correctly the atmospheric pressure. The rubbers might already lose the elasticity. It was part human error when it came to read the manual scale of the instruments such as the glass beakers, the syringe or the pipet. Precautions

To reduce the error of measuring, when transferring the solution from the pipet to the boiling test tube, wait 20-30 more second to drain the solution so the volume of the solution was more accurate. After rinsing the magnesium metal with distilled water, it should be dried with a paper towel. The glass around the balance should be closed when measuring the weight of the magnesium metal to reduce the air flow. Also, the balance should read zero with the wax paper before the metal was placed on the top of it. The pipet should be rinsed with the standard solution of 1M HCl to avoid contamination. The HCl solution was corrosive and toxic and it should be avoided to contact with the skin. When the metal was dipped into the HCl solution by using the tweezers, the tweezers should not contact with the solution because the tweezers would contaminate the hydrochloric acid solution and the solution could not perfectly remove

the magnesium’s coating. When the syringe with the tygon tubing was set by using the utility clamp on a ring stand, its position should be connected straight horizontally. The boiling test tube should remain titled so it prevented the magnesium from sliding into the HCl solution when it was put inside the wall of the tube or it meant that if the magnesium were to slide into the HCl in the boiling tube before the system was sealed off, because the magnesium metal would react with the HCl or the reaction would proceed and some the hydrogen gas product would be lost and the result would not accurate. The syringe could be recorded for at least 5 minutes when the reaction allowed the system to equilibrate because 0.0145 grams of magnesium metal should completely react with the volume solution of HCl.

CONCLUSION As a result of this experiment, the reaction of magnesium metal with hydrochloric acid to produce hydrogen gas and magnesium chloride gave the value of the constant gas which was 0.07947 L.atm/ K.mol. Therefore, since the percentage error was too small (3.14 %), it was proved that this evaluation method or experiment gave the satisfactory results for the gas law constant.

F. REFERENCE

Brown, Theodore L.; LeMay, H. Eugene; Bursten, Bruce E.; Chemistry: The Central Science, 11th Edition, Prentice-Hall, 2008.

Miller, D. (2013) General Chemistry I Laboratory Manual.Kendall Hunt.

Miller, Dionne A. (Second Edition.); SCC201 Fundamentals of Chemistry Laboratory Manual; Cengage Learning, 2009, pp 25 – 32....