Experiment 2 behaviour of gases PDF

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Experiment 2 Behaviour of Gases

Abby Bettencourt 1006330249 Brianna Baker CHM110 – PRA102 TA: Nagina Amir Experiment performed: 30 / 09 / 2019 Report Submitted: 07 / 10 / 2019

Purpose The purpose of this experiment was to analyze the behaviour of gases through several methods. One method included a ribbon of unknown metal into a 3-inch tube that was placed into a gas burette (filled with 0.3M HCl), in which the gas burette was also placed into an 800/1000 mL beaker of 0.3M HCl. Through this method we were able to see how the metal forms a gas as it was reacted with 0.3M of HCl. Another method consisted of three measured tubes, for three trials, and on one end the tube a solution of 0.3M HCl was used to saturate the cotton ball, and the other end a solution of NH3 was used to saturate the cotton ball. Through this method we were able to analyze how fast each gas can travel by observing to see when a white ring would form, indicating that the two gases had collided. Experimental Method Part A, of the experiment of behaviour gases, begun with the preparation of an 800/1000 mL beaker, that was filled with 600ml of 0.3M HCl, and a 50 mL gas burette, which was also filled with 0.3M HCl (taken from the already filled 800/1000 mL beaker of 0.3M HCl. When filling the gas burette with 0.3M HCl, it was key to make sure that no bubbles were forming when pouring or else it would disrupt the experiment and the calculations. Moreover, it was especially important to look out for bubbles when flipping over the gas burette – so that the top was facing down into the 800/1000 mL beaker – which was why it was important to create a dome at the top of the gas burette when pouring the 0.3M HCl; so that no air becomes trapped. Once the first half of part A was prepared, then a 3-inch tube filled with distilled water (all the way to the top creating a dome) and the ribbon of an unknown metal was produced. However, before the ribbon of metal was placed into the tube, the metal was first cleaned with sandpaper to scrap off any contaminations that would affect the experiment or calculations in any way, and then weighted, for the use of later calculations. Consequently, when the 3-inch tube was filled with both the metal and the 0.3M HCl, the tube was then placed into the gas burette through the 800/1000 mL beaker, making sure that the gas burette does not come out of the HCl solution, and that the ribbon does not come out of the 3-inch tube. Once, everything was placed perfectly, with no bubbles or anything out of place, then the reaction begun to take place and observations were recorded. After the metal had completely dissolved, measurements of the volume of the gas burette and Δh of the solution levels were taken and recorded onto the data sheet. Once this half

of the experiment was finished, everything was cleaned and put away in the respective areas, and remaining observations were recorded. (1) Part B, of the experiment of behaviour of gases, begun with measuring the length of a tube, and recording the tube’s length onto the data sheet. The tube that was measured was then placed – in the fume hood – onto two adjustable clamps to hold the tube in a steady horizontal position. Once the tube was placed horizontally, one cotton ball was placed inside either end of the glass tube. Then, using a Pasteur pipette, the cotton ball at one end was saturated with HCl solution, while the cotton ball at the other end was saturated with NH3 solution, simultaneously. After the cotton ball was saturated, stoppers were placed on either side of the glass tube to allow for the gases to diffuse toward each other. Once a white ring was first spotted, it was marked on the glass tube, then either side was measured up to the point of the marker, making note of which end was HCl and NH3 solution. These measurements were then recorded onto the data sheet. Subsequently, this experiment of part b was repeated twice more then recorded. Immediately after part B was conducted, stations were cleaned and equipment was placed in respectable places, and final observations were recorded. (1) Results and Calculations Part A 1. Calculate the hydrostatic pressure in torr. Calculation of the hydrostatic pressure in torr. ρsoln h soln=ρ Hg hHg

h Hg=

ρsoln hsoln ρ Hg

(¿ 1.00 mLg ) ( 140 mm ) 13.6

g mL

1torr=1 mm Hg

10.3 torr ≈ 10.3 mm Hg

The calculated hydrostatic pressure in torr was 10.3 torr Hg.

≈ 10.3 mm 2. Calculate the total pressure of gas trapped in the burette. Calculation of the total pressure of gas trapped in the burette.

PH 2 + P H 2 O =Patm− Phydrostatic

¿ Patm− Phydrostatic−P H 2 O

¿ 759.5 torr −10.3 torr

≈ 749.2torr

Therefore, the total pressure of trapped in the burette was approximately 749.2 torr. 35

Pressure (torr)

30 25 20 15 10 5 0 14

16

18

20

22

24

26

28

30

32

Temperature (˚C) Figure 1. Indicates the graphed values of the vapour pressure of water (torr) at various temperatures (˚C) .

3. Calculate the pressure of the trapped H2 gas. Calculation of pressure of H2 trapped in the gas burette. P PH 2 + P H 2 O =pressure inside of burette (¿ ¿ atm−Phydrostatic )−P H 2 O PH 2=¿ (2) ¿ 749.5torr −19.24 torr ≈ 730.26 torr Therefore, the pressure of H2 trapped in the gas burette was approximately 730.26 torr. 4. Calculation of the number of moles of H2 using the Ideal Gas relation. Calculation of the number of moles of H2 using the Ideal Gas relation. ( 730.26 torr ) (0.0341 L) PV ¿ n H 2= PV =nRT L• torr RT )(295.2 K ) (62.364 mol • K −3

≈ 1.35× 10 mol

5. Calculation of the number of moles of the metal in the sample using the stoichiometry equation given M(s) + xH3O+  M+x (aq) + Assuming x = 2 M(s) + 2H3O+  M+2 (aq) + H2 (g) + 2H2O 1 mol M −3 n M ( s) =1.35 ×10 mol H 2 1mol H 2

(

)

x H2 (g) + xH2O. 2

Assuming x = 3 M(s) + 3H3O+  M+3 (aq) +

3 H2 (g) + 3H2O 2

−3

≈ 1.35× 10 mol M

−3

n M ( s)=1.35 ×10 mol H 2 −4

≈ 9.00 ×10 mol M

1mol M 3 mol H 2 2

( )

Calculation of the atomic mass (MM) of the metal. −3

−4

n M ( s) ≈ 1.35 ×10 mol M MM=

m n

¿

n M ( s)≈ 9.00 ×10 mol M

0.0327 g 1.35 ×10−3 mol

≈ 24.0

g mol

MM=

0.0327 g 9.00 ×10−4 mol

≈ 36

g mol

Identification of the unknown metal: Magnesium (Mg).

Part B 1. From your three sets of data, calculate the average distance diffused by HCl and by NH3. Ratio of Diffusion rates for the two gases, rNH3 / rHCl r NH 3 d avgNH 3 = r HCl d avgHCl ¿

26.17 cm 23.77 cm

¿ 1.10

2. Using these average distances and assuming that the distance travelled is directly proportional to the rate of diffusion, calculate the ratio of diffusion rates for the two gases, rNH3 / rHCl.

Calculations of the Average Distance of HCl and NH3 from the Data Obtained from Part B of The Experiment. Average Distance Diffused by HCl Average distance diffused by NH3

3.

(cm) 27.2 cm +25.8 cm+25.5 cm d avgNH 3= 3

(cm) 22.9 cm +23.9 cm+ 24.5 cm d avgNH 3= 3

¿ 26.17 cm

¿ 23.77 cm

Calculate the ratio of diffusion rates of these two gases that Graham’s Law predicts. Ratio of Diffusion Rates for the Gases That Graham’s Law Predicts. r1 M2 = r2 M1

√

√

r NH 3 M HCl = r HCl M NH 3

√

g g +35.45 mol mol ¿ g g ) 14.01 +3 (1.01 mol mol 1.01

≈ 1.46

4. Calculate the %deviation of your experimental result from the Graham’s Law prediction. %deviation from Graham’s Law Prediction 1.10 experimentalresult ¿ %deviation= ×100 % × 100 % ≈ 75.34 % 1.46 theoretical result Relatively high %deviation may indicate a relatively low precision.

Discussion

Regarding Part A, the experiment was done in one attempt since there was no formation of trapped air when filling up the gas burette with 0.3M HCl, and when converting the gas burette face down into the 800/1000 mL beaker solution of 0.3M HCl. However, when inserting the 3-inch tube of distilled water and the ribbon of magnesium into the gas burette, although the metal did not slip out of the gas burette and into the beaker of 0.3M HCl solution, it did float to the top of the gas burette. When the metal had done this I noticed the pace it was dissolving at was going at a slower rate compared to the person who sat next, whom started at the same time I did, but her metal was situated at the bottom of the 3-inch tube. Therefore, a suggestion, if this experiment was done again, would be to make sure that the metal stays situated at the bottom of the 3-inch tube in the gas burette, and compare how fast It would dissolve to the way the metal dissolved when it was at the top if the gas burette. Furthermore, using the result of the experiment and calculations, the unknown metal was identified as magnesium. Regarding Part B, the experiment went as expected; the white ring of ammonia chloride formed closer to the HCl solution since 0.3M HCl had a greater molar mass than NH3. Moreover, the ratio of diffusion for HCl, using the average distance traveled, was smaller than that of NH3, meaning that the collision happened much closer to the HCl. Hence, ammonia diffuses much faster than HCl, allowing for the NH4Cl fumes to form much closer to HCl, (3) proving the theory that lighter gases diffuse more quickly than heavier gases. The %deviation calculation yielded a percentage of approximately 75.34%. This deviation may have been due to looking at the average distance travelled, of HCl and NH3, and not measuring the time it took for the white ring to form. Graham’s Law was accurate if the temperature and the pressure between the gases were constant (4) Therefore, the temperature and the pressure may have been a factor to the results of %deviation. It was important to clean the metal ribbon because since magnesium was a reactive metal, and it does react with oxygen (creating magnesium oxide), due to this fact it was important to clean the ribbon of sandpaper to remove the magnesium oxide so that the experiment can be successfully performed.(5) Moreover, a white coating becomes formed onto the magnesium when it reacts with oxygen; hence, it was cleaned to remove

that coating so that it does effect the process of the experiment.(6) However, if the magnesium had not been cleaned, then the metal would not just be magnesium but magnesium oxide, in which atomic mass of magnesium and the atomic mass of oxygen automatically combine, creating a larger molar mass. Thus, in the experiment, if magnesium had not been cleaned, then the calculation to determine the metal would be much greater. Summary In this experiment, two parts (two different methods) were done to analyze the behaviour of gases. First method – Part A – included the use of a gas burette filled with 50 mL of 0.3M HCl, which was placed upside down into an 800/1000 mL beaker of 0.3M HCl, and a 3-inch tube filled with a ribbon of unknown metal and distilled water was inserted into the gas burette. The experiment took place when the metal met HCl. The formation in the gas burette was analyzed and recorded, and calculations were down to determine the unknown metal, which was magnesium. Second method – Part B – included the measuring of three open ended tubes (each for one trial), and a cotton ball on either end of the tube, saturated with either HCl or NH3¸ was used to in order to trap the two gases in the tube and determine which gas diffuses faster by looking out for a white ring – indicating that the collision was located at that spot. Moreover, trying to prove the theory that lighter gases (NH3) diffuse much faster than heavier gases (HCl), was in order. Hence, it was found that the white ring formed more closely to the HCl because of how slowly it diffused. Learning Objectives -

Ensuring that a metal ribbon was cleaned thoroughly and stays contained in the 3-inch tube, and not in the 800/1000 mL or else the reaction will occur outside the gas burette an we would be able to calculate anything.

-

Important to make sure that there was no air trapped within the gas burette or else it would mess up the calculations at the end.

-

Gas pressure inside the burette was not exclusive to the pressure of hydrogen gas, inside the gas burette, because the gas burette now contains water vapour, which was evolved due to the reaction taking place in the gas burette.

-

It was important to be aware that the before the official reaction of the experiment occurs that the metal does not encounter any HCl, or else a reaction will occur before the metal was even placed in the burette. Which was why the metal was contained in the 3-inch tube with distilled water.

-

There was no assumption that n = 1, because if a metal from the group 1 ion was used in the experiment, an explosion will occur due to how unstable the group 1 elements were.

References 1. Poe, J. In CHM110H5F: Chemical Principles I COURSE MANUAL’ Erindale College University of Toronto Mississauga, Ontario, 2019; pp 49-55. 2. Table 1. Vapor Pressure of Liquid Water between 15.0°C and 29.9°C. http://www.cabrillo.edu/~aromero/CHEM_30A/30A_Handouts/Vapor%20Pressure%20of %20Water%20(Activity%2015).pdf (accessed Oct 6, 2019). 3. Chapter 6.6: The Kinetic Energy of Gases. https://chem.libretexts.org/Courses/Prince_Georges_Community_College/General_Chemistr y_for_Engineering/Unit_3%3A_States_of_Matter/Chapter_6%3A_Gases/Chapter_6.6%3A_ The_Kinetic_Theory_of_Gases (accessed Oct 6, 2019). 4. Helmenstine, T. Graham's Law of Diffusion and Effusion. https://www.thoughtco.com/understand-grahams-law-of-diffusion-and-effusion-604283 (accessed Oct 6, 2019). 5. Pratap Singh, A. Why does the magnesium ribbon have to be cleaned before it’s used in an experiment? https://www.quora.com/Why-does-the-magnesium-ribbon-have-to-be-cleanedbefore-it-s-used-in-an-experiment (accessed Oct 6, 2019). 6. Science. https: //www.enotes.com/homework-help/why-should-magnesium-ribbon-cleanedwith-sand-182531 (accessed Oct 6,2019)....