Gas laws lab final copy PDF

Preview

Summary

Download Gas laws lab final copy PDF

Description

0

1

Name:

Partner:

Student No: 2

Student No:

Lab Section: 017

Bench #: 32

Experiment 2: (1 week) (GAS) Gas Laws Purpose The goal of this lab is to witness how altering variables such as pressure, temperature, volume and amount (in moles) will affect the behaviour of an “ideal” gas. The Data derived from these sets of experiments should demonstrate a correlation between the variables in order to create a better understanding of universal gas laws.

Introduction The general behaviour of gasses can easily be predicted through the use of universal gas laws and formulas. While many of these laws stem from the research of 16th-18th century chemists 1 , they remain accurate and are often employed in modern day applications. Gasses can be manipulated through the alteration of variables such as; gas pressure (P), temperature (T), volume of container (V) and amount of gas in moles (n). Many of these variables have relationships with each other, and it is these relationships that are the foundation of universal gas laws such as the ones listed in table 1. Table 1 Gas Law Formula Relationship description 1 Boyles law k=PV The pressure of a gas is (k is a “proportionality inversely proportional to its volume, if its temperature constant”) remains the same. Gay-Lussac’s Law2 k=P/T The pressure of a gas is directly proportional to its temperature, provided the volume remains consistent. Daltons Law3 Ptotal=P1+P2… The total pressure of gas in a system is equal to the sum of the partial pressures of each individual gas. The combination of these laws along with several others, produces a formula known as the Ideal gas equation; PV=nRT. This formula encompasses all of the listed variables, along with a gas constant (R) that has many different values but is most commonly expressed as 8.314 J/K(mol). In order for this formula to be applicable, we must assume that the experimental gas has the properties of an “ideal gas”, however; a gas is never truly ideal in real world applications. Ideal gasses are said to have no volume to their gas molecules, and no intermolecular forces acting between those molecules. While this is impossible criteria for actual gasses, under the correct conditions many gasses can behave extremely similar to an ideal gas. 4 1 2 3 4

0

2

Procedure5 Part 1 •

To begin, a gas syringe was filled with 10.0 ml of air and attached to a pressure sensor through plastic tubing. The syringes pressure was then immediately recorded. Following this, the piston was pushed down to the 7.5ml mark, then 5.0 ml, and the pressure at each of these increments was recorded.

•

The piston of the empty syringe was then pulled out to 15.0ml and the pressure was recorded. The syringes volume was then increased in increments of 2.5ml until it was filled completely with 20ml of gas. The pressure at each increment was measured and recorded.

Part 2 •

A rubber stopper-flask assembly containing a pressure sensor was first prepared using a 125ml Erlenmeyer flask.

•

The flask was then inserted into a boiling water bath and tongs were used to secure the flask in order to achieve consistent temperature throughout. The temperature was measured using a temperature probe and recorded.

•

The pressure was measured by a pressure sensor included in the apparatus; this measurement was also recorded.

•

The same process was then repeated several times using a hot water bath, a room temperature bath, and an ice bath.

Part 3

5

•

First, about 0.10g of sodium bicarbonate was measured using a balance, and contained in a 125ml Erlenmeyer flask. The actual measured mass was recorded.

•

The flask was then attached to a stopper assembly containing a pressure sensor and put into a warm water bath. The pressure and temperature of the flask were measured and recorded.

•

Simultaneously, 20ml of 1M acetic acid was added to a syringe, which was then attached to the stopper-flask assembly.

•

The Acetic acid was injected into the Erlenmeyer flask, and swirled in the room temperature bath until a stable pressure was achieved, at which point the pressure and temperature of the flask was recorded.

0

Questions Part 1

1. Based on your data, what would you expect the pressure to be if the volume of the syringe was increased to 40.0 mL? Explain or show work to support your answer. Based on a qualitative view of figure 1, It can be determined that increasing the volume of the syringe to 40ml would significantly decrease the pressure within that vessel. This is also demonstrated by the values in table 1, as it can be seen that the pressure within the syringe decreases with an increase of volume. 2. Find the proportionality constant, k, from the data. If this relationship is direct P=kV, then k = P/V. If it is inverse P=k/V, then k = P×V. Based on your data, Calculate k for both equations and then indicate which formula gives the answer that is “constant” for all your P,V data pairs. Choose the correct one of these formulas and calculate the average k value for the seven ordered pairs in your data table (divide or multiply the P and V values). Calculate is the uncertainty, i.e. standard error, in this final mean value of k? (Use statistics; see the section on determining this in the introduction part of the lab manual) Through analyzing the k values for both k=PV and k=P/V, it can be determined that the relationship between pressure and volume is inverse. Through use of the k values determined for each data point, and the equation k=PV, the average proportionality constant was found to equal 10.8609 with an uncertainty of ±0.2097.

3

0

4

Part 2

1. In order to perform this experiment, what two experimental factors were kept constant? Both the volume of the flask, and the amount of gas (in moles) remained the same throughout the experiment. This allowed for isolation of the temperature and pressure variables in order to observe their relationship. 2. Write an equation to express the relationship between pressure and temperature (K). Use the symbols P, T, and k. K=P/T 3. Find the proportionality constant k. Like above, if the relationship is direct, k = P/T. If it is inverse, k = PxT. Based on your answer to Question 2, choose one of these formulas and calculate k for the four ordered pairs in your data table (divide or multiply the P and T values). Show the answer in the fourth column of the Part 2 data table. How “constant” were your values? The equation k=P/V was used in order to calculate the proportionality constant k. after applying the equation to each data set, it was found that calculated constants of all 4 baths were relatively similar, differing by an average of about 0.004257. The similarity of the calculated constants, along with the curve in figure 2 prove this relationship to be direct. 4. The data that you have collected can also be used to determine the value for absolute zero on the Celsius temperature scale. On the plot of Celsius temperature on the y-axis and pressure on the x-axis, find absolute zero. Figure 4

Temperature vs Pressure 200

Temperature (°C)

150 100 50

y = 141.87x - 37.943

0 -50 0 -100

0.2

0.4

0.6

0.8

1

1.2

1.4

-150 -200 -250 -300

Pressure (atm)

The absolute zero Is demonstrated by the y intercept, or “b” value in the linear equation y=mx+b. The equation of the linear trendline (dotted line) in figure 4 was found to be y=141.87x-37.943,

0

through the use of excel technology. The b value of this equation must then be equal to -37.943, which is representative of the absolute zero of the data collected in this lab. 5. Since “absolute zero” is the temperature at which the pressure theoretically becomes equal to zero, the temperature where the regression line (the extension of the temperature-pressure curve) intersects the y-axis (b in the y=mx+b equation) should be the Celsius temperature value for absolute zero. What is your experimental value for absolute zero? What is the uncertainty (do a visual estimate based on your plot)? Is your answer correct, i.e. does the real value lie within the limits of your experimental uncertainty? Based of the equation of the trendline in figure 4, the experimental absolute zero is equal to -37.943 °C. The uncertainty in the slope could be estimated to be about ±5. Using this uncertainty, the range of temperature for absolute zero would be between -32.943 to –42.943 °C. The accepted vale of absolute zero is equal to -273.15 °C , which means that the calculated answer is incorrect as the literature value falls very far outside of the experimental range of uncertainty.

Part 3

1. Complete the data sheet and show all calculations in your notebook. Through the application of initial data in the Ideal Gas equation, the initial amount of gas was found to equal 0.064 mol ± 0.0615 mol. Through a similar process using final data, the amount of CO2 added was calculated as 0.011 mol±0.0106 mol. Note that the uncertainty values for the pressure and temperature variables have been retrieved from the measurement instruments website. 6 7

6 7

5

0

2. Use Dalton’s law to determine the partial pressure of the CO2 formed. Through use of the Daltons law formula, the Partial pressure of CO2 in this data was calculated as 0.17558 atm with an uncertainty value of ±0.33058 atm.

3. Based on the known values: partial pressure (pressure change seen during the reaction), the volume of the flask, the number of moles of CO2 (found using mass of sample and molar mass of NaHCO3) and the final temperature in Kelvin (conversion: T in Celsius + 273.15) what is the value of the gas constant R? – Don’t forget units. Use PV=nRT and solve for R. Determine the uncertainty in R. By determining the value of each variable within the ideal gas equation, the R value was calculated through algebraic isolation. The gas constant was found to equal 8.3117 J/K(mol) with an error propagation of ±16.93 J/K(mol).

6

0

7

4. Compare this value to the accepted value. (8.3145 J K-1 mol-1). In this context, compare means that you should determine if the literature value for R agrees with your experimental value within your limits of uncertainty. The calculated R value is extremely similar to the accepted value of 8.3145 J K-1 mol-1 and falls well within the range of the calculated uncertainty. This indicates that the gas observed in this experiment exhibited almost perfectly the behaviour of an ideal gas.

DATA SHEET Part 1

Table 2 Volume (mL)

Pressure (atm)

Constant, k P•V

P/V

5.00

1.9939

9.9695

0.39878

7.50

1.3681

10.2608

0.18241

10.0

1.0679

10.6790

0.10679

12.5

0.8756

10.9450

0.07005

15.0

0.7440

11.160

0.04960

17.5

0.6563

11.485

0.03750

20.0

0.5777

11.554

0.02889

Figure 1

Volume v.s Pressure Pressure (atm)

2.5 2 1.5 1 0.5 0 0

5

10

15

Volume (ml)

20

25

0

8

Part 2 8

Table 3 Water Bath

Boiling

Hot

Room temp

Ice

Pressure (atm)

Temperature (°C)

Temperature (K)

Constant, k (P / T or P•T)

0.9873

100.0

373.15

0.002646

0.5614

47.7

320.9

0.001750

0.4398

28.6

301.8

0.001457

0.3861

8.80

282.0

0.001369

Pressure vs Temperature Pressure (atm)

2.5 2 1.5 1 0.5 0 0

100

200

300

400

Temperature (K) Figure 2

Pressure vs Temperature Pressure (atm)

2.5 2 1.5 1 0.5 0 0

20

40

60

80

100

120

Temperature (°C ) Figure 3

8

0

Part 3

Mass of NaHCO3: 0.123g Volume of flask: 149ml Temperature (initial): 22.4˚C Temperature (final): 22.8˚C Pressure (initial): 1.0444atm Pressure (final): 1.2260atm Amount of gas initially in flask: 0.064 mol Amount of CO2 added: 0.011mol

9

0

10

References 1.Petrucci, R. H. (2017). Chapter 6-3. In General chemistry principles and modern applications (11th ed., pp. 206–207). Upper Saddle River, NJ: Pearson. 2. Libretexts. (2019, June 5). 14.5: Gay-Lussac's Law. Retrieved October 3, 2019, from

https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Book:_Introductory_Chemist ry_(CK-12)/14:_The_Behavior_of_Gases/14.05:_Gay-Lussac's_Law. 3.Libretexts. (2019, June 5). Dalton's Law (Law of Partial Pressures). Retrieved October 3, 2019, from https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps /Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Physical_Properties_of_Matte r/States_of_Matter/Properties_of_Gases/Gas_Laws/Dalton's_Law_(Law_of_Partial_Pressures). 4.Page 47 of the first year lab manual chem 112 5.page 49-51 of the first year lab manual chem 112 6. Go!Temp. (n.d.). Retrieved October 4, 2019, from https://www.vernier.com/products/sensors/temperature-sensors/go-temp/. 7. Gas Pressure Sensor. (n.d.). Retrieved October 4, 2019, from https://www.vernier.com/products/sensors/pressure-sensors/gps-bta/.

8.Data retrieved from Katie Rorabeck, student number: 20145750, lab section 009 and partner Natalie Pothier, student number; 20147681, bench #33....