Properties Of Gases Lab Report 3vwz

Act B4 Properties and Relationships of Gases Lab Report Name: __________________________________

Date:

During the lab you collected both qualitative and quantitative data on the properties of a gas. In the following you will examine the data you collected during the lab and complete an analysis. PART I: The Relationship between Temperature and Volume in an Ideal Gas You varied the temperature of the gas inside the test tube by heating the test tube with a Bunsen burner. During heating, the temperature of the gas inside the test tube increases, where temperature is a measure of the average velocity of the molecules of gas. You marked the original height of water inside the test tube before heating and then observed the relative change in the height of the water during heating as shown in the two models. The change in the water height is directly related to the change in volume of gas inside of the test tube. Suppose you wanted to further investigate the relationship between temperature and volume of gas. You plan to heat the test tube for different lengths of time measured in seconds. Your independent variable in this experiment, temperature of gas, while not directly measured, will be related to the length of time the test tube is heated. You need to develop a method to quantitatively measure the dependent variable, the volume of gas inside of the test tube, at the end of each heating time interval. When you select a piece of equipment to complete a measurement, you need to consider the precision needed to complete a task. For example, if you need to determine whether the mass of two objects are different to within the ones place (±1 g), then a centigram balance could be used to measure mass. In Part II of this activity, you created a ‘tape ruler’ to measure the change in water height. This ruler used a 1 mm scale and was placed at the open end of test tube, as shown in the figure to the right. This tape ruler could be used in Part I but the length would need to be increased to span the length of the test tube.

Consider the possible ‘tape rulers’ shown at left that could be used to measure change in water height. The scales on the rulers are 1 mm, 2 mm, 5 mm and 10 mm.

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1. Which of the tape rulers could be used to measure change in water height at the end of each heating time interval in the new experiment? Select all that apply:

 1 mm scale

 2 mm scale

 5 mm scale

10 mm scale

2. Which tape ruler would you select to use for the new experiment? The 10 mm scale, because the change in volume of the gas can not be covered with a smaller tape ruler. Explain your reasoning for the tape ruler you choose above.

Imagine you have a magnifying glass that allows you to view the molecules of gas in a small volume inside the test tube as it is being heated. The model shows both the macroscopic perspective with the test tube and water height, plus a microscopic or particulate illustration of the gas molecules in a small volume inside the test tube. Consider the particulate model shown below that illustrates the gas molecules inside a very small volume of the test tube as it is being heated. Models are drawn to illustrate the primary features, or components, of the object being modeled.

The components used in these two models to illustrate the changes that occur during heating include: - the number of gas molecules inside the small volume - the 'velocity' lines to represent the average velocity of the gas molecules - the size of the circle used to represent the gas molecules - the color of the circles used to represent the gas molecules - the size of the box used to represent the small volume inside the test tube Some components in a model are required because they are necessary to illustrate a specific aspect of the phenomenon; these can be labeled as major components of the model. Other components are not required and can generally be altered or omitted without changing the purpose of the model; these can be labeled as minor components of the model. 3. Identify the MAJOR components you need in the models in order to illustrate the changes at the particulate level when the gas inside the test tube is heated. Select all that apply.  the size of the box used to represent the small volume inside the test tube the number of gas molecules inside the small volume  the size of the circle used to represent the gas molecules  the color of the circles used to represent the gas molecules

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the length of the 'velocity' lines to represent the average velocity of the gas molecules PART II: The Relationship between Pressure and Volume in an Ideal Gas In Part II, you varied the pressure of the gas inside the test tube by raising and lowering the test tube inside the large beaker and observed the change in the height of the water inside the test tube. Pressure is equal to force per unit area, P = force/area. The pressure of the gas inside the test tube, Pgas, is a measure of the amount of force of the gas molecules hitting the area of the walls of the test tube and the surface of the water. When the test tube is positioned in the beaker such that the water height in the test tube is equal to the water height in the beaker, then Pgas is equal to the external pressure, P atm, of the molecules of air in the room hitting the surface of the water in the beaker. Consider the two models below showing the test tube positioned with the open end near the top of the water inside the beaker (Model #1) and with the test tube lowered inside of the beaker (Model #2). 4. What is the relative difference between Pgas and Patm in Model #1?  Pgas = Patm

 Pgas > Patm

Pgas < Patm

5. What is the relative difference between Pgas and Patm in Model #2?  Pgas = Patm

Pgas > Patm

 Pgas < Patm

Boyle’s Law states that the pressure of a gas is inversely proportional to its volume (as pressure increases, volume decreases) under conditions of constant temperature and constant amount of gas. You varied the pressure of the gas inside the test tube by raising and lowering the test tube inside the large beaker. Consider the following model of the test tube positioned in the beaker such P gas = Patm, where the water height inside the test tube is equal to the water level in the beaker. In Model #2, the test tube was lowered such that the water height inside the test tube is lower than the water level in the beaker.

6. Which of the following represents the predicted change, based on Boyles' Law, for the water height inside the test tube for Model #2?

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  7. Examine the Part II data in the Class Data file provided for the lab report. Did the experimental data collected by students’ the outcome for Vgas predicted by Boyles’ Law when the test tube was lowered in the beaker as shown in Model #2? Yes - most of the class data showed that Vgas decreased which was predicted by Boyles’ law.  Yes - most of the class data showed that Vgas increased which was predicted by Boyles’ law.  No - most of the class data showed that Vgas decreased which was not predicted by Boyles’ law.  No - most of the class data showed that Vgas increased which was not predicted by Boyles’ law.  Other - explain

8. What percent of the data in the Class Data file for Part II ed the outcome for V gas predicted by Boyles' Law?

Part II: Total number of data sets:

28

Number of data sets that prediction for Vgas: Percent of data sets that prediction for Vgas:

28 100

PART III: The Relationship between Mass and Volume in an Ideal Gas In Part III, you varied the amount of the gas collected inside the buret by varying the mass of magnesium reacted with hydrochloric acid. You measured the change in the height of the water inside the buret, and then calculated the volume of gas. If you examine the Class Data file, you may find several cases where a set of data recorded by a student is incomplete. For example, data may be missing for the mass of magnesium or for temperature. Incomplete data sets cannot be used in any analysis so you’ll need to identify the set of complete data from the Class Data file you’ll use for analysis. 9. Number of complete data sets collected for Part III: ___72______ Analyze the complete data set in the class file from Part III to determine number of observations (i.e., number of data rows) with a mass of magnesium in a given range.

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10. Provide the value for the smallest and the largest experimental volume of gas collected within that range of mass. Calculate the average volume of gas collected within each mass range. Table 1. Experimental Volume of Gas, VExpt, as a function of mass of Mg Range in Mass of Mg (±0.0001 g) 0.0040 – 0.0081 – 0.0121 – 0.0161 –

0.0080 0.0120 0.0160 0.0200

Number of Observations

Smallest Experimental Volume of Gas (±0.05 mL)

Largest Experimental Volume of Gas (±0.05 mL)

Average Experimental Volume of Gas (±0.05 mL)

22 27 11 10

4.70 8.37 12.30 14.70

22.13 18.00 21.50 21.80

10.24 12.63 17.09 18.39

Use a graphing program (e.g., Excel) to plot the complete set of data from Part III. 11. Plot the dependent variable (y-axis) versus the independent variable (x-axis) using the complete data set. Attach this graph to your lab report. Be sure to properly label your graph.

Total Volume of Gas Collected (+/- 0.05 mL) 25.00 20.00 15.00

f(x) = 797.2x + 5.03 R² = 0.53 Total Volume of Gas Collected (+/- 0.05 mL)

Volume of gas collected (mL) 10.00 5.00

Linear (Total Volume of Gas Collected (+/- 0.05 mL))

0.00

Mass of Mg (g)

12. For one of your samples of magnesium, use the balanced chemical equation to convert the mass of magnesium to the number of moles of hydrogen gas evolved, n H2. Use the ideal gas law to convert n H2 to the volume of hydrogen gas produced, VIdeal Assume that the temperature of the gas inside the buret is equal to

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room temperature (Tgas = Troom) and the pressure of the gas inside the buret is equal to atmospheric pressure in the room (Pgas = Patm). Show your work.

Mg ( s ) +2 HCl ( aq ) → H 2 ( g )+ MgC l 2 (aq) Moles of hydrogen gas obtainable

¿ 0.0092 g Mg ×

1 mol H 2 ( g) 1mol Mg × =0.0003785 2 mol 24.305 g Mg 1 mol Mg

Volume of hydrogen gas

0.0003785 2 mol × 0.082055 ¿

L . atm ×295.5 K mol . K

1 atm

×

1000 mL =9.18 mL 1L

13. Compare the relative difference of the experimental volume of gas, V Expt, to the theoretical volume of gas, VIdeal, predicted by the Ideal Gas law for your sample of magnesium. Select the statement that applies to this sample. VExpt > VIdeal

 VExpt < VIdeal

 VExpt = VIdeal (within ±0.05 mL)

You can further describe the data collected in Part III by determining the number of observations (i.e., rows of data) in which VExpt was different from VIdeal to within 0.05 mL. 14. Complete the following table to analyze the complete set of data collected in Part III; determine both the number of observations and percent of observations for each value of the variable. Table 2. Comparison of Volumes of Gas, VExpt and VIdeal, in Part III Data Variable: Comparison of VExpt to VIdeal

Number of Observations

Percent of Observations

VExpt > VIdeal

56

77.8

VExpt < VIdeal

15

20.8

VExpt = VIdeal (within ±0.05 mL)

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1.40

15. Based on the class data, is VExpt consistently different from the predicted value, VIdeal? Describe the pattern in the data. Majority of the data has VExpt > VIdeal. A reverse trend has been observed in about 20% of the data. Only one experimental volume matched with the ideally expected volume. Overall, the data showed a linear pattern, with the volume of hydrogen gas increasing with increase in the mass of magnesium. Experimental data may not match predicted outcomes based on theoretical relationships, such as stoichiometry calculations that involve the ideal gas law, for a number of reasons.

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16. For the following potential sources of error in the methods used in Part III, determine how the error would impact VExpt (i.e., values would be too large, too small, or not changed). Errors in VExpt: Error #1: IF the gas inside the buret was not cooled to room temperature before measuring volume THEN Tgas > Troom too large ☐ too small ☐ not changed

AND the impact on data: VExpt would be

Error #2: IF the buret was not positioned within the large beaker of water such that the water level inside the buret was equal to the water level inside the beaker THEN the relative pressure of gas inside the buret does not equal P atm. AND the impact on data: VExpt, if Pgas > Patm would be: ☐ too large AND the impact on data: VExpt, if Pgas < Patm would be:

too small ☐ not changed

too large ☐ too small ☐ not changed

In Part III the hydrogen gas produced from the reaction of magnesium and hydrochloric acid was collected by displacing water from a buret. The gas inside of the buret is actually a mixture of H2 and H2O because of the evaporation of water to a gas from the liquid water inside the buret, as shown in the model. In this case, the pressure of the gas inside the buret is the sum of the partial pressure of each gas: Pgas = PH2 + PH2O. The calculation of VIdeal using the balanced chemical equation and the ideal gas law assumes that only hydrogen gas was inside the buret, with P gas = PH2. Error #3: The gas inside the buret consisted of water gas, H 2O, and hydrogen gas, H2, not just H2. IF ☐ Pgas > Patm, THEN the impact on data: VIdeal would be: ☐ too large IF ☐ Pgas < Patm, THEN the impact on data: VIdeal would be:

too small ☐ not changed

too large ☐ too small ☐ not changed

Outliers are data points on graphs which do not represent the pattern shown by other data points. On the graph you constructed for Part III, determine if there is a pattern in the outlier data. 17. The pattern in the outlier data have values for VExpt which are consistently: too large

☐ too small

☐ there is no pattern

18. Which one of the errors described above is the most important in of explaining why VExpt is different from VIdeal? Error #1

☐ Error #2

☐ Error #3

19. Which one of the errors described above is the least important in of explaining why VExpt is different from VIdeal? ☐ Error #1

☐ Error #2

Error #3

Conclusion

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Overall, the experiment succeeded in showing that temperature and pressure for an ideal gas at constant volume and mass follow the relation of the ideal gas equation. Differences existed in the experimental graph of temperature versus and pressure and the theoretical curve of temperature versus pressure. These differences, however, can be ed for by experimental error.

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