CAS CH 101 Lecture Notes - Lecture 12: Intermolecular Force, Vaporization
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Question 11 pts
Which general statement about gases is NOT correct?
The molecules of a pure gas are distributed evenly throughout the container. |
Gases are much less dense than liquids or solids |
Molecules in a gas mixture can form layers according to their densities |
Gases can be compressed, even to the point of liquefaction |
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Question 21 pts
Which example is the greatest pressure?
1.00 atm |
101 kPa |
760 mm Hg (= 760 torr) |
All of the above pressures are equal. |
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Question 31 pts
Which example is the greatest pressure?
850 mm Hg (= 850 torr) |
1.5 atm |
All of the above pressures are equal. |
96 kPa |
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Question 41 pts
Assuming all other variables are held constant, a graph of which of the following will NOT yield a straight line?
P vs. V |
V vs. T |
P vs. T |
V vs. n |
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Question 51 pts
A sealed vessel contains 0.250 mol of oxygen gas. Which of the following will result in a decrease in the pressure of the oxygen gas?
increasing the number of moles of oxygen |
increasing the temperature of the vessel |
increasing the volume of the vessel |
adding some helium to the vessel |
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Question 61 pts
According to Charlesâs law, which change will cause the pressure of a gas to double? Pressure and amount of gas are constant.
The temperature decreases from 650 K to 325 K. |
The temperature of the sample decreases from�88 °C to 44 °C. |
The temperature of the sample increases from�22 °C to 44 °C. |
The temperature of the sample increases from�250 K to 500 K. |
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Question 71 pts
Which set of units for P, V, and T can be used for combined gas law calculations?
torr, L, and Kelvins |
tm, g/L, and Kelvins |
atm, mL, and degrees Celsius |
inches of mercury, g/mL, and degrees Celsius |
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Question 81 pts
The vapor pressure of a gas is
the atmospheric pressure at which the boiling point is determined. |
the pressure at a Kelvin temperature exactly two times the boiling point. |
impossible to determine experimentally without knowing the temperature and volume. |
the pressure above a gas sample when evaporation and condensation are balanced. |
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Question 91 pts
In a chemistry experiment where CO2 is collected over water, the atmospheric pressure is 755 mm. The partial pressure of water at the temperature in the lab is 24.2 mm. What is the pressure of the CO2?
779 mm |
731 mm |
More information is needed to answer this question |
755 mm |
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Question 101 pts
Which statement is NOT true according to the kinetic molecular theory of gases?
Molecules undergo elastic collisions |
Molecules move in straight-line paths. |
Molecules of different gases have different�kinetic energies at the same temperature |
Molecules occupy a negligible volume. |
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Question 111 pts
Which statement is NOT true according to the ideal
gas law?
At constant P & T, V must increase when n increases. |
At constant V & T, P must decrease when n decreases. |
At constant V & n, P must increase when T increases. |
At constant P & n, V must decrease when T increases |
I need help writing a decent conclusion. Every time I submit a lab report the professor slams my conclusion saying it needs work. She wants us to state what the results mean and if they are as expected and explain the possible reasons for variation in your results. The lab is below with data/results. Please, please help.
The Ideal Gas Equation: The Determination of Gas Constant, R
Introduction:
The purpose of this experiment is to determine the gas constant R and the percentage of KClO3 in the KClO3 â KCl â MnO2 mixture using the moles of O2, the original weight of the mixture, and the stoichiometry of the reaction. Consider a plot PV vs. nT for a gas sample where P is the pressure of the gas, V is the volume occupied by the gas, n is the number of moles of gas, and T is the temperature of the gas in Kelvin. If the temperatures and pressures fall in normal ranges, the plot will yield a straight line. Thus, PV = nRT where R is the constant of proportionality between the PV product and the nT product. The object of this experiment is to determine P, V, n, and T for a gas sample and determine the gas constant R, using the equation PV = nRT. The gas sample used will be a sample of oxygen gas generated by the MnO2 catalyzed decomposition of KClO3. Following is the equation of the reaction:
For decomposition of the KClO3 in a KClO3 â KCl â MnO2 mixture, the mass of O2can be determined by taking the difference between the mass of the original mixture and the mass of the residue after the decomposition. This mass is then converted to moles of O2 using the molecular weight of oxygen. The volume of the sample will be determined by water displacement in such a way that the pressure of the sample can be determined from the barometric pressure and the vapor pressure of water. The temperature of the sample will be directly measured.
Procedure:
Assemble the equipment for the apparatus shown in figure 1. With the Florence flask filled to the neck with water, the beaker one-third filled with water, and the pinch clamp open, blow into the tube which connects to the test to create a siphon between the flask and the beaker. Reverse the siphon a few times by raising and lowering the beaker. This will fill the tube connecting the flask and the beaker with water and will also remove air bubbles from the system. Adjust the siphon such that the flask is filled to the neck with water, and close the pinch clamp.
Weigh the eight inch test tube. Add approx. 1.5 grams of the KClO3 â KCl â MnO2mixture to the test tube and weigh the test tube containing the mixture. Record each weight to three decimal places. (Also, be sure and record the sample number for the KClO3 â KCl â MnO2.)
Clamp the test tube to the ring stand, and insert the stopper as shown in figure 1. With the pinch clamp open, raise the level of the beaker such that the water level in the beaker is several inches above the water level in the flask. If a significant amount of water runs into the flask, there is an air leak in the system. If you have an air leak, it must be closed before proceeding. Equalize the pressure in the flask with atmospheric pressure by bringing the water level in the beaker to the same height as the water level in the flask. After closing the pinch clamp, empty and dry the beaker. Open the pinch clamp. A small amount of water will run into the beaker: this will not affect your results since later in this experiment, you will again equalize the pressure in the flask with atmospheric pressure. Ask your instructor to check your apparatus before proceeding.
Heat the mixture with a blue flame until the mixture first begins to melt and then solidifies again; and then heat for an additional 2 mins. (Donât heat more than 7 mins.) Allow the system to cool for 15 mins. Equalize the pressure with atmospheric pressure, as before; then close the pinch clamp and open the system. Quickly measure the temperature of the gas in the flask; also measure the volume of water in the beaker. Record the barometric pressure reading from professor. Weigh the test tube with the residue and record the mass to three decimal places.
Data/Results:
Trial 1 | |
Weight of test tube | 41.912 g |
Weight of test tube + mixture | 43.343 g |
Weight of mixture | 1.431 g |
Weight of test tube + residue | 43.211 g |
Weight of oxygen | 0.132 g |
Moles of oxygen | 0.00413 mol |
Temperature of water (under oxygen) | 21.0 0C |
Temperature of oxygen | 20.5 0C |
Barometric pressure | 761.5 torr |
Vapor pressure of water | 18.7 torr |
Pressure of oxygen | 742.8 torr |
Volume of water displaced | 0.101 L |
Gas constant, R | 61.9 |
Mass of KClO3 in mixture (use balanced equation) | 0.338 g |
% of KCLO3 in mixture | 23.6 % |