Question

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 – KCl – 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 – KCl – 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 – KCl – 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 – KCl – 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. (Don’t 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 %