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The Ideal Gas Constant

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Anita Yen

on 28 April 2014

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Transcript of The Ideal Gas Constant

Introduction
Ideal Gas Law Lab
The purpose of the lab was to test the ideal gas constant. We are given the formula PV = nRT, R being the ideal gas constant. The lab is used to determine the value of R.
Gas particles are unrestricted and move freely, often colliding with each other.
The Ideal Gas Constant
Equipment
In this experiment, safety precautions needed include goggles and latex gloves. Other equipment include a metric ruler, a 1.0cm strip of magnesium, 25cm thin-gauge copper wire, a graduated cylinder, 10-mL and 400 mL beaker, tap water, 3.0 M of HCL, thermometer, and a table of vapor pressures of water.
Data & Observations
Length of Mg ribbon
: 1.4 Cm
mass of 100.0 cm Mg ribbon
: 0.825 g
temperature of the reaction system
: 22 C
atmospheric pressure
: 1008 kpa
water vapor pressure at system temperature
: 2.64 kpa
volume of gas produced
: 6 mL
Data Anaylsis (Calculations)
Use R=PV/nT
Conclusions
The hydrogen gas generated in the test tube was a result of magnesium reacting with the HCl. Using the data collected from the experiment, we can calculate the gas constant. In this lab, we can assume and confirm from the kinetic molecular theory that gases consist of large numbers of tiny particles that are far apart relative to their size, collisions between gas particles and between particles and container walls have elastic collisions, gas particles are in continuous rapid, random motion, and there are no forces of attraction between gas particles. However, our experiment was not at STP, therefore this may have caused some calculation errors.
Percent Error
% Error= (the result-accepted value)/(accepted value)
Hypothesis
If all the magnesium reacts with the HCL, and all our calculations and observations are accurate, then we should be able to find the gas constant (R) to be 8.314 L*kpa/mol*k. Since R is a constant, it should always be the same value, only if the kinetic molecular theory conditions are met. 1) They must have perfect elasticity. 2) The total energy must remain constant.
Applications to the "real world"
Thanks For Watching!
Procedure
First, you must collect data needed. Second, you wrap the copper wire around the magnesium strip, securing it. Leave a handle of copper wire approximately 6 cm long. Third, fill the test tube with 10 mL of HCl, and completely fill the the rest of the test tube with water. Fourth, insert the magnesium and copper wire into the test tube (of water and HCl) with the 6cm handle of copper wire hanging from the test tube. Fifth, insert the test tube into the graduated cylinder (filled with water), making sure the magnesium strip does not fall out. Sixth, watch and observe the hydrogen gas forming in the test tube.
P=98.16 Kpa V= 0.01 L n=0.000475 mol
T= 295 K
Ideal Gas Law
R=(98.16kpa)(0.01L)/(0.000475mol)(295 K)
R= 7.005 L*kpa/mol*K
When the acid descended to the bottom and touched magnesium, bubbles began to form and travel up the test tube. The copper wire remained unreactive.
Hot Air Balloon
Soda Can
Spray Cans
% Error= (7.005 L*kpa/mol*K)-(8.314 L*kpa/mol*K)
/
8.314 (L*kpa/mol*K)
% Error= 0.157*100%= 15.7%
Class Question
Co2
O2
He
N2
CH4
Represented above are 5 identical balloons, each filled to the same volume at 25C and 1.0 atm with the pure pressure indicated
1. Which balloon contains the greatest mass of gas? Explain.
2. Compare the average kinetic energies of the gas molecules in the balloon. Explain.
3. Which balloon contains the gas that would be expected to deviate most from the behavior of an ideal gas? Explain.
4. 12 hours after being filled, all the balloons have decreased in size. Predict which balloon will be the smallest. Explain your reasoning.
Answers
1. Co2 because all contain some number of molecules (moles), and Co2 molecules are the heaviest.
2. All are equal, the same temperature means the same average kinetic energy.
3. Co2, it has the strongest intermolecular (London) forces and inelastic collisions
4. He, it has the smallest, greater molecular speed, greatest movement through the balloon wall, and most rapid effusion
Conclusions (Continued)
Error & Suggested
Alterations
Contributions to percent error include: not allowing the Mg strip to full react, allowing some of the hydrogen gas to escape, not keeping the temperature constant, and also the hydrogen gas was not kept at STP. To avoid experimental and calculation errors, we could have been more careful during the submerging of the magnesium strip into the graduated cylinder, regulated the temperature of the water more thoroughly, and waited/checked to see if the Mg strip completely reacted.
Our conclusion matched our hypothesis, however since all conditions of the KMT (stated above) were not met our experimental value for the gas constant did not equal 8.314 L*atm/K*mol.R which is known as the universal gas constant can be applied to the ideal gas law and other fundamental chemical formulas as well. The gas constant is the constant of proportionality that happens to relate the energy scale in physics to the temperature scale, when a mole of particles at the stated temperature is being considered.
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