Jessica Brown
December 16, 2008
Chemistry Lab Write-up
Decomposition of KClO3
Purpose:
To determine the value of the gas constant, R, by measuring the decomposition of potassium
chlorate, KClO3, using a liquid method.
Procedure:
The procedure used is in the lab manual under Experiment #2, Decomposition of KClO3. Nothing
was altered. All the steps found in this lab is the procedure we used.
Data:
Table #2: Moles of O2 Evolved
Mass of Test Tube +
reactants (g)
Mass of Test Tube +
products (g)
Mass of O2 evolved (g)
Moles of O2 evolved
(mole)
Trial 1
18.748g
Trial 2
18.692g
Trial 3
18.686g
18.775g
18.642g
18.637g
0.027g
0.0017mole
0.05g
0.0031mole
0.049g
0.00306mole
Table #3: Volume of Water Displaced
Mass of Dry Beaker (g)
Mass of Beaker + Water
(g)
Mass of water displaced
(g)
Temperature of water
(C)
Density of water (g/mL)
Volume of water
displaced, V2 – V1
Trial 1
24.976g
170.252g
Trial 2
25.196g
83.009g
Trial 3
25.440g
78.968g
145.276g
57.813g
53.528g
22 oC
23 oC
21.5 oC
0.9977g/mL
145.6007 g/mL
0.9975g/mL
57.958 g/mL
0.9978g/mL
53.646 g/mL
Table #4: Determination of Gas Constant
Trial 1
Trial 2
Trial 3
Average, X
Standard Deviation
95% Conf. Int. X +/- lambda
Sample Calculations:
R from eq. 3
0.287 Latm/molK
0.062 Latm/molK
0.059 Latm/molK
0.0499 Latm/molK
0.086 Latm/molK
0.07562 +/- 0.0051
R from eq. 4
0.125 Latm/molK
0.043 Latm/molK
0.047 Latm/molK
0.072 Latm/molK
0.036 Latm/molK
0.0757 +/- 0.0037
Mass of Water displaced and Mass of O2 Evolved
(Mass of beaker/test tube + reactants) – (Mass of test tube/beaker + products)
18.692g-18.642g = 0.05g
Moles of O2 Evolved
Mass of Oxygen Evolved/Molar Mass of Oxygen
0.05g/32g = 0.0031g
Volume of Water Displaced:
V=mass of water displaced/density of water
V=57.813g/0.998L
V=57.92mL = 0.0579L
R value using Ideal Gas Laws:
NO2=(V2-V1)P/RT
0.0031moles = (0.0579L)(0.990atm)/R(296.15K)
R=0.062L*atm/mol*K
R Value using van der Waals forces:
(
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)
)
(
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( ) )(
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) )(
(
))
R= 0.0426 L*atm/mol*K
Questions:
1. Yes, all of them except for one of the R values agree with the accepted value within the
confidence limits of the results. Trials two and three were within the value due to
experimental error trial one was not within the confidence limits.
2. Yes, only two of them were within the confidence limits of the van der Waals equation.
Trials two and three were within the value due to experimental error trial one was not
within the confidence limits.
3. The amount of oxygen in the test tube determines pressure of the oxygen changing the
R value.
4. 0.991 atm
5. 0.0596 g KClO3
6. C6H6
Conclusions:
Most gases obey the ideal gas equation and the ideal gas law. The ideal gas law states, that the
product of the pressure and the volume of one gram molecule of an ideal gas is equal to the product of
the absolute temperature of the gas and the universal gas constant. The equation for this is PV=nRT. P
is the pressure in atmospheric pressure, V is volume in L, n is moles of the gas, R is the gas constant
0.08206 Latm/molK, and T is temperature in Kelvin’s. Real-gas molecules are finite in size and exhibit
mutual attractive forces, the van der Waals equation can accommodate for all of that. The equation is
(P+ (n2a/V2))(V-nb) = nRT. In this equation P, V, and n are the same as in the ideal gas equation, while a
and b are constants characteristics of a given.
In this experiment, MnO2 will be used as a catalyst to speed up the decomposition reaction. A
catalyst is a substance that causes or accelerates a chemical reaction without itself being affected. The
reaction in this experiment was 2KClO3(s)  2KCl(s) + 3O2(g). The error throughout this lab was human
error, placing too much water into the beaker, not letting the reaction complete itself, and not
measuring the water and components correctly. Improvements for this lab would be to use more
accurate equipment, and to put the equipment under the hood to make sure everyone is safe because
the pressure could build up inside the test tube causing the rubber stopper to shoot off the end, or the
glass to break.