GRADE 10TH LAB PRACTICE 1
EXPERIMENTAL DETERMINATION OF THE IDEAL GAS CONSTANT “R”
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A. OBJECTIVE
To determine the value of the universal gas constant, R.
B. MATERIALS
Equipment: Balance, tweezers, 25x200 mm boiling test tube, Syringe, barometer, 2x100mL glass beakers,
10mL pipet, pipet pump, glass tubing bent, 2 ring stands, 2 utility clamps, rubber stopper, Tygon tubing
(hoss), thermometer. REACTANTS: 1.0M HCl, 0.1M HCl, Magnesium ribbon, distilled and tap water.
C. PROCEDURE
1. Set up your apparatus for hydrogen gas collection
2. Use sandpaper to remove the magnesium coating, rinse it with distilled water and dry with a paper towel.
3. The magnesium should weigh approximately 0.016 – 0.018 g
4. Pour 4 mL of 1M HCl in a test tube using 10 mL pipet
5. Transfer the magnesium weighed into the test tube with the HCl solution that was tilted without touching
the HCl solution
6. While the rubber stopper was inserted carefully into the tube, the tube was rotated to allow the
magnesium to slide down into the solution. Flip it into a water container to allow the water and hydrogen
gas exchange
7. Look for initial and final volume, after the chemical reaction is over. Calculate the difference in volume,
which belongs to the hydrogen gas volume produced
D. CONVERSION FACTORS:
1atm = 760 mm Hg
0°C = 273 K
1L = 1000 mL
E. CALCULATIONS:
Chm rx unbalanced:
Mg (s) + HCl (aq)  MgCl2 (aq) + H2 (g)
Chm rx already balanced:
Mg (s) + 2 HCl (aq)  MgCl2 (aq) + H2 (g)
Ratio Mg:H2
1:1
Means that 1 mole of metallic magnesium ribbon will yield 1 mole of hydrogen gas.


Starting number of moles metallic Mg:
Mol Mg = Mass of Mg x 1 mol / 24.305 g (from the periodic table)
Your sample grams
g x 1 mol / 24.305 g =
 Producing/yielding number of moles of H2 gas:
mol
Scientific Notation
mol
mol
Note: Since Mg and H2 have the same ratio 1:1 in the already balanced chemical equation, both have the
same number of moles. 1 mole of metallic magnesium ribbon will yield 1 mole of hydrogen gas.
GRADE 10TH LAB PRACTICE 1
EXPERIMENTAL DETERMINATION OF THE IDEAL GAS CONSTANT “R”
https://www.studocu.com/en-us/document/laguardia-community-college/topics-in-chemistry/lab-report-10-determination-of-the-gas-law-constant/3490995

V Conversion of mL to L
Gas volume produced in mL conversion = (

T

P Corrected Barometric Pressure
mL) (1L / 1000mL) =
L
°C T = 273 K + ˚C
temperature in Kelvin unit when room temperature is
T=
K
Look for temperature and vapor pressure of water from the chart, in mm Hg or atm:
Co. Pres. = Barometric pressure - Vapor pressure
Co. Pres. = 761.102 mm Hg Co. Pres. =
mm Hg
mm Hg
Co. Pres. =
atm
Corrected pressure calculated in atm:
Co. Pres. = Barometric pressure – Water Vapor pressure

Co. Pres. =
atm
Co. Pres. =
atm
-
atm
R Determine the gas constant (R) EXAMPLE:
PV=nRT
The actual value of gas constant is 0.08205 atm L/ mol K
Rearrangement:
R = PV
nT
=
0.982 atm
x 0.014 L = 0.0781 atm L
0.000597 mol x 295 K
mol K
% ERROR
The accepted value is the one known from bibliography as the constant value, the one with the right units.
Percentage error = [ the accepted value – the experimental value ] x 100 %
the accepted value
% error = [ 0.08205 atm L/mol K atm L/ mol K ] x 100%
0.08205 atm L/ mol K
Resulting % error =
F. MEANINGFUL CONCLUSIONS
%
GRADE 10TH LAB PRACTICE 1
EXPERIMENTAL DETERMINATION OF THE IDEAL GAS CONSTANT “R”
https://www.studocu.com/en-us/document/laguardia-community-college/topics-in-chemistry/lab-report-10-determination-of-the-gas-law-constant/3490995
DISUSSION
Results Obtained
Gases are the third normal state of the matter. Some element and molecular compounds are gases at R,
T, and normal pressure. Commonly, gases are characterized by four physical properties, such as volume
which is the amount of space that gas occupies in Liters; moles of the gas; temperature which measure the
average kinetic energy of gas molecule in Kelvin; and the pressure which is the force that exerted by gas
molecules as the molecules collide with wall in an enclosed container in atmosphere. The scientists who
study gases discover V α 1 /P as Boyle's Law states that the volume of a gas sample is proportional to the
inverse of its pressure at constant temperature, V α T as Charles' Law showed that the volume of a gas
sample is proportional to its absolute temperature at constant pressure, and V α n as Avogadro's Law states
in effect that the volume of a gas sample is proportional to the number of moles of gas. The combination of
three proportional laws give the equation such V α nT/P. In this experiment, the reaction of magnesium
metal with hydrochloric acid to produced magnesium chloride and hydrogen gas was to find the gas law
constant.
Mg(s) + 2 HCl(aq)  MgCl2(aq) + H2(g)
The room temperature and the barometer pressure were constant. After the volume of hydrogen gas was
founded by collecting the gas in the syringe and the number moles was also found by using the molar mass.
The gas constant (R) could be determined by using the ideal gas law from the three proportional equations
which was given R = P.V/ n.T. As a result, the gas law constant was obtained which was 0.07814
L.atm/K.mol for the first trial, 0.07993 L.atm/K.mol for the second trial, 0.08099 L.atm/K.mol for the third
trial and 0.07880 L.atm/K.mol for the fourth trial. Then, the average of the both trials could be determined
which was 0.07947 L.atm/ K.mol. As the average of the trials was compared with the actual value of gas
constant which was0.08205 L.atm/K.mol, thoroughly, the percentage error of this experiment little bit high
because of several factors which was 3.14 %. Therefore, the method of this experiment with using the
syringe to acquire the volume of the gas was not 100% accurate. However, this method was still useful to
know how to determine the result of the gas law constant, where R, T, and normal pressure were the main
figure of the R.
Errors
There were several factors that affected this experiment to the accuracy of the calculations. The
concentration of the solution might be contaminated or it might not be 100 % perfect due to many users.
Also, the instrumental measurements that were used were not always in perfect condition, such as the
balance which might not read correctly the weight of magnesium metal because it was the limited reagent
for the experiment, and the barometer which might not read correctly the atmospheric pressure. The
rubbers might already lose the elasticity. It was part human error when it came to read the manual scale of
the instruments such as the glass beakers, the syringe or the pipet.
Precautions
To reduce the error of measuring, when transferring the solution from the pipet to the boiling test tube, wait
20-30 more second to drain the solution so the volume of the solution was more accurate. After rinsing the
magnesium metal with distilled water, it should be dried with a paper towel. The glass around the balance
should be closed when measuring the weight of the magnesium metal to reduce the air flow. Also, the
balance should read zero with the wax paper before the metal was placed on the top of it. The pipet should
be rinsed with the standard solution of 1M HCl to avoid contamination. The HCl solution was corrosive and
GRADE 10TH LAB PRACTICE 1
EXPERIMENTAL DETERMINATION OF THE IDEAL GAS CONSTANT “R”
https://www.studocu.com/en-us/document/laguardia-community-college/topics-in-chemistry/lab-report-10-determination-of-the-gas-law-constant/3490995
toxic and it should be avoided to contact with the skin. When the metal was dipped into the HCl solution by
using the tweezers, the tweezers should not contact with the solution because the tweezers would
contaminate the hydrochloric acid solution and the solution could not perfectly remove the magnesium’s
coating. When the syringe with the tygon tubing was set by using the utility clamp on a ring stand, its position
should be connected straight horizontally. The boiling test tube should remain titled so it prevented the
magnesium from sliding into the HCl solution when it was put inside the wall of the tube or it meant that if
the magnesium were to slide into the HCl in the boiling tube before the system was sealed off, because the
magnesium metal would react with the HCl or the reaction would proceed and some the hydrogen gas
product would be lost and the result would not accurate. The syringe could be recorded for at least 5 minutes
when the reaction allowed the system to equilibrate because 0.0145 grams of magnesium metal should
completely react with the volume solution of HCl.
G. CONCLUSION
As a result of this experiment, the reaction of magnesium metal with hydrochloric acid to produce hydrogen
gas and magnesium chloride gave the value of the constant gas which was 0.07947 L.atm/ K.mol.
Therefore, since the percentage error was too small (3.14 %), it was proved that this evaluation method or
experiment gave the satisfactory results for the gas law constant.
H. REFERENCE
Brown, Theodore L.; LeMay, H. Eugene; Bursten, Bruce E.; Chemistry: The Central
Science, 11th Edition, Prentice-Hall, 2008.
Miller, D. (2013) General Chemistry I Laboratory Manual.Kendall Hunt.
Miller, Dionne A. (Second Edition.); SCC201 Fundamentals of Chemistry Laboratory
Manual; Cengage Learning, 2009, pp 25 – 32.