GRADE 10TH LAB PRACTICE 1
EXPERIMENTAL DETERMINATION OF THE IDEAL GAS CONSTANT “R”
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.

V Conversion of mL to L
GRADE 10TH LAB PRACTICE 1
EXPERIMENTAL DETERMINATION OF THE IDEAL GAS CONSTANT “R”
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
%