Quantitatively determine the molar volume of hydrogen gas at Standard Temperature and Pressure (STP: 273.15 K, 101.325 kPa) via the single displacement reaction between metallic magnesium and hydrochloric acid, applying Dalton's law of partial pressures for aqueous vapor pressure and liquid hydrostatic head corrections, and extracting the empirical molar volume via ordinary least-squares regression. Explore interactive analytical gravimetry, Class A volumetric glassware and density determination.
Ready to dispense 25.0 mg of liquid.
Adjust magnesium mass V, then weigh the dispensed aliquot.
Mass observations are determined by the high-precision thermodynamic equation of state for pure liquid water. Readings reflect thermal equilibrium and analytical balance force restoration.
The determination of ideal gas molar volume via eudiometric hydrogen displacement is subject to specific physical constraints: (1) Real Gas Non-Ideality: Hydrogen molecules exhibit finite molecular excluded volume (van der Waals b = 0.0266 L/mol), causing real hydrogen molar volume at STP to be 22.428 L/mol rather than the ideal 22.414 L/mol (a +0.062% offset). (2) Aqueous Gas Solubility: Hydrogen has a small but finite solubility in water (~1.9 mL/L at 20 °C), resulting in the dissolution of approximately 0.05 mL of H₂ in the aqueous column. (3) Meniscus Parallax and Glass Drainage: Capillary depression and water drainage films along the eudiometer wall contribute ±0.03 mL of random reading uncertainty. (4) Atmospheric Barometric Drift: Minor barometric pressure changes during an extended multi-trial session can introduce small baseline drifts unless monitored concurrently. The eudiometric gas model incorporates four coupled thermodynamic and hydrodynamic corrections: (1) Stoichiometric mole equivalence n(H₂) = m_Mg / 24.305 g/mol; (2) Dalton's law of partial pressures subtracting the temperature-dependent equilibrium saturation vapor pressure of liquid water P_H2O*(T) formulated via the Antoine equation log₁₀(P) = A - B / (T + C); (3) Hydrostatic head elimination by matching the internal and external water menisci inside the tall leveling jar (or applying the mercury-equivalent hydrostatic correction ΔP_head = Δh_water / 13.595 mmHg); and (4) Combined gas law reduction to Standard Temperature and Pressure (T_0 = 273.15 K, P_0 = 760.0 mmHg). The regression slope m_slope = V_m,STP / M_Mg relates directly to the molar volume of hydrogen gas, achieving sub-0.05% agreement with the theoretical value of 22.414 L/mol.
50.00 mL borosilicate glass eudiometer tube with permanently fused ceramic white graduations every 0.10 mL (Class A tolerance ±0.05 mL), closed and rounded at the top to trap all evolved hydrogen gas without bubble loss.
1000 mL heavy-walled borosilicate graduated leveling jar filled with deionized water, allowing the eudiometer to be submerged to match internal and external liquid menisci, completely neutralizing the hydrostatic column pressure.
High-purity spiraled copper wire (gauge 20) cage that mechanically secures the folded magnesium ribbon at the bottom orifice of the eudiometer, preventing buoyant magnesium fragments from floating into the calibrated tube before dissolution.
Mercury Fortin barometer (vernier resolution ±0.1 mmHg) equipped with brass scale temperature correction, paired with a NIST-traceable digital immersion thermistor (resolution ±0.05 °C) to monitor ambient pressure and bath temperature.
Size 00 one-hole neoprene stopper with glass capillary insert to seal the eudiometer while allowing water displacement, and a calibrated 10 mL pipette for bottom-layering concentrated 6.0 M HCl.
Five-place electromagnetic force restoration microbalance with 0.01 mg (0.00001 g) readability and draft enclosure to determine exact masses of cleaned magnesium ribbon strips.
Quantitatively determine the molar volume of hydrogen gas at Standard Temperature and Pressure (STP: 273.15 K, 101.325 kPa) via the single displacement reaction between metallic magnesium and hydrochloric acid, applying Dalton's law of partial pressures for aqueous vapor pressure and liquid hydrostatic head corrections, and extracting the empirical molar volume via ordinary least-squares regression. Suggested independent volumetric settings: 10.0, 15.0, 20.0, 25.0, 30.0, 35.0 mg.
Thoroughly abrade high-purity magnesium ribbon strips with fine 600-grit silicon carbide emery cloth until a bright, silvery metallic luster is achieved, completely removing passivating magnesium oxide (MgO) and carbonate crusts; wipe with a lint-free tissue and weigh to ±0.01 mg on the analytical microbalance.
Fold the weighed magnesium strip into an accordion zig-zag and encase it tightly within a fine copper wire cage, leaving a 10 cm copper tail; introduce 10.0 mL of 6.0 M HCl into the bottom of the dry eudiometer tube, then slowly and carefully overlay deionized water down the tilted tube wall to fill it to the brim without mixing the dense acid layer.
Insert the copper wire tail through the one-hole neoprene stopper so the magnesium cage is positioned approximately 3 cm into the tube mouth; insert the stopper firmly, seal the hole with a gloved finger, and invert the eudiometer into a 1000 mL beaker of deionized water before clamping it vertically to a ring stand.
As the denser 6 M HCl diffuses downward under gravity through the water column, it reaches the magnesium ribbon, initiating a vigorous, effervescent displacement reaction: Mg(s) + 2HCl(aq) -> MgCl2(aq) + H2(g); hydrogen gas ascends rapidly, displacing water downward through the stopper until the metal dissolves completely; allow 15 minutes for the eudiometer to cool to ambient bath temperature.
Unclamp the eudiometer and transfer it into the tall-form 1000 mL leveling cylinder; raise or lower the tube until the liquid level inside the eudiometer aligns precisely with the water level in the external cylinder, equalizing total internal gas pressure with atmospheric pressure (P_gas = P_atm); record the gas volume to the nearest 0.05 mL, and measure bath temperature and barometric pressure.
Subtract the equilibrium saturated water vapor pressure P_H2O*(T) from barometric pressure to isolate dry hydrogen pressure P_H2; convert measured volume to Standard Temperature and Pressure (STP: 273.15 K, 760.0 mmHg) using the combined gas law; repeat across six magnesium masses (10.0 to 35.0 mg), tabulate data, and apply ordinary least-squares regression of V_STP versus m_Mg to extract the molar volume V_m,STP.
Points are your recorded gravimetric observations. The regression line validates the linear mass-volume proportionality and extracts density.
| # | Magnesium ribbon reactant mass m_Mg (mg) (mg) | Standardized dry H₂ volume at STP V_STP (mL) | Reacted magnesium mass m_Mg (mg) | Corrected hydrogen volume at STP V_STP (mL) | Remove |
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