High-Form Porcelain Crucibles & Lidded Covers
30 mL glazed porcelain crucibles rated to 1150 °C with closely fitting recessed covers to contain magnesium oxide aerosol during vigorous thermal oxidation.
Chemistry / Empirical Formula of MgO
FREE TO EXPLORELABORATORY 07 · NATURAL SCIENCES
Determination of the Empirical Formula of Magnesium Oxide: Crucible Thermal Oxidation
Determine the empirical formula and stoichiometric mole ratio of magnesium oxide (MgO) via quantitative thermal oxidation of high-purity magnesium ribbon in a porcelain crucible, hydrolyzing intermediate magnesium nitride with steam, calcining to constant mass, and extracting the O:Mg stoichiometric ratio using ordinary least-squares linear regression. Explore interactive analytical gravimetry, Class A volumetric glassware and density determination.
MEASURE · CALIBRATE · ANALYSE
Your virtual chemistry laboratory.
MASS OF BOUND OXYGEN INCORPORATED M_OXYGEN—
MEASUREMENT STATUS
Ready to dispense 0.5 g 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.
Physical chemistry assumptions and metrological limits
The gravimetric determination of the empirical formula of magnesium oxide is subject to distinct physical and chemical constraints: (1) Incomplete Oxidation of Internal Cores: If magnesium ribbon is rolled too tightly, outer crusts of refractory MgO (melting point 2852 °C) can insulate inner metal cores from atmospheric oxygen. (2) Aerosol Fume Losses: Even with careful lid manipulation, trace amounts of sub-micron MgO aerosol smoke escape as convection currents pulse past the lid margin. (3) Crucible Glaze Attack: At prolonged temperatures above 850 °C, basic MgO can react with acidic silicates in porcelain glaze to form magnesium silicates (MgSiO₃), slightly altering the crucible tare. (4) Atmospheric Re-Hydration and Carbonation: Highly porous, active MgO powder is strongly hygroscopic and basic; exposure to ambient air rapidly chemisorbs moisture and carbon dioxide to form Mg(OH)₂ and MgCO₃, inflating the final mass if balance transfers are delayed. The magnesium oxide empirical formula model embodies the stoichiometric relation m_oxygen = [M(O) / M(Mg)] · m_Mg. Fundamental atomic parameters: M(Mg) = 24.305 g/mol, M(O) = 15.9994 g/mol, M(MgO) = 40.3044 g/mol. Theoretical mass ratio: M(O)/M(Mg) = 0.658276 g O / g Mg. Multiplying the empirical regression slope m_slope by [M(Mg)/M(O) = 1.51912] extracts the elemental molar ratio n(O)/n(Mg) = 1.0000 mol O / mol Mg. Multi-point linear regression provides substantial advantages over single-trial calculations: constant crucible tare drift or persistent glaze moisture adsorption is absorbed directly into the intercept m₀ = 0.0000 g, guaranteeing that the regression slope represents the true, unbiased marginal stoichiometric stoichiometry of lattice oxygen incorporation.
Analytical chemistry apparatus & tools.
Meker High-Temperature Gas Burner & Clay Triangle
High-output nickel-grid Meker burner supported on an iron ring clamp and nichrome-stem clay pipe triangle to reach red-hot calcination temperatures (800–900 °C).
Crucible Tongs with Fire-Polished Nickel Tips
Curved 9-inch nickel-plated crucible tongs for safe lid adjustment and transfer of red-hot crucibles without introducing grease or mechanical chipping.
Fine Emery Cloth & Micro-Shears
600-grit silicon carbide emery paper to strip dull gray surface oxide and carbonate passivation down to shiny metallic magnesium, plus shears to section ribbon into 1 cm pieces.
Pasteur Pipettes & Boiling Deionized Water
Borosilicate glass dropping pipettes for controlled delivery of 10–12 drops of hot deionized water to hydrolyze intermediate magnesium nitride into hydroxide and ammonia.
Four-Decimal Analytical Balance & Desiccator
0.1 mg electromagnetic force restoration balance paired with a glass desiccator containing cobalt-indicator activated anhydrous calcium sulfate (Drierite).
FOLLOW THE METHOD
A reason behind every step.
Determine the empirical formula and stoichiometric mole ratio of magnesium oxide (MgO) via quantitative thermal oxidation of high-purity magnesium ribbon in a porcelain crucible, hydrolyzing intermediate magnesium nitride with steam, calcining to constant mass, and extracting the O:Mg stoichiometric ratio using ordinary least-squares linear regression. Suggested independent volumetric settings: 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 g.
01
Crucible Firing to Constant Mass
Heat a clean porcelain crucible and lid in the hottest oxidizing flame of a Meker burner for 10 minutes until the crucible base glows dull cherry red. Transfer using tongs to a desiccator, cool for 15 minutes, and weigh on an analytical balance to ±0.0001 g. Repeat firing until successive masses agree within ±0.0003 g.
02
Magnesium Preparation and Initial Weighing
Cut high-purity magnesium ribbon into 1.0–1.5 cm segments. Polish each piece vigorously with 600-grit emery cloth to expose bright silvery metal. Coil the segments loosely into the crucible bottom, replace the lid, and record the combined mass to determine the initial magnesium mass m_Mg to four decimal places.
03
Controlled Thermal Oxidation
Place the covered crucible on the clay triangle. Heat gently for 3 minutes, then tilt the lid slightly with tongs to create a 1 mm gap admitting air. If white smoke begins escaping, immediately slide the lid shut to trap airborne MgO aerosol. Continue heating strongly until the metal ceases to flare and transforms into a uniform gray-white ash.
04
Steam Digestion of Magnesium Nitride
Allow the crucible to cool to room temperature on a ceramic tile. Add 10–12 drops of boiling deionized water directly onto the ash with a Pasteur pipette (noting the faint pungent odor of escaping ammonia gas, confirming Mg₃N₂ + 6H₂O -> 3Mg(OH)₂ + 2NH₃↑).
05
Gentle Dehydration and Final Calcination
Heat the crucible with a low flame and lid ajar to evaporate water smoothly without boiling or spattering. Gradually increase flame intensity to maximum and calcine at 850 °C for 10 minutes to dehydrate Mg(OH)₂ completely into crystalline MgO.
06
Desiccation, Gravimetric Weighing and Regression
Cool the covered crucible inside a sealed desiccator for 15 minutes. Record the final mass of crucible, lid, and MgO product. Subtract initial magnesium mass to obtain bound oxygen mass m_oxygen. Plot m_oxygen against m_Mg across all six trials to extract the stoichiometric ratio n(O)/n(Mg).
YOUR NOTEBOOK · 0 OBSERVATIONS
Turn measurements into quantitative chemical insight.
Points are your recorded gravimetric observations. The regression line validates the linear mass-volume proportionality and extracts density.
ORDINARY LEAST-SQUARES FIT · m = ρ·V + m₀
m_oxygen = (M_O / M_Mg) · m_Mg + m₀ ==> m_O = 0.6583 · m_Mg
| # | Initial magnesium ribbon mass m_Mg (g) (g) | Mass of bound oxygen incorporated m_oxygen (g) | Initial magnesium mass m_Mg (g) | Bound oxygen mass m_oxygen (g) | Remove |
|---|
No readings yet. Dispense and weigh a volumetric aliquot to record it.
Calculate it yourself.
CHECK YOUR UNDERSTANDING